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Armor/AFV: Axis - WWII
Armor and ground forces of the Axis forces during World War II.
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Rechambered Pak 36 (r)
smorko
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Serbia & Montenegro
Joined: March 11, 2013
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Posted: Thursday, March 09, 2017 - 07:38 PM GMT+7
Hi guys,

Wanted to ask a very general question, because I don't quite get the rechambering of the 7,62 soviet F-22 guns to german 7,5cm rounds. I understand the chamber was rebored for a bigger cartridge, but the shell would be smaller, and that means that the propellant charge would be wasted because a portion would pass around the shell. This always bothered me.
A couple of days ago I was reading a book about automatic rifles of WWII, and it mentioned the 7,5mm cartridge used in StG 44 was directly copied to be a 7,62 russian cartridge used in AK-47. The reason for the difference in caliber was stated to be the fact germans measured the bullet size, and the russians measured the bore size. Was this true for AT guns as well? Was a Pak 40 actually a 7,62 gun? Couldn't find the answer online.
wanagun
#145
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Indiana, United States
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Posted: Friday, March 10, 2017 - 01:28 AM GMT+7
As far as measurement goes in small arms. The US, and germany i belive,measures to the groove (larger diameter) soviets measure to the land (smaller diameter). So a 7.62 30 cal bullet in the US diameter is 7.62mm or 308 but in Russia a 7.62 bullet is really 7.8 to 7.9mm or 310 to 311 calibure. Im not sure if the same is ture in cannons but it seems to if the cannon was german 7.5 going to russian 7.62 then the chamber and barrel would need to be drilled out larger. The 7.62x39 round is almost an identical copy of the German 8x33 round for the Stg 44. I belive but wont swear that the case is nearly identical and the difference is due to the bullet.
KurtLaughlin
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Posted: Friday, March 10, 2017 - 04:14 AM GMT+7
First off, the MKb 42 and subsequent weapons were 7.92mm, not 7.5mm or 8mm. Secondly, the cartridge case is 33mm long while the case used in the SKS-45 and subsequent weapons is 39mm long (measured the same way). The base and shoulder diameters are different as well. Clearly they are not interchangeable.





Lastly, the 7.92x33 Kurz round used a 8.22 diameter bullet while the 7.63x39 used a 7.92 diameter bullet. My guess is that both countries designated their calibers the same way, that is, the size of the pin that would fit in the barrel.

KL
smorko
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Serbia & Montenegro
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Posted: Friday, March 10, 2017 - 04:43 AM GMT+7
You're right I quoted the book wrong. They said the 7,75x39mm Kurzpatrone was essentially the same as the soviet 7,62x39mm, with same measurements. I thought the russian round gave the bigger measurement. But still, how was a Pak 36(r) capable of firing a smaller round? Since all AT guns relied on great muzzle velocity, wouldn't the diference in calibres decrease the effectiveness.?
Oelfass
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Hessen, Germany
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Posted: Friday, March 10, 2017 - 06:45 AM GMT+7
Concerning the rebuilt F-22 guns named Pak 36(r), these actually used 7,62 cm projectiles mounted on the cartridge of the Pak 40. The Germans produced their own 7.62 cm ammo which was different from Pak 40 shells. Those for 7.62 cm had a white tip to prevent confusion. It was probably possible to fire Pak 40 ammo in the Pak 36(r) with some loss of power and accuracy, but the other way around would have been very dangerous.

To make things a little more confusing, the Germans also used the F-22 with the modified shield and controls of the Pak 36(r), but with its original Soviet ammunition, this version was named Feldkanone (FK) 36(r).
25PDRFG
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Posted: Friday, March 10, 2017 - 11:29 AM GMT+7
Probably
wont help but the AK47 could fire N.A.T.O. 7.62 but the British S.L.R could not fire the soviet rounds
KurtLaughlin
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Posted: Friday, March 10, 2017 - 11:44 AM GMT+7

Quoted Text

Probably
wont help but the AK47 could fire N.A.T.O. 7.62 but the British S.L.R could not fire the soviet rounds



While it it possible to fire the wrong ammunition in a weapon the results can be lethal - to the one pulling the trigger.

The NATO 7.62x51 cartridge case was one-half inch longer than the Soviet 7.62x39. There is no way a Kalashnikov bolt could even close on a NATO round, let alone allow the hammer to drop and hit the bolt. A floating firing pin without a retracting spring could hit the primer in the process of moving forward (should some moron attempt releasing the bolt carrier) but with the cartridge base sticking out of the breech the result would be an explosion.

Likewise, it is correct that a Soviet round would not fire in a NATO chambered weapon because the primer would be a half inch into the chamber.

KL
Scarred
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Posted: Friday, March 10, 2017 - 04:05 PM GMT+7

Quoted Text


Quoted Text

Probably
wont help but the AK47 could fire N.A.T.O. 7.62 but the British S.L.R could not fire the soviet rounds



While it it possible to fire the wrong ammunition in a weapon the results can be lethal - to the one pulling the trigger.

The NATO 7.62x51 cartridge case was one-half inch longer than the Soviet 7.62x39. There is no way a Kalashnikov bolt could even close on a NATO round, let alone allow the hammer to drop and hit the bolt. A floating firing pin without a retracting spring could hit the primer in the process of moving forward (should some moron attempt releasing the bolt carrier) but with the cartridge base sticking out of the breech the result would be an explosion.

Likewise, it is correct that a Soviet round would not fire in a NATO chambered weapon because the primer would be a half inch into the chamber.

KL



I've owned two 7.62x51 Nato M1 Garands and a 7.62x39 Hungarian SA-85M (AK clone) with a folding stock and I can tell you first hand that you CANNOT put a 7.62 Nato in an AK or vise versa. Anyone who has told you that you can knows absolutely nothing about firearms. Anyone who has tried it and says it works has either lied, destroyed their weapon or been killed. You can't put a M16 round in an AK either.
smorko
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Serbia & Montenegro
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Posted: Saturday, March 11, 2017 - 06:52 AM GMT+7

Quoted Text

Concerning the rebuilt F-22 guns named Pak 36(r), these actually used 7,62 cm projectiles mounted on the cartridge of the Pak 40. The Germans produced their own 7.62 cm ammo which was different from Pak 40 shells. Those for 7.62 cm had a white tip to prevent confusion. It was probably possible to fire Pak 40 ammo in the Pak 36(r) with some loss of power and accuracy, but the other way around would have been very dangerous.

To make things a little more confusing, the Germans also used the F-22 with the modified shield and controls of the Pak 36(r), but with its original Soviet ammunition, this version was named Feldkanone (FK) 36(r).



Thanks, this was the info I needed, it finally makes sense.
brentwal
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Posted: Saturday, March 11, 2017 - 08:31 AM GMT+7

Quoted Text

Probably
wont help but the AK47 could fire N.A.T.O. 7.62 but the British S.L.R could not fire the soviet rounds



Just BS rumor that even predates the Internet. Pick two similar calibers and one gun can "Safely" fire both but the other (usually your countries) can only fire one.

For example, I've heard said a 98 Mauser can camber & safely fire both 8mm Mauser and .30-06, but no .30-06 chambered rifle can fire 8mm Mauser. the truth is the 8mm Mauser cambered rifle could never chamber the .30-06 cartridge which is 6mm/1/4" longer, with out the use of a hammer. But the 8mm can be chambered into the longer chamber of the .30-06 rifle and fired, but will cause damage to the rifle and shooter. On the other hand firing a 7mm Mauser cartridge out of a .30-06 is far less catastrophic.

This has been a public service message.

:-H
Das_Abteilung
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United Kingdom
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Posted: Saturday, March 11, 2017 - 11:55 PM GMT+7
Philipp, you seem to know the ammunition story for this gun: the original question. Did the Germans tool for new shell castings or did they simply use PaK40 shells with an enlarged driving band and/or select castings at the upper limit of dimensional tolerance (or even out of PaK40 tolerance)?

I understand the rechambering for the cartridge as they were in full production of PaK40 ammunition and a new case design would have been very disruptive. It just seems logical that they might also simply have adapted the existing shell castings too. An enlarged driving band would solve the obturation issue but I have no clear idea of the effect on the shell ballistics of the potentially slightly looser fitting of the shell itself. Reduced friction could actually be beneficial to intial muzzle velocity, but less energy might be imparted to the round with consequent greater energy and velocity drop-off at range
iguanac
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Belgrade, Serbia & Montenegro
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Posted: Sunday, March 12, 2017 - 02:16 AM GMT+7

Quoted Text

Probably
wont help but the AK47 could fire N.A.T.O. 7.62 but the British S.L.R could not fire the soviet rounds


This might be true of a AK47 derivative - Yugoslav M77 rifle that is chambered for NATO 7,62mm
http://www.zastava-arms.rs/en/militaryproduct/assault-rifle-m77-b1
Scarred
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Posted: Sunday, March 12, 2017 - 03:38 AM GMT+7

Quoted Text


Quoted Text

Probably
wont help but the AK47 could fire N.A.T.O. 7.62 but the British S.L.R could not fire the soviet rounds


This might be true of a AK47 derivative - Yugoslav M77 rifle that is chambered for NATO 7,62mm
http://www.zastava-arms.rs/en/militaryproduct/assault-rifle-m77-b1



And I shot AR-15's chambered for 7.62x39 and 7.62 NATO, but the myths surrounding the AK47 get to be absurd.
Oelfass
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Hessen, Germany
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Posted: Sunday, March 12, 2017 - 04:33 AM GMT+7

Quoted Text

Philipp, you seem to know the ammunition story for this gun: the original question. Did the Germans tool for new shell castings or did they simply use PaK40 shells with an enlarged driving band and/or select castings at the upper limit of dimensional tolerance (or even out of PaK40 tolerance)?



Hi Peter,

Regrettably I don't know the answer to that. I only did a little research on the Pak 36(r) since I was building a Marder III with this gun and had to look up the proper ammo for it.

I did further research but regrettably couldn't find any diagrams with dimensions in the official field manuals for Pak 40 and Pak 36(r) ammo. However, in some of the cross section diagrams the projectiles look quite different. At least the detonators and cartridges were identical. Maybe the different barrel geometry required a new type of projectile.

Here are the scans of the field manuals, in case someone else has more insights:
Pak 40

Pak 36(r)
KurtLaughlin
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Posted: Sunday, March 12, 2017 - 04:47 AM GMT+7

Quoted Text

Philipp, you seem to know the ammunition story for this gun: the original question. Did the Germans tool for new shell castings or did they simply use PaK40 shells with an enlarged driving band and/or select castings at the upper limit of dimensional tolerance (or even out of PaK40 tolerance)?



I assume here you mean casings, not castings - the Germans did not make new breech rings of blocks to my knowledge, and projectiles were normally forgings, not castings.

The German round was significantly longer than the Russian one; I've read it described as "almost twice as long"; so the breech end had to be completely re-machined internally, thus it could be whatever size or tolerance the Germans wanted.

According to Hogg's German Artillery of World War Two, the Pak39(r) used standard Pak40, 7.5cm cartridge cases. (However, in tables elsewhere in the book Hogg gives different rim and mouth diameters for the 7.62cm case.) The projectiles are listed as 7.62cm, so clearly they were different than Pak40 projectiles.

A (maddeningly incomplete) wartime US enemy ordnance catalog lists the Soviet gun with a 76.2mm bore and 0.84mm deep grooves while the few German "7.5cm" German weapons are listed with a 75mm bore.

My guess is that the guns (F-22 and Pak40) truly did have different bores and that the Germans made specific ammunition for the Soviet guns when they converted them; as Philipp wrote originally.

KL
KurtLaughlin
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Posted: Sunday, March 12, 2017 - 05:03 AM GMT+7

Quoted Text

Here are the scans of the field manuals, in case someone else has more insights:
Pak 40

Pak 36(r)



That's the answer right there, Philipp. Both manuals have illustrations of the ammunition used in the guns. The Pak40 projectiles have a bourrelet that measures 74.85mm while on the Pak36(r) it measures 76.1mm. The bourrelet is machined into the steel body of the shell and rides in the bore - it does not compress or deform.



KL
Oelfass
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Hessen, Germany
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Posted: Sunday, March 12, 2017 - 06:04 AM GMT+7
Thank you Kurt, I completely missed that!
ALBOWIE
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Posted: Sunday, March 12, 2017 - 09:46 AM GMT+7

Quoted Text

Probably
wont help but the AK47 could fire N.A.T.O. 7.62 but the British S.L.R could not fire the soviet rounds



There is no way a 7.62 x 51 (NATO as used by the L1A1 SLR) could be chambered and fired in a 7.62 x 39 AK 47. This is an old wifes/squaddies tale and one I have seen debunked personally by my Pl SGT.
Where this story probably got its basis is that the Chinese Communists initially copied a lot of US Weapons in hte 40's but made them slightly larger in in bore so that they could use captured Ammo from the Nationalists but not vice versa although I have read this in many books on Small arms this may well be another old wives tale
Al
Arte Et Marte
KurtLaughlin
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Posted: Sunday, March 12, 2017 - 12:25 PM GMT+7
Al, in the USA at least, the origin was a way of explaining why the .30-06 round was replaced by the 7.62 NATO - So NATO and Russian guns could use the same ammo!

KL
trickymissfit
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Posted: Wednesday, March 15, 2017 - 07:07 AM GMT+7

Quoted Text

Hi guys,

Wanted to ask a very general question, because I don't quite get the rechambering of the 7,62 soviet F-22 guns to german 7,5cm rounds. I understand the chamber was rebored for a bigger cartridge, but the shell would be smaller, and that means that the propellant charge would be wasted because a portion would pass around the shell. This always bothered me.
A couple of days ago I was reading a book about automatic rifles of WWII, and it mentioned the 7,5mm cartridge used in StG 44 was directly copied to be a 7,62 russian cartridge used in AK-47. The reason for the difference in caliber was stated to be the fact germans measured the bullet size, and the russians measured the bore size. Was this true for AT guns as well? Was a Pak 40 actually a 7,62 gun? Couldn't find the answer online.



The Germans measured the O.D. of the projectile differently (actually bore I.D.) than the Soviets. One measured from the diameter of the lands, while the other went by the diameter of the grooves. An example is the AK 47 round being .311" in diameter while a typical U.S. 30 caliber round is .308. Yet both are listed as 7.62 mm in diameter.
An artillery round works off a driving band to seat into the rifling. They could correct this with a larger driving band, or go with a larger projectile. I seriously doubt there's much difference between the two bores.

By the way your source was incorrect about the STG44 round verses the 7.62x39. The STG44 bullet was 7.92, and based off the standard Mauser case but also shortened dramatically. The case was almost a millimeter larger in diameter (.471" verses .441"), plus the AK design was nothing but copy of the STG44. The STG 44 is commonly known as the first assault rifle, but it's not! There are a few earlier examples out there. The M1 / M2 carbines and maybe the British Sten gun predate the STG and AK series by years.

gary
RLlockie
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Posted: Wednesday, March 15, 2017 - 07:38 AM GMT+7
I'm not sure that I'd call the Sten (9mm pistol round) an assault rifle. Come to that, wasn't to .30 round used in the M1/M2 carbine also a pistol round? Assault rifles tend to use cut down rifle rounds, which the Sten certainly didn't.
Scarred
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Posted: Wednesday, March 15, 2017 - 09:25 AM GMT+7
The .30 Carbine 7.6233, was only used by the military in the M1 family of rifles. There are pistols chambered for it but those were developed of the civilian market.
trickymissfit
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Posted: Wednesday, March 15, 2017 - 07:03 PM GMT+7
in and artillery piece shooting a common steel casting, the round doesn't imbed into the rifling. The brass (usually brass) driving band does this job, and thus spins the projectile to stabilize it in flight. Yet with only one band the round would literally wobble going thru the bore, so there is an added area (or band) just ahead of the ogive. The diameter is machined very close to the minor diameter of the bore, but does not imbed into the rifling. The next issue between the two rounds is the rate of twist between the 7.62cm and the 75mm barrel. If (as one poster has stated) the German round was much longer, it would possess a higher ballistic co-efficient. Thus needing a higher rate of twist to insure stability. The shorter round would shoot OK with the higher rate of twist, but may develop an over stability issue (roughly 3/32" for every 100 meters). This becomes critical for long range shooting.

My guess would be that they redesigned the base of the projectile to fit the 75mm I.D. of the PAK 40 case. Similar to a U.S. 105 mm round. Reason why? The cases are made on an extruder, and then finished out in a die. Just going from 75mm to 76mm would have required a major tooling change. I also suspect that the projectiles were similar to the OEM Russian ammo, but with the bigger PAK 40 case. Just remember the that just because the round may be spinning faster, it doesn't mean it will stabilize in flight. It's all in the rate of twist.

gay
KurtLaughlin
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Posted: Wednesday, March 15, 2017 - 10:03 PM GMT+7

Quoted Text

If (as one poster has stated) the German round was much longer, it would possess a higher ballistic co-efficient.



The round, i.e. the cartridge, was longer. The projectiles were similar.


Quoted Text

My guess would be that they redesigned the base of the projectile to fit the 75mm I.D. of the PAK 40 case . . . Reason why? The cases are made on an extruder, and then finished out in a die. Just going from 75mm to 76mm would have required a major tooling change.



The documentary evidence is that the Pak40 case simply had an expanded mouth. This is not a significant change.


Quoted Text

I also suspect that the projectiles were similar to the OEM Russian ammo, but with the bigger PAK 40 case.



Yes, but that's because the Russian and German projectiles were very similar to begin with.

KL
KurtLaughlin
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Posted: Thursday, March 16, 2017 - 04:39 AM GMT+7

Quoted Text

The Germans measured the O.D. of the projectile differently (actually bore I.D.) than the Soviets. One measured from the diameter of the lands, while the other went by the diameter of the grooves . . . I seriously doubt there's much difference between the two bores.



Two statements here that need to be corrected:

> Both the Soviets and the Germans measured artillery in the same way.

> The 76.2mm Russian and 7.5cm German bores were different.

Both of these questions were resolved earlier and are apparent from manual illustrations referenced by Philipp. The bourrelet of a German 7.5cm projectile was 74.85mm in diameter and the projectile for the Russian gun was 76.1mm. The bourrelet diameter is a very close fit to the bore diameter of the tube, so the bourrelet diameter is effectively the same as the bore size.

KL