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"High velocity vs low velocity high explosive shells" Topic


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743 hits since 16 Oct 2018
©1994-2018 Bill Armintrout
Comments or corrections?

Simo Hayha17 Oct 2018 4:49 p.m. PST

How much did the velocity of the gun alter high explosive effectiveness?

Is it that the shell digs too far into the ground that lowers high velocity effectiveness?

Is it worth modeling in a game?

Personal logo optional field Supporting Member of TMP17 Oct 2018 5:08 p.m. PST

High velocity shells require thicker shell walls to withstand the higher acceleration. So for a given size, there's more shell wall and less explosive filler.

Lee49417 Oct 2018 7:37 p.m. PST

In addition to thicker shell casings higher velocity shells often cause larger muzzle blasts which kick up dust and dirt and make adjusting for subsequent shots difficult. The US Sherman 76 especially had this problem. Further, some early war high velocity guns were not provided with HE rounds, or had very ineffective HE due to very small explosive fillers. And yes all of this is modeled in my rules. Cheers!

Wolfhag17 Oct 2018 8:24 p.m. PST

Here is the best example I have:

picture

The rules I'm using with 1" = 25m so I can accommodate these tactics. The US Shermans HE rounds had a delay of .005 seconds allowing the best height for an air burst. The Germans delay was .01 seconds which put the round too high for an effective air burst. The thinner walled shells allowed more explosive.

Some tanks had their HE shells traveling at a slower velocity then AP rounds. Even though the HE muzzle velocity was slower it had the effect of a greater angle of descent which actually made it more accurate firing at a point on the ground against targets at ground level and infantry. Also, firing delay fuse HE into a tree line will allow some penetration and an air burst.

I use the amount of HE filler to determine damage as shell diameter alone is not a measure of HE effectiveness. Some US units in Europe still preferred the short 75mm (1.7bs) on the Sherman rather than the 76mm (0.9 lbs) high velocity for the reasons above.

Wolfhag

Martin Rapier17 Oct 2018 10:25 p.m. PST

The main determinant of HE effectiveness is filler weight, HV rounds tend to have thicker casing and less filler.

In terms of effect, the War Office found that 76mm HE was approximately 30% less effective than 75mm HE. The helpful suggestion was to just fire more shells at the target…

Id suggest that this stuff is only worth modelling if you track each shell fired, or it an be factored into firepower ratings in higher level games.

goragrad17 Oct 2018 10:34 p.m. PST

One reason the German heavy tank companies in WWII were equipped with a mix of PzIIIN and Tigers was the greater effectiveness of the 75L24 when firing HE.

As noted by Wolfhag the greater angle of descent improved the chances of hitting ground level point targets such as infantry and AT positions. There is also the fact that a near miss may still catch at least part of the target in the blast or fragmentation.

A high velocity round with a flatter trajectory might not hit the ground for quite a distance with a 'near miss.'

Griefbringer18 Oct 2018 1:05 a.m. PST

One reason the German heavy tank companies in WWII were equipped with a mix of PzIIIN and Tigers was the greater effectiveness of the 75L24 when firing HE.

Interesting to hear that – I had always thought it was just a temporary workaround to fill the formations until sufficient numbers of Tigers became available.

Martin Rapier18 Oct 2018 2:06 a.m. PST

I think the Pz IIIs were just there to bulk out the numbers. The Tigers HE round was pretty effective (just what you need in a 'breakthrough tank'). It had 0.9kg of HE, more than a Shermans 75mm.

The 75mm on the Pz III only had 0.45kg of HE.

langobard Supporting Member of TMP18 Oct 2018 3:03 a.m. PST

+1 Goragrad. I have had it in my head for years, if not decades that the reason the early Tiger companies had a mix of PzIIN and Tigers was so the escort IIIN's could deal with infantry / AT threats with their 75's.

Of course, this could be a wargaming myth (it irks me that I "know" it, but cannot for the life of me remember the source) but I'd be interested in anyone elses thoughts.

deephorse18 Oct 2018 3:33 a.m. PST

The Panzer III was present in early Tiger units because insufficient Tigers had been made and delivered to those units.

‘Tigers in Combat vol. 3' by Schneider

Mobius18 Oct 2018 3:33 a.m. PST

The blast pattern of an HE shells are pretty strange. Around 30 degrees and more is mostly from the shell walls and spreads perpendicular from the shell path. At near 0 degrees it spreads from the shell walls and from the shell nose and base like a cross. But to impact at 30 degrees even a slow 75mm HE would have to travel 10,000 yards. For a game the blast pattern shouldn't matter.

One thing about HE shells accuracy almost no one takes into account is that they did not have tracers. So if they are too fast or the light is poor the TC or gunner could not track them. They do let the gunner know where they land.

Fred Cartwright18 Oct 2018 4:00 a.m. PST

Yes the Tiger I's 88mm gun has effective HE. It was, after all, developed from the flak gun and you need good shell fragmentation on AA shells.

Skarper18 Oct 2018 5:06 a.m. PST

There was no smoke shell for the 88mm iirc. That would make the 75mm L24 very useful. Plus, the Tigers would want to be carrying more AP as the war went on.

But, I suspect the PzIIINs were there mainly to make up the numbers. Another logistical headache to contend with. Hence the marginal value they brought was dispensed with.

I distinguish between low and high velocity guns in my own rules for HE effectiveness. I suspect I exagerate it for flavour.

In the case of mortars, a small calibre bomb has more punch than the equivalent weight gun shells. Or so I have read somewhere.

I think it matters in games where one vehicle is one model…but in larger level games I would factor it in to combat stats.

emckinney18 Oct 2018 7:30 a.m. PST

The flatter the trajectory, the harder it is to hit horizontal, "single range" targets like foxholes. A very small error in elevation causes a large change in impact location in range. While the high/low velocity difference vanishes at short range, it becomes dramatic as the range gets long.

There are also problem hitting targets on a crest. A tiny bit high and the shell goes over the crest and misses completely! Low, and the slope absorbs any fragments thrown forward.

On the other hand, velocity has almost no effect on hitting vertical targets like buildings and bunkers, or even stone walls. High velocity is better if you're trying to get a shell through a window or embrasure.

The distinction between horizontal and vertical targets is very important, but I've never seen it reflected in rules (I believe it's modelled in some computer wargames).

DeRuyter18 Oct 2018 8:54 a.m. PST

The Pz III N was replaced by the halftrack variant with the 75mm L24 in the HQ Co. of the Tiger battalions. Apparently not all the Tiger commanders were happy about the TO&E change as the Pz III was useful as anti-infantry protect. They also allowed the Tigers to carry more AP rounds.

Wolfhag18 Oct 2018 2:47 p.m. PST

(I found this on another website) Firing HE at a ground point target at 800m. 75L24 MV is 450m/s and the 75L70 is 700m/s. The 75L254 has a descent angle of about 1.5 degrees. The 75L70 is about 0.5 degrees. If the vertical dispersion is 1.0m on flat ground the 75L24 is off by 40m and the 75L70 is off by 120m. A higher percentage of the 75L24 rounds will land closer to do damage. Steeper angles of descent will give a closer bracketing on the ground (horizontal) targets but not in the vertical targets when firing at vehicles. so 75L24 HE had 30% more bursting explosive than 75L70.

emckenny,
That's interesting about the crest, I never considered it. The horizontal dispersion should also be less if the shooter is at a higher elevation than the target.

In the game you played using the detailed hit location, you can determine how far above ground level the round is when missing or hitting. I'll have a separate target booklet to shoot at scaled images of MG emplacements, pillboxes, bunkers, etc. But when firing at an infantry team target you need to hit a point on the ground.

I have an extra row on my gunnery charts (in 100m increments) for the 75L24 gun that would show that for every 0.1m the round is above ground level how far it would travel. At 800m with an AOD of 1.5 degrees the round will travel 3.8m for every 0.1m, it is above the ground at 800m. So if 1.0m vertical dispersion you get 38m (the above example shows 40m).

As long as you have the AOD you can figure it out. However, making it playable and worthwhile to use is something else. I have not playtested it yet but it does seem to have possibilities against infantry and emplaced anti-tank guns. Using the above example, a 0.5m vertical error would still hit an emplaced anti-tank gun, emplaced machine gun or a small bunker. A 75mm HE round impacting 20m-40m in front or behind emplaced guns or infantry isn't going to have much of a causality effect.

I recall a German tactic of a StuG with a 75L24 standing off at 2000m and firing at fixed defenses and emplacements. If the AOD is 5 degrees (approximation) 1.0m vertical dispersion will put the round an additional 14m. Longer range equals closer grouping over the ground, that's the advantage the short barrel has. Since the HE shell burst pattern is mostly perpendicular to the shell path like Mobius said, it appears you need to get pretty close to the target and those pie-shaped burst patterns are not accurate for plotting single rounds.

picture

Wolfhag

langobard Supporting Member of TMP18 Oct 2018 4:24 p.m. PST

@Deephorse. That is good enough for me. Wargamer myths are interesting beasts!

Mobius18 Oct 2018 7:05 p.m. PST

The vertical dispersion of the 75mm/L24 is about 1.5x that of the 75mm/L70 at 800m. A .01° change in elevation of the L24 is off by 5m at that range while a .01° change is off by 15m in range for the L70.

Lion in the Stars19 Oct 2018 6:23 p.m. PST

Down at the smaller end, the 5cm KwK39's HE shell was only 550m/s while the PzGr40 was 1100m/s.

Legion 420 Oct 2018 7:47 a.m. PST

Some good comments here. My Short simplistic answer:

Low velocity is good for killing unarmored targets, e.g. Infantry, trucks, etc.

High velocity is good for killing armored targets.

I.e.

The Pz III N was replaced by the halftrack variant with the 75mm L24 in the HQ Co. of the Tiger battalions. Apparently not all the Tiger commanders were happy about the TO&E change as the Pz III was useful as anti-infantry protect. They also allowed the Tigers to carry more AP rounds.

But again my comment is a bit simplistic generally …

However to muddy the waters a little, as some have noted, e.g. in 1940, a Panzer IV with the short barreled L24 75mm could still generally take out most allied armor/AFVs. As their armor was a bit thin, save for e.g. the UK Matilda …


For gaming purposes:

A Low velocity HE shell has a burst radius/Blast Template …

A High velocity HE gets no or a much smaller Blast template …

Wolfhag20 Oct 2018 2:37 p.m. PST

To complicate matters the 75L24 HEAT/HE round MV was 450m/s and the AP was 385m/s. I think the reason was the AP round weighted 6.8kg and the HEAT/HE was 4.5kg. The casing for the 75L24 was very short so they probably could not get more propellant in for the AP round and did not want less for the HEAT/HE round. I think it also fired a canister round too.

Wolfhag

Legion 420 Oct 2018 2:45 p.m. PST

Interesting … and again, yes as we know in the early battles of WWII the 75L24 could KO many/most of the AFVs in the Allied inventory.

Andy ONeill20 Oct 2018 2:52 p.m. PST

The wiki article on the 75 l24 is pretty good.
link

Legion 420 Oct 2018 2:54 p.m. PST

Interesting … yes as we know in the early battles of WWII the 75L24 could KO many/most of the AFVs in the Allied inventory.

Legion 421 Oct 2018 6:14 a.m. PST

How'd I get a double post ? Again ? huh?

Wolfhag21 Oct 2018 6:28 a.m. PST

Legion,
You need to go back on your meds dude before you hurt yourself.

Wolfhag

Legion 422 Oct 2018 6:28 a.m. PST

Too late !!!! huh?

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