"57mm and 6lb AT guns - ammo interchangeable?" Topic

Doing some research into the 57mm/6lb AT gun.

Was the ammo interchangeable?

I read that the British 6lb AT fired a 57mm x 441mm shell, but haven't been able to find anything on the US gun other than it was 57mm in cal.

Soviet 57mm used a longer shell, so those are NOT interchangeable.

What I've found is the US basically copied the British 6lb gun with changes to carriage and gun shield being the major changes, but not so much to the actual gun.

I've seen them in both British and US service with and without muzzle breaks.

I have read that the US airborne took the British 6lb AT (airborne version, shorter wheel axis and barrel to fit in gliders) from Normandy on, but have only read that at one site.

So, kinda like the old mustard commercials, could a Yank say to a Tommy:

"Do you have any 57mm AT ammo?"

Tommy:

"But of course, AP or APDS?"

Thanks in advance.

US forces drew upon UK stocks of HE after D Day so that would suggest they were interchangeable. That proably also went for 6pdrs in Russian service (for example on the T48 / SU-57 GMC) but not indigenous Russian designs

The us 57mm breech, barrel and parts significant to this question were the same as the 6pdr.
Because developing a round is non trivial.

The soviet 57mm was not a copy so was 57 mm only because that's a known calibre tracing it's origins to black powder cannon firing spherical iron balls. 6pdr weight driving the diameter.

That's my understanding anyhow.

The US 57-mm M1 was derived from the British 6-pdr, though the US made various changes to the carriage, resulting in something different from the British version.

The US Army Catalog of Standard Ordnance items only covers the gun briefly, no mention of amn being the same as the British. 57-mm amn is listed as the M70 AP (substitute standard) and M86 APC (standard). Again no mention on these being exactly the same as British rounds.

I feel I should be able to offer something more concrete on the dimensions and weights of the 6-pdr rounds but can't offhand. The US rounds are given as 12.82-lbs for the M70 and 13.88-lbs for the M86, both weights for a complete round.

It did remind me of an old post on TMP re the 57-mm gun, and something about US guns having a longer barrel that us Brits couldn't provide. Cue cartoon images of workmen with tape measures and puzzled expressions. I did have a look at the time, and the first 6-pdrs into British and Commonwealth hands in the desert did have a shorter barrel. This was an expediency to get guns to the troops while manufacturing facilities were being expanded, and subsequent 6-pdrs had a longer barrel length.

I did think that was what the claim was based on, sort of right for 1942 but incorrect thereafter. I did find something though on US 57-mm guns having a longer barrel than later 6-pdrs, which isn't really obvious from contemporary ordnance info. The Catalog just says the barrel was 50 calibres.

Gary

The US 57mm anti tank gun was the British 6lb anti tank gun produced uneder license in the US. Ammo was totally interchangeable.

The only point folks failed to mention is that the US tended to have the 57mm built with the barrel approximately a foot linger, due to the fact the most machinery lathe euqipment the US had was longer. The initial UK specs as designed, could not be built to the exact length as designed in the UK as the length of the lathes were a bit too short on average. Not a problem when the designs were looked at in the US.

Ruskie 57mm,,,an entirely different beast.

The soviet 57mm was not a copy so was 57 mm only because that's a known calibre tracing it's origins to black powder cannon firing spherical iron balls. 6pdr weight driving the diameter.

No, the 57mm derives from the late 19th Century 6-pdr quick firer. The bore of the old 6-pdr smoothbore was 88-90mm, depending on whose pound was used.

Doing some research into the 57mm/6lb AT gun.

It's "pdr" (NOT "lb", "lber", "6#", Royale with Cheese, etc, etc).

To the question, something that regularly comes up is whether the US had limited stock of 6pdr APDS that could be fired from US 57mm ATG. eg:
TMP link

Interesting discussion. I had thought 8th Army 6pdrs were shorter due to lacking muzzle break… but tooling ability could be correct.
Explains why some models have longer barrels than others!

Yes. Most tooling that could do longer barrels were rather busy with longer guns or naval guns.

I had a look through the Canadian online reels and oddly enough couldn't find a straightforward 'contemporary' set of stats for the 6-pdr. It did confirm there was a difference in barrel length between the MkII and MkIV versions of the gun, the latter being 16-inches longer. RA Notes of February 1943 reported that production had gone over fully to the MkIV at that date, so the MkII was eclipsed fairly quickly.

The old 'British and American tanks of World War Two' (Chamberlain and Ellis) gives barrel lengths for the tank mounted versions, with 96.2-in for the MkIII and 112.2-in for the MkV, which shows the same 16-in differential. If the US M1 57-mm did have a barrel length of 50 calibres, that would actually work out to 112.2-in wouldn't it (2850mm)? So the same as the British MkIV on carriage and MkV in tank?

Gary

I managed to find a scan of TM 9-303, the tech manual on the M1 57-mm. Barrel length was 112.2-in, same as the British MkV in tank, which should also be the same for the MkIV on carriage. So the US gun was the same dimension as the British one, excepting the early MkII and MkIII 6-pdrs of 1942, which were superseded in production from the start of 1943.

link

OK, slightly confused by all this analysis of barrel lengths.

The question is whether the ammo was interchangeable. Doesn't that come down to whether the breach chambering was the same – nothing to do with the actual barrel lengths in calibres, inches, mm, whatever…?

The longer barrel would presumably improve AP performance versus the same round out of a shorter barrel.

Sorry, the sidetrack re barrel length was mine. I was trying to work out what the perception that the M1 57-mm had a longer barrel (and therefore improved performance over) the British 6-pdr it was based on. Answer – only an improved performance over the MkII 6-pdr, which was quickly superseded by the MkIV in British use, with the M1 and MkIV having identical barrel length. The RA Notes reckoned the 16-in longer barrel of the MkIV gave around 150 foot per sec extra velocity on the MkII.

If the gun was identical (as in breech and barrel noted above) the amn should be interchangeable. Sadly I'm not aware of a single source for various stats on British field artillery equipments that would describe the British amn in the same detail as US publications do the M70 and M86 rounds.

What I have noticed in reading RA documents (though admittedly much of the technical blurb is well beyond me) is that the impact of firing various types of exotic AP rounds down the 6-pdr did come with a downside in terms of barrel wear and need for de-coppering. The US 57-mm may have been able to fire the same suite of amn but it could have an effect on the gun not seen with the standard US rounds.

Gary

See
link

See
link

Yes, this is the APDS story again (per the link I posted above, before that one veered off the topic).

I had forgotten that this question of interchange of ammo also arises in relation to HE.

P.S. Jeff Duquette used to post on quite a few forums but I haven't noticed him around for a while…

Now that my memory has been prodded a bit, I think this idea of the 57mm / 6pdr ammo swap might have come up in relation to ASL. You know how much that game loves obscure WW2 factoids…

Anyway, I'll have a dig around later to see whether I have retained any notes on the subject…

OK, here's a bit of info…

First following up on the ASL side of things I found an old table which lists for "M1 57mm AT Gun" the ammo available being:
HE7J4E/75, D4J4+E
(that doesn't transfer too well here – some of it is superscripted)

Without delving into what all that gobbledy gook actually means re availability dates, etc, they clearly thought some kind of HE round was available. Which would presumably be British 6pdr ammo…?

Alright, not a primary source yet for HE.

But more promising on the APDS front.

WO 219/2806, Appendix G to SHAEF/16652/GCT/Arty
Dated 11 July 1944. "Perforation of homo at 30º Strike", ranges in yards.

Next to 6pdr "SABOT" (ie APDS) there is a footnote "(b)" which further down under Notes says:
"(b) Fits US 57mm"

I'm not 100% sure HE was British only. I thought so and the "overseas" rounds supplied to britain do not include an HE round.

Remember that the US made some 6pdr and ammo for the British.

It seems a bit odd they bothered to make hardly any adaptations for their own "57mm" version but NIH does funny things to otherwise sensible people.

It'd be a big deal to invent a different shaped round.
I'm certain about APDS.
APDS was british manufacture only and somehow fitted.

I did have a scrabble about but can only find a few fragments.

The two US field manuals on Organization, Technical and Logistical Data give proportion of ammunition types for the 57-mm gun.

October 1943 was 100% AP

August 1945 was 70% APC, 15% HE and 15% cannister

Some stats on the amn of various types of British artillery equipment are randomly included in one of the files here;

link

The figures are not a match for those given for the US M70 and M86 rounds (12.82-lbs for the M70 and 13.88-lbs for the M86, both weights for a complete round).

And some pics of British 6-pdr rounds can be seen here;

quarryhs.co.uk/Molins.htm

Gary

Sadly I'm not aware of a single source for various stats on British field artillery equipments that would describe the British amn in the same detail as US publications do the M70 and M86 rounds.

Exactly. I have the US Standard Ordnance Catalog too and it gives chapter and verse on the 57mm AP (M70) and APC (M86). But (by omission) that same publication implies that these were the ONLY rounds that were standardised (by the US) for the 57mm ATG. Which certainly accords with other books I quickly checked including Encyclopedia of Infantry Weapons of WWII (Hogg) and Allied Artillery of WW2 (Hogg).

But now you've thrown cannister into the mix as well…!

What sort of range and effect would 6-pdr canister have? Would you treat it like machine-gun fire and roll for effect, or what?

They only started making cannister in January 1945 and it would have to travel.

Is that 6pdr canister from January 11945, or canister generally?

What sort of range and effect would 6-pdr canister have?

Sounds like a huge shotgun to me! I presume that the range would be a a couple of hundred meters.

In the Pacific, the US forces used 37 mm canister shot in their anti-tank guns against Japanese infantry attacks in relaticely close terrain.

37mm canister rounds were still in US use as late as Okinawa.

B

T17 m305 went into production January 1945.

link

Good find Andy.

That seems to confirm that most of the supposed 57mm HE was indeed borrowed British (6pdr) ammo.

And the "T" numbers on the US homegrown 57mm HE and also canister rounds possibly explains their absence from the ordnance catalog – it sounds like they didn't receive their "M" numbers until very late in the piece and looks like they missed whatever date was taken as the cut off for the widely available published version for WWII.

Clearly, the rounds were compatible.
They used british he and apds in us 57mm. That means other rounds would fit. Because those significant parts of the breech, barrel etc were the same.

And use of cannister seems to be approaching zero. Maybe actually zero.

Clearly, the rounds were compatible.

I agree…

And use of cannister seems to be approaching zero. Maybe actually zero.

I'd only ever heard of the US actually using that type of round in the POA with the 37mm (as was mentioned above).

I suspect the 57-mm cannister was primarily intended for use again the Japanese, I can't see it being a necessity for US forces in Europe. Marine Infantry Regiments used the M3 37-mm anti-tank gun throughout the campaign in the Pacific, and seemed to have had cannister available for it from 1943 at least. The only other figures I could find for 57-mm amn types are from a couple of CinCPOA Units of Fire, so particular to the Pacific Oceans Area.

March 1944

37-mm Tk or AT – 40 AP, 40 HE and 20 cannister (total 100)
57-mm AT – 90 AP (total 90)

Undated (marked as Revised UoF, I think probably early 1945)

37-mm Tk or AT – 30 AP, 40 HE, 30 cannister (total 100)
57-mm AT – 40 AP, 30 HE, 20 cannister (total 90)

From memory the US Infantry Regiments involved in amphibious landings modified their standard T/O and replaced the authorised 57-mm guns with either 37-mm guns (easier to handle out of landing craft and LVTs) or some form of SP equipment, I think one Div used the M8 (I've probably posted that before but forget where…).

Gary

I'm not sure how close theory was to practice on loadouts.
In theory 85% ap, 10% he and 5% cannister in sicily 1943.
Two of those didn't exist.