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"Tank and anti-tank gun SNAFU Chart" Topic

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World War Two on the Land

1,085 hits since 5 Oct 2018
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Wolfhag Supporting Member of TMP05 Oct 2018 8:10 a.m. PST

I'm working on a 1:1 scale tank combat game and want to be able to recreate some of the historical screwups, SNAFU's, mistakes, etc that happened to crews in WWII. I want mostly human factor aspects but also common equipment malfunctions and breakdowns.


I know there are a number of former tank crewman out there that can help and maybe relate some of their "unique" experiences in training or combat.

I'm looking for historical or AAR type stuff, not really interested in the comical aspects. The chances of these occurrences are 5% to 10% each time a unit fires.

Any help or feedback appreciated.


Stryderg05 Oct 2018 10:50 a.m. PST

This is strictly from my vastly non-existent tanker knowledge: (yeah, you read that correctly)

Loader bangs hands / fumbles latch – takes longer to load next round.

Commander gives fire order early/late – shot has higher chance of missing.

Other than that (if you even want to use them), seems to be a well rounded and really detailed list.
Good luck with the rules!

Mobius Supporting Member of TMP05 Oct 2018 11:02 a.m. PST

A friend who was a gunner on an M60 had one. He dropped an APDS round and bent the tip. The Army actually made him pay for the round.

UshCha05 Oct 2018 11:19 a.m. PST

wolfhag, 5% to 10% occurrence per shot looks way off. Perhaps one per game would be more realistic.

deephorse05 Oct 2018 12:38 p.m. PST

This has the makings of Seekrieg 5 for tanks, and for that very reason I will give it a wide berth. The odds of many of those things happening seem way too high.

Wolfhag Supporting Member of TMP05 Oct 2018 1:04 p.m. PST

Thanks guys.

Mobius: Did he get to keep the APDS round after he paid for it?

UshCha: Realistic based on what data? I could not find any and I did a lot of searching too but I'm open to suggestions. I think there are too many random, unknown and human factors involved to make it objective.

deephorse: yes, way too high but they do happen. Just the fact they are there and can happen puts some suspense into the game even if they never occur.

You know the old saying about Friction it will happen at the worst possible time.

In the game, it happens when you are rolling the dice to shoot (it's not a random event). I use a D20 for the Basic game and 2D10 (1-100) for the Advanced(?) game. With the D20 a 20 is always a miss and SNAFU Check so a 5% chance. With the 2D10 any double is a SNAFU Check or I could just make it even doubles only (00, 22, 44, 66, 88) for a 5% chance. Right now it's a 7% chance for a Weapon/Crew SNAFU and a 3% chance for an equipment malfunction. There are a few results that apply to the target, not the shooter, to make it a little more interesting.

The basic gameplay revolves around the timing of events for each unit with a "turn" equal to 1 second. Getting a shot off can take from 4-15+ seconds with some Risk-Reward decisions for the player to vary the timing. As each turn is announced all units scheduled to shoot for that turn do so and determine their next order and timing of the next Action Turn (no orders phase). This keeps all units synchronized to the same turn and keeps everyone in the game at all times. When a turn is announced and no one is shooting the next turn is immediately called out. Kind of like "the clock is ticking".

The chart does not have a lot of "catastrophic" events like total equipment breakdowns. Most are events that will throw off the timing of the future "Action Turn" making it harder to estimate when events occur. Your crew is not always going to do exactly what you tell them when you tell them to do it, they can screw up, choke and make mistakes. That's the whole idea. Better crews perform the same action more quickly than poor crews. Timing, not die roll modifiers or random activations, dominates the game.

These small timing variations increase the Fog of War and keep the opponents guessing, I think that's important. You never really know who is going to shoot when the next turn is announced. This gets really interesting in a 1:1 shootout when the first round from each tank misses. Seconds really do count. Players try to outguess and predict their opponent's timing decision to shoot first. Split second player decisions are more important than dice rolls.

In playtesting this chart (in different variations) has been a real crowd pleaser. Why? Because it creates suspense between the shooter and the target during the most important event of the game shooting. Even with an almost 100% chance of hitting and penetrating you can have a misfire, the driver can panic, etc throwing the shot off. These are all real-life events that are documented happening in WWII.

Rolling doubles spread out the numbers and make the SNAFU Check easily identifiable. I've tried to include events that I've come across in my reading of biographies, AAR's and other sources.

Players seem to like the "colorful" description better than a bland result like a die roll modifier. It kind of humanizes the game. I keep it more for the entertainment value more than anything else but I don't want it to dominate the game either. In games with four players and 20-30 vehicles total we normally get 2-5 SNAFU events in a 3-hour game. The only people that have complained have been the ones on the receiving end of SNAFU's. I like it that way and a half dozen extra die rolls are not going to kill the game.

To quote Otto Carius, "Everything depends on prompt identification of a dangerous target, usually seconds decide".

The one-second timing element allows those seconds to decide the results and the SNAFU's keep it interesting, suspenseful and unpredictable. I like it that way too. I understand it's not going to please everyone and that's OK too.


Legion 405 Oct 2018 1:49 p.m. PST

Does look like some good work there Wolf !

22ndFoot05 Oct 2018 1:55 p.m. PST

On "00" I suspect you mean that this is not detected by the target. The shooter will know all too well.

Mobius Supporting Member of TMP05 Oct 2018 2:36 p.m. PST

Mobius: Did he get to keep the APDS round after he paid for it?
I was thinking that. He would of gotten more than the $800 USD and so dollars from a collector.

Wolfhag Supporting Member of TMP05 Oct 2018 3:20 p.m. PST

Legion: I'm meeting with a California based publisher next weekend and an independent well know developer next week. I'll have a demo/trial version as a free PDF ready in November. You are on the mailing list so standby.

The data cards will be programmed with the augmented reality phone app to bring up short instructional videos on your cell phone so you don't have to look up rules. If you like the basic turn system maybe we can make some changes for Hammers Slammers.

22nd Foot: The "00" result I took from a recounting of German tank crew member (Otto Carius?) where they had a misfire and the loader didn't wait the full 7 seconds to see if it was a hang fire. When he opened the breach the shell came out and the casing (not the warhead) exploded (it was a indeed a hang fire) killing the loader and wounding everyone else but the tank did not explode.

The reason the note of "The shooter did not detect it" is that the game uses Limited Intelligence for damage. This forces the shooter to continue firing until he sees a visual confirmation of a fire or ammo/fuel explosion. Most of the time a tank needs two penetrating shots and occasionally three to get that verification.


Mark 105 Oct 2018 6:00 p.m. PST


On "00" I suspect you mean that this is not detected by the target. The shooter will know all too well.

The reason the note of "The shooter did not detect it" is that the game uses Limited Intelligence for damage. This forces the shooter to continue firing until he sees a visual confirmation of a fire or ammo/fuel explosion. Most of the time a tank needs two penetrating shots and occasionally three to get that verification.

Not meaning to speak for 22ndF here, but, allow me to speak for 22ndF. I think this is what he was pointing out:

Borrowing your Otto Carius example (to ensure we are all on the same page), the sequence was that in Carius' tank, the gun hang-fired, the loader opened the breach, and the round blew up inside Carius' tank. Right?

Reading what you have on the chart for "00", what we can infer is that Carius didn't notice it. I think 22ndF is pointing out that Carius probably DID notice it, even if his opponent did not. Carius was the SHOOTER, his opponent was the TARGET. The SHOOTER probably did notice it, even if the TARGET did not.

(aka: Mk 1)

Buck21505 Oct 2018 6:07 p.m. PST

Add in the possibility the loader is a young, new, Bleeped text recruit who did not take the safety off the main gun during action. Happened to me. Only in gunnery training, thankfully, not battle…

Mark 105 Oct 2018 6:18 p.m. PST

Might want another issue too about using the appropriate sight selection for HE vs. AP. May apply only to some guns, but I saw this happen even with top-rated crews on Yano Range (Ft. Knox). I was watching the "Tiger Comp", a gunnery competition among the top hand-picked crews from each of the USMC's four tank battalions. The gunner in one of the four tanks did not switch sights when he switched from HEAT to Sabot. I am pretty sure the next round landed somewhere in Ohio.

(aka: Mk 1)

Thresher01 Supporting Member of TMP06 Oct 2018 1:29 a.m. PST

Looks pretty good.

For German tanks – smoke discharger hit by MG round, and goes off, blinding the panzer/jagdpanzer crew for X turns.

Substitute paint rounds for AP/HE, if playing Kelly's Heroes, and in Oddball's Sherman (yes, I know, it's not historical, but certainly could be fun, if you are an evil GM).


Turret – Power Traverse Failure
Turret – Power Traverse Speed Reduced
Turret Jammed

Driver hits big bump/dip at speed and loses control of vehicle, while moving cross-country

Driver turns too sharply in soft ground and vehicle throws a track

Driver stalls engine – no movement this turn

Tank commander hit by hatch and knocked out, due to rough ground, and moving too quickly over it

Loader slams hand in gun breech, and is incapacitated, if not crippled

Andy ONeill06 Oct 2018 8:23 a.m. PST

Do you have a separate blue on blue in your rules?
If not how about.

Mistaken identity
Shoots friendly tank… on some criteria… maybe if different platoon within 20 degrees of frontal arc or some such.
If none qualify then does not fire this round thinking the tank targeted might be friendly.

Thresher01 Supporting Member of TMP06 Oct 2018 10:33 a.m. PST

Vehicle breakdown.

emckinney06 Oct 2018 10:48 a.m. PST

Since I've playrd the game …

Don't let the on second "turns" put you off. I thought they were going to be a disaster, but they're really just a timing mechanism. They actually nearly eliminate the need for a sequence of play because you're much less likely ti have two events occur in the same "turn!"

Wolfhag Supporting Member of TMP06 Oct 2018 3:55 p.m. PST

Thanks again, guys. I'll be adding some of these. I especially like the safety accidentally being activated. Also, the loader and commander can be injured by the gun's recoil.

The chart I posted is for crew SNAFU's, mistakes and screw-ups. Regarding turret traverse jams/malfunctions and movement is on a different SNAFU Chart.

Regarding the "00" result: IIRC Carius did see what was happening as Mark 1 stated but since they were able to bail out I don't think it caused a catastrophic explosion of the ammo storage which is what visually would have been seen. I'm sure the hatches, if not locked down, would blow open and there'd be smoke but in my opinion, in the heat of battle, the shooter would put another round into the target but I'm open to new info.

When in doubt, shoot again, just like the Pershing gunner at Cologne did pumping three rounds into a Panther. I think he said the gun was pointed right at him and he had no idea what the gunner was doing or if he was still alive so he kept firing as fast as he could.

Currently, there is a 7% chance for a crew SNAFU and 3% for a Mechanical SNAFU each time a shot is taken. The "00" result is a 1% chance out of 7% so the chances are extremely rare as was the event (0.0007). The entertaining aspect is the players seeing the chance that it can occur even though it may never occur. Players think it's cool so I keep it.

mckinney: Yes, experienced players that first see the game have the same opinion and feel the level of detail (one second turns, historic turret traverse and rate of fire without abstractions) is ridiculous and unplayable. They are slow to understand that a turn is simply a timing measurement and not a traditional turn where all activity, movement, activations, etc is performed. The one second turns allow more historic performance of weapons systems as they are normally measured in seconds or minutes so minimal abstraction is needed without impacting play.

The game "flows" from turn to turn with units activating when their Action Turn is announced rather than breaking a turn into different abstracted phases and segments activating units in an attempt to fit all activities into a 15-90 second turn. There are no special rules for opportunity fire because movement rate and rate of fire are in synch.

Because the game system can deliver these "split second" results, SNAFU's that increase the Action Turn just a few seconds can have a huge impact and will happen at the worst possible time. You do not have total control over your crew's effectiveness. It also adds some "color commentary" to the game.

Surprisingly, people in the 15-25 age bracket with minimal war game experience have caught on the quickest (without reading the rules) and seem to have a better ability to understand the "flow" of the game and can "visualize" better what will happen in 10-30 turns.

Most of the old timers are waiting to be told what they can and cannot do based on a traditional game sequence that is not used but eventually they catch on. Since all units are always active and can respond to a threat on the turn it occurs. That means you need to pay attention to everything happening as you are not waiting for your "turn" to do something.


advocate07 Oct 2018 7:52 a.m. PST

5% chance of a 1% chance – 1 for every 2,000 rounds fired – of one's own shell destroying the tank. If a 10% chance, 1 for every 1,000 rounds. It's too high.

Going in to Juno beach, SP artillery fired 100+ rounds each in imperfect conditions (so arguably higher chance of mishap). 5-10 mishaps per gun, and one in 10-20 blow themselves up.

Really you can replace many with – Mishap, 2D6 turns delay.

Personal logo 4th Cuirassier Supporting Member of TMP08 Oct 2018 2:50 a.m. PST

I like the 1-second "turns". A wargame is after all a computer game on a very big monitor with a very poor frame rate.

Wolfhag Supporting Member of TMP08 Oct 2018 4:37 p.m. PST

I've been looking for info on misfires and all I could find is 1 in 300,000 for the M1 Abrams. My SNAFU chart is pretty subjective since I can't find any hard data collection to justify the chances so I have to go with an estimate, what's playable and what's entertaining. The entries are things that historically did happen, that's important. Labeling things a "Mishap" would work (especially for larger games) but not give the crew level detail that players seem to like.

4th Cuirassier:
That's EXACTLY how I explain the game to the younger crowd that has played tank video games. Frame rates = turns, there is not an action like firing in each frame, the same as the game.

They understand the timing factors that determine spotting/reaction, turret rotation and aim time. In the video games the aiming circle gets smaller (showing smaller shot dispersion) the longer you aim. The game works the same way with a Risk-Reward decision by the player to shoot sooner with an accuracy penalty.

In my game, firing with less than maximum aim time (includes range estimation for ranging shots) is an accuracy penalty but it's a good tactic at close ranges where accuracy is very good. Variable aim time makes it harder to predict the turn of firing and helps create a Fog of War.

Since the video game automatically does reloads, most players initially forget to determine their timing for the next shot IMMEDIATELY after firing (reload + aim time) as there is no orders phase. You need to think and act like a tank crew and not wait for your "turn" to do something. However, they do know about different tactics and can use them the same way in the game.

Since they understand the basics there is no need for traditional game sequences or activation rules. All of the timing information is on a data card customized for the specific vehicle model. Once they know how to read and navigate the vehicle data card and see a few samples turns, they are good to go no need to read the rules for most of the game.

However, the video game does not have crew or maintenance SNAFU's that will happen at the worst time (when engaged and firing).

One last thing. If a player forgets to fire when his turn is announced he can fire in a later turn if still alive and he still has a target (it may have moved out of his LOS). I call it a "player generated delay". Just like in a real battlefield, you need to pay attention. You snooze, you lose.


donlowry09 Oct 2018 5:53 p.m. PST

How about the opposite chance that something unusually good could happen? Like your shot just happens to smash right through the target's co-axial MG? or causes a leak in the fuel line that sets the engine on fire -- stuff like that.

Wolfhag Supporting Member of TMP09 Oct 2018 6:47 p.m. PST

One of the Critical Hit results on the vehicle data card is hitting the coax/hull MG. I do have a crew SNAFU result for the "enemy crew chokes" with D10 turns of delay and a hit on the gun for a total of 15% of a chance for something good to happen for the shooter.

There is generally a 5% chance for a Critical Hit (greater if within Precision Aim range) when rolling for the hit location but two of the results are "round breaks up no damage" and "partial ricochet" that doubles armor protection. I don't like guarantees but I do like surprises.

I'm thinking of even doubles 5% is a shooting crew SNAFU and odd doubles 5% is a mechanical SNAFU on the target. That doubles the suspense.

Again, the % is totally subjective. There might be 50 shots in a game and 5% chance of a SNAFU is 2.5 times a game.

Again, in the game, it's not so much how many times it happens. What's important is that it hangs over the shooters and targets head each time the dice are rolled and it happens at the worst time too.


Lion in the Stars09 Oct 2018 7:49 p.m. PST

If you're only getting 50 shots off in a game, you're not shooting enough.

Infinity has critical hits. If you roll exactly the target number on the d20, that's a Crit (5% chance of crit, though if both sides roll a crit nothing happens). It's normal to roll for ~40 shots a turn. So in Infinity you normally get 2-3 Crits a player turn, 6-10 Crits a game.

And that's normal.

Wolfhag Supporting Member of TMP09 Oct 2018 11:20 p.m. PST

You have me at a disadvantage as I'm not familiar with Infinity or how it was designed but it sounds interesting.

With Infinity, 40 shots in a turn represents how much time, how many vehicles and what is the average rate of fire?

The game I'm working on is 1:1 vehicle and a battle represents about 3-5 minutes of real world time so it's a short engagement unless additional reinforcement or another wave arrives. Much of the action depends on the scenario, number of vehicles, player tactics, starting engagement range, number of guns on each side, terrain density, etc.

Some tanks never get to fire as they are ambushed or outranged and killed before they could shoot. Some spend a lot of time maneuvering before shooting. Some sit on a hill hull down and spend most of the game shooting. I don't keep track of ready rack ammo as I've found most engagements won't use up the ready ammo unless we play a larger game with multiple waves.

Once heavily engaged in a target rich environment, a tank with a 75mm gun and good crew can get off about 3-5 rounds per minute against 2-3 targets (sometimes up to 4 at short range if they are bunched up) which many people have told me is too much shooting. But when I ask them to clarify they say it does not "feel" right or it does not compare to games they play. Nothing I can do about that.

Some games have tanks shooting twice in a turn that represents up to 90 seconds. Some games the most you can shoot is 6 times because there are 6 turns. Some games the turn timing is so abstracted you can't determine or compare against historical outcomes.

It's a game, there is no right or wrong way to do it. If it feels right for you, play it. If not, find something else as there is a lot to choose from.

Using the one second turns as a timing factor I think I can better represent historical rates of fire in an engagement, including additional time spent engaging new targets and moving to a new firing position. Better crews are quicker, poor crews slower. Players can choose to shoot more quickly but with an accuracy penalty. You can't predict the exact turn of firing.

Using the timing factors there was nothing I borrowed from other games since most games are fairly heavily abstracted when it comes to rates of fire. I've had about a half-dozen Cold War and modern tank crewman play and they said it seemed about right and picked it up quickly because I use tactics and nomenclature from their manuals.

My results do compare favorably to historical outcomes and my values are mostly based on manuals, British WO reports, training standards, field testing, war and training videos, and combat AAR's. SNAFU's are designed to degrade ideal performance and have friction occur at the worst possible time when shooting.

My understanding is the Critical Hits are different than screw-ups and SNAFU's. In the Basic game, there is normally a 5% chance (roll a 20 on a D20) for a Critical Hit when rolling for hit location. However, if both shooter and target are static and within Precision Aim range (400m-800m depending on optics and magnification) you can modify the roll by a +/-4 to target weak areas or generating a 20 for a Critical Hit against the turret ring, hull MG, coax MG, cupola, etc.

I also have a former US tank/company commander with 20+ years experience helping me out that has crewed and driven T-34/85's and a German Panther and served on Patton tanks to Abrams. He's been especially helpful with the Situational Awareness factors, engagement times, crew efficiency, and the problems of observation while buttoned up.


Uncle Goblin10 Oct 2018 6:11 a.m. PST

I like this table a lot.

What's MPI?

Please keep us informed when the rules will be released. Seems very interesting.

Wolfhag Supporting Member of TMP10 Oct 2018 8:25 a.m. PST

Uncle Goblin,
MPI = Mean Point of Impact. Just think of it as accuracy.

The Advanced game gunnery system I've developed uses a formula (pre-calculated, no math involved for the player) that determines how far from the aim point (MPI) the round drifts compared to the target size/area to determine a hit. There is a version of the game that allows the player to place crosshairs over a scaled 2D image of the target and the MPI (distance from the aim point) and direction will show exactly the location hit on the target image (basically like a video game). The Basic version uses a D20 hit number like traditional games that are derived from the formula but simplified.

This weekend I'm meeting with some developers and publishers and I should have a free Basic Intro miniatures version of the game available as a free PDF download next month.

If you want a copy and sent updates email:
treadheadgames AT g m a i l DOT com

I've posted some examples of the game and historical references on Pinterest too:

You can also search TMP for "Treadheads".


emckinney10 Oct 2018 9:07 p.m. PST

Placing the cross hairs on the target is just viscerally fun :)

Wolfhag Supporting Member of TMP11 Oct 2018 3:43 p.m. PST

Here are some tankers should appreciate:

Murphy's Laws of Armor

1. Just after you report "Redcon 1" (Readiness Condition 1 – ready to move out right "now") for your qualification run, you will realize that you desperately need to take a leak.

2. The fuel truck will run out of fuel just before he gets to your tank.

2a. You will run out of fuel before he returns.

3. Tanks don't float.

4. If a supply sergeant is given a choice between death and going to the field with his unit, he will ask for a few minutes to "Think it over."

5. Attempting to help recover a mired tank will only result in your tank becoming mired also.

6. The primary purpose of an operations order is to ensure that all blame falls on the line units.

6a. For this reason, the staff will not publish an operations order until after the exercise is completed.

7. Night vision devices will only fail at night.

7a. They will function perfectly once the sun rises.

8. The dirtier and more tired you are, the less appreciative you become of "constructive criticism" from somebody in a pristine uniform.

9. The heater on your tank will fail in October. The part to repair it will arrive in April.

10. No matter how minor the ailment, a visit to the medics will result in an I.V.

10a. Arguing with the medics about this will result in your being evacuated in a neck brace and backboard (in addition to the I.V.).

11. When loading the main gun, remember: "pointy end first."

12. The only times you will throw a track (that flexible band of metal and rubber the tank travels on) are: a. At night, b. in the rain, c. during the movement back to garrison, or d. one hour after you installed the new ones.

13. Your vehicle will go NMC (Not Mission Capable – deadlined ) right after the contact team leaves the AO (Area of Operations).

14. All infantry fighting vehicles don't look alike.

15. Shaking trees to your front mean that you are being hunted by helicopters.

16. When you are told your engineer support was needed elsewhere, the bridge will be out.

17. The exercise will finish and you'll get back to garrison just after the wash rack (where tanks are cleaned) closes.

18. If all else fails, shoot at the muzzle flashes the larger ones are the dangerous ones, the smaller ones are infantry.

18a. The infantry muzzle flashes you ignore are covering an anti-tank team setting up.

19. "Rebel yells" are not proper FM radio procedure after a successful Table VIII (The tank crew qualification test a 10 engagement run on a tank range which tank crews must successfully complete in order to be a qualified crew. Like going to the rifle range for a qualification of expert) shoot.

20. XO math: 3 pacs on the ground + no fueler + 2 deadlines = 100% FMC (Fully Mission Capable).

21. Close air support is safest from far away.

22. Proving that three feet of frontal armor protection will defend against any threat is probably best demonstrated on someone else's track.

23. Hearing an "Aw, shit" soon after an "on-the-waaay!" means you're probably not getting that promotion.

24. Tanks are very easy to see unless you're dismounted and they're backing up.

25. The one time you skip the firing circuit test is when you have the misfire.

26. "GUNNER, SABOT, SNIPER" (firing an anti-tank shell at a sniper) is not an appropriate use of ammunition.

27. It is cruel to tell NBC types "Damn, that Fox (NATO chemical/biological/nuclear weapons detection vehicle) looks like a BMP (Russian made armored vehicle used by many countries, like Iraq)!" particularly when live rounds are being issued.

28. Blackout drive + autobahn + 0345 = polizei.

29. Unsecured turrets will only swing freely mid-way through a rail tunnel.

30. When doing a gunnery, the tank is always operational until you get to the ready line.

31. If you are promised "downtime," what they really mean is: You will be breaking track.

32. First sergeant math: Buy Gatorade for $1.49 USD each and sell for $1.00 USD each with the profits going to the unit fund.

Legion 412 Oct 2018 7:26 a.m. PST

Wolf once again you've done your homework ! thumbs up

Mobius Supporting Member of TMP13 Oct 2018 7:47 a.m. PST

How does the range estimation error affect the MPI?

Legion 413 Oct 2018 8:02 a.m. PST

And yes, Wolf even an old Mech guy like me can appreciate those Murphy's Laws of Armor ! evil grin

How does the range estimation error affect the MPI?
The closer the target the better the range estimation obviously. And there are some devices on AFVs, weapon systems, binos, etc. that assists in getting a good range to target. E.g. something as simple as the sight reticle markings on the lens, etc.

Lion in the Stars13 Oct 2018 8:31 a.m. PST

@Mobius: Bullets don't fly in a straight line, they fly in a 'rainbow'. The slower the bullet, the bigger the curve. HESH (or HE) flies slower than Sabot, so you have to aim higher for the same range.

Slower flight speed also impacts how much lead you need to give the target.

If you really flub your range guess (and the target is closer than you think), your shot will go over the top of the target. If you're not quite so far off, your shot will hit high.

If your range guess is that the target is closer than it actually is, your round will hit low or short.

Mobius Supporting Member of TMP13 Oct 2018 9:49 a.m. PST

@Lion. What is the equation to combine the MPI of the gun deviation with the mean range estimation?

Lion in the Stars14 Oct 2018 6:33 a.m. PST

@Mobius: an ugly one, not one that I know off the top of my head.

You see, gun deviation should be very close to a linear equation, 1/10 mil deviation at 100 yards should be putting every shot within a 10cm circle at 1,000 yards. That's very damn accurate, btw, most guns are probably closer to 1 mil, making that 10cm circle at 100m. (and trust me, you want to use mils for this equation, because 1 mil is 1m diameter of dispersion at 1000m. Easy math!)

The problem is that bullet flight is a parabolic equation due to gravity. The longer the flight the steeper the shell drops, so slower shells will drop significantly more at the same range than faster shells.

How much the shell drops varies per shell, though some WW2 guns (like the Sherman's 75mm) had pretty close matches between their AP and HE shells. But a German KwK39 (as used in Pz3 J-M and Puma armored cars) had a SprgrPtr.38 HE shell that left the muzzle at 550m/s while the PzGr40 HVAP left the muzzle at 1100m/s (and the much more common PzGr39 left the muzzle at 835m/s). So that HE shell will take at least twice as long as the HVAP shell to reach the target, which means gravity will pull it 4x farther down!

Note that those are muzzle velocities, not constant velocities. Atmospheric drag starts slowing the projectile as soon as it leaves the muzzle, but that should be a linear equation (or close to one, anyway).

There are some ballistic calculators on line, but finding one that can crunch numbers beyond 1000m/yds or that will handle cannon calibers and weights can be a challenge. The other challenge is finding the key data for the calculator, like the shell's ballistic coefficient (a function of how much drag the shell has, higher the BC the less speed it loses due to drag).

If you're OK with a Scientific Wild-Assed Guess for the equation, range estimation is a function of crew skill.
Better crews will have more accurate range guesses, less chance of completely missing the target.

The range estimation error would move the MPI up or down on the target silhouette, and ONLY up or down. If your target is closer than you think, your shot will hit high, if your target is farther than you thought your shot will hit low.

Target speed/lead estimation error would move the MPI left or right on the target silhouette. Which direction depends on relative movement of the target compared to the shooter and whether your guess was high or low. Assuming that your target is move to your left, a high guess would shift MPI left, low guess would shift MPI right. And vice versa if the target is moving to the right. That's a separate guess from range estimation.

I don't know how you'd set that up. I mean, I know how I'd set it up designing a game from the ground up, but I also want to keep everything using the same mechanics. So if you're already using 2d6 for things, I'd use 2d6 plus crew skill.

You have me at a disadvantage as I'm not familiar with Infinity or how it was designed but it sounds interesting.

With Infinity, 40 shots in a turn represents how much time, how many vehicles and what is the average rate of fire?

The game I'm working on is 1:1 vehicle and a battle represents about 3-5 minutes of real world time so it's a short engagement unless additional reinforcement or another wave arrives. Much of the action depends on the scenario, number of vehicles, player tactics, starting engagement range, number of guns on each side, terrain density, etc.

Infinity is actually an infantry game, 10-20 models per side. Mechanically, it's IGO-UGO but it has automatic reactions if one of your models can see whichever of my models is acting (you resolve one order at a time, and can spend multiple orders per model, but you only get 1 order per model in your force. 10 models on your side gives you 10 orders to spend total per turn, and that will go down as you lose models. You count orders available at the start of your active turn).

Anyway, the typical rate of fire is 3 dice for the attacker and 1 die for the defender (opposed rolls using a 'blackjack' system, get as close to your target number as possible without going over, defender is either shooting back or dodging). You can get as high as 5 dice for the attacker, but a basic rifle gets 3 dice. There are some things that can give a defender more than 1 die, and there are ways to give the defender no dice at all (or have such a penalty to their roll that they cannot succeed).

Length of time that a single turn takes isn't specified, but given how much you can do in a single order it's something like the old "I'm up, they see me, I'm down" mantra, 3-6 seconds per order. Both players have an active turn and a reactive turn, Player A is active while Player B reacts, then Player B is active while Player A reacts.

We describe an order to new players as an amount of time the 'camera' follows that model for doing something cool. There are 'Entire Order' skills that may take longer than 3-6 seconds, but I think 3-6 seconds for a quick dash of ~8m to the next cover and a burst of fire is about right.

Games are very short, tournament games (and most campaign scenarios) are only 3 turns. 10 orders per player times 6 seconds per order is one minute per active turn (and 2 minutes per round, obviously more if there are more orders to be spent), maybe 5-10 minutes of action in an entire game, tops.

Legion 414 Oct 2018 7:43 a.m. PST

What is the equation to combine the MPI of the gun deviation with the mean range estimation?
I always sucked at math ! huh? evil grin

Mobius Supporting Member of TMP14 Oct 2018 10:47 a.m. PST

The range estimation error would move the MPI up or down on the target silhouette, and ONLY up or down. If your target is closer than you think, your shot will hit high, if your target is farther than you thought your shot will hit low.

That's a good enough way if you don't want to crunch the numbers. I want numbers so I wrote my own ballistic calculator. But it uses standard deviation rather than mean deviations. You can convert one to the other if it is Gaussian.

For range estimation there is this:


Note – The reason for the mean to be 20-25% and the even chance to be 17-20% is because in a Gaussian curve the 50% zone (probable error) is 0.84535 of the mean deviation.

Wolfhag Supporting Member of TMP14 Oct 2018 11:32 p.m. PST

Mobius knows what he's talking about.

Yes, I'm in agreement with you on the vertical MPI and using mils to measure MPI distance from the center mass aim the point.

The British developed an equation for direct fire against a moving target taking into account the angle off, speed, gunner lead estimation error and the shells time of flight. I converted the equation into a table that uses three steps and then simplified it into a single table with one D20 die roll.

I've got some pretty accurate Time of Flight values (some are taken from manuals) and I have developed a formula with BRL error budget data to generate the trajectory curves using angles of descent, time of flight and base mil accuracy. I use a range estimation error of 15% for Ace crews, 20% for Veterans, 25% for Trained and 30% for Green crews. The range estimation error adds to the base MPI value before randomizing it. With my formula, I can plug in mil variables for things like aiming error (based on crew type, optics, and magnification) to generate a customized gunnery table. I'm not saying it is going to pass a physics teachers evaluation but it is playable and gives pretty good historical results with a single die roll with no die roll modifiers. I hate searching around for modifiers.

To measure the MPI of a shot by randomizing the base mil accuracy value I've been using 2D10 (1-100) but am evaluating using a D20 roll on a nomogram which people seem to like better. If the randomized MPI mil value result is <= to of the targets vertical size the round hits (this is assuming a center mass aim point). This eliminates the need for a die roll modifier for target size. Accuracy penalties (moving shooter, crew type, aim time, tactics, environmental, etc) will increase the base MPI before randomizing it as there are no die roll modifiers.

In case you are wondering: NO – I'm not using the perfect range trial results.

Realistically, against moving targets a second D20 roll is needed to determine if the lateral MPI is <= the targets horizontal size (based on angle off). I can abstract it into a single roll with the vertical size. I'm evaluating and playtesting a few different ways to get an accurate result without straining peoples brains or mine either. I'm not an engineer or math major, all values are shown already figured out.

Right now a single D20 should take care of all of the die rolls in the game. I had a statistics major and engineer evaluate the randomized results and he gave it a thumbs up.

When I explain this to people they get confused except for people with previous real-life experience as a tank crewman as most of the nomenclature and tactics are taken from their manuals. I think it's partly my fault and the fact that the game rules and mechanics bear very semblance to other games as that was my intention. After a few tries while playing it becomes pretty easy as there are no calculations other than one or two die roll modifiers because I have a customized chart for each gun and data card for each vehicle model.

The Infinity game seems OK for infantry engagements. I've not finalized anything for my infantry rules other than HHAT weapons. I'm envisioning team/section sized units. I'm evaluating using a British War Office Report for determining small arms causalities based on the volume of fire over a short period of time. There will be an immediate reaction to enemy fire. To advance under fire a unit will need to pass an Aggressiveness Check.

I developed the system to be intuitive and historical, not to torture and confuse people. ASL and Tractics is torture for me. Your knowledge of the technical aspects, manuals, and tactics of WWII tank and infantry warfare will help get you quickly up to speed. Trying to compare it to other games will most likely confuse you so the game is not to please everyone.


Lion in the Stars15 Oct 2018 6:43 p.m. PST

I had to make sure what section of the forums we were in, and where we were crossposted to when I made my comments, you get a somewhat different set of 'oops' results with Abrams and their FC computers. (example, 'gunner didn't drop old range before shooting.' 'drop' because the "hold the last range lased" switch is the rest-of-the-hand squeeze, while the lase switch is the trigger.)

Ballistics is fascinating, and all sorts of ugly math. I've taken stats (and calculus before that), so I mostly understand why it needs to be that complicated, but doing the math gives me a headache. I really need to fix that if I'm going to get into serious long-range shooting.

Wolfhag Supporting Member of TMP17 Oct 2018 9:22 a.m. PST

It's not really that difficult if I've done it (no stats and calculus courses).

You need to decide what Error Budget factors you are going to use. You'll also need the time of flight and angle of descent values.

By determining the max ordinate and angle of descent of the round you can get an idea of how the range estimation error will affect MPI accuracy.

To have an accurate system you'll have to incorporate the different fire control techniques too. A missed shot at > 1200 meters was normally a bracketing correction of 400m, at less than 1200m it was 200m. That will decrease the MPI value making it more accurate.

By assigning all of these variables a mil value you can easily get accuracy values at any range (I use 100m range increments).

There are several manuals you can find that has all of the info you'll need.

To determine a hit you can use a % chance with modifiers for target size. I determine a hit by comparing the MPI (in tenths of a meter) against the target size which is about 50% of the height of the target (that assumes a center mass aim point). If the MPI is <= the target size it hit. Accuracy penalties and poor crews use an MPI value at a longer range, not a die roll modifier. I let the player use a Risk-Reward Decision to fire sooner with an accuracy penalty which is normally a good idea if you have a muzzle velocity greater than your opponent.

I'm using a nomogram with a single D20 die roll with no modifiers to randomize the base MPI value and compare it against the target size.

There are some online calculators to get some of the values mentioned above.

Good luck,

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