7.63 Mauser Issue

[Gazz]

Anticipating the test firing last year of a project gun, an 1896 Bolo Mauser, I bought 500 rounds of new made PPU 7.63 Mauser. It took until today to get it to the point where it was ready to shoot and after 3 rounds of the stuff I'm going to have to stop. The primers, while not backing out at all, are quite cratered with the crater part ballooned out as well. High pressure it seems. I had one stripper full of older US made ammo, Western and Rem Umc. Shot one of those and the primer looked like it should. This pistol has a new reline including chamber which was made from a piece of stainless 30-06 rifle barrel. Ejection is vigorous enough. I am going to contact the seller if I can remember who I bought it from. Then again maybe not and just shoot it in the Tokarev. Anybody ever hear of high pressure ammo from this maker before?

[DaveM]

I have shot thousands of rounds from PPU, including close to 1K of .30 Mauser. I've never had an issue, but of course every manufacturer sometimes puts out defective rounds.

[Dan Cash]

Sounds like your firing pin hole in the bolt is a bit large or the firing pin is a bit small.

[Larry Gibson]

Those may have been loaded to 7.62x25 pressures instead of 7.63 Mauser pressures. While the cartridges are considered "interchangeable" there is a distinct difference in operating pressures between the two.

[Der Gebirgsjager]

Interchangeable depends on which way. You can used the 7.62mm Mauser in pistols chambered for the 7.65mm Tokarev, but the other way around is inadvisable. Use of 7.65mm in a Broomhandle can very shortly lead to broken internal parts. I own three Broomhandles. One is inoperative due to broken internals, and locating parts is so difficult that I've never repaired it. How it got that way is known only to the Chinese from whence it came. Could be though that using 7.65mm in it is exactly what happened as the Chinese had gone to that round as standard before the pistols were imported to the U.S. While made of the best steel of the times, the steel used in Broomhandles is inferior to today's steel, and the pistols are quite old, and mostly quite used, which apparently yours was.

The barrel reline sounds quite good, but the remainder of the pistol is probably 100+ years old. Dan Cash's advice to check the firing pin hole and firing pin dimensions is a good place to start, and replacing all of the springs is a good idea.

As for the ammo, PPU has a fairly good reputation, but even if it is 7.62mm it may have been loaded hot. Your test firing of one U.S. loaded round is too small a sampling to draw positive conclusions, but it is worth following up on with further testing.
In the event that you conclude that the PPU ammo is too hot and the pistol is not the problem (both pistol and ammo may be part of the problem) then you can always pull the bullets, dump the powder, and reload them using an acceptable load and the same bullets.



DG

[nhithaca]

No idea of how hot Fiocchi loads their 7.62 but they do make it and it is available currently at a local gun shop here in NH.

[Larry Gibson]

Interchangeable depends on which way. You can used the 7.62mm Mauser in pistols chambered for the 7.65mm Tokarev, but the other way around is inadvisable. Use of 7.65mm in a Broomhandle can very shortly lead to broken internal parts.


DG

Appreciate the further explanation. By "interchangeable" I was simply referring that either cartridge could be chambered most often in either pistol. As I and you noted it is the higher pressure level of the 7.62x25 cartridge [loaded for the T-33 Tokarev pistol and the PPSH sub machinegun] than the 30 Mauser loaded for the M96 pistol and the derivative copies of it.

[Outpost75]

The .30 Mauser has a bit longer case neck, which sometimes impinges against the origin of rifling in some 7.62x25 chambers. Starline has a warning on their web site. However wartime PPsH SMGs and Soviet TT pistols don't care. But .30 Mauser won't lock up in my Cz52 and some TT copies of other than Soviet origin may have issues.

[gwpercle]

The .30 Mauser has a bit longer case neck, which sometimes impinges against the origin of rifling in some 7.62x25 chambers. Starline has a warning on their web site. However wartime PPsH SMGs and Soviet TT pistols don't care. But .30 Mauser won't lock up in my Cz52 and some TT copies of other than Soviet origin may have issues.

Check the chamber's throat (leade) and make sure it is long (deep) enough .
If too short... like Outpost75 states , the case/boolit may impinge (jamb into) and when fired the pressure will be excessive .
The barrel may simply need a little throating ... if lucky !
Gary

[Gazz]

Thanks for all the comments! I would think the leade or throat would have been created by the reamer which I had rented from 4D. They show the Mauser and Tokarev will use the same reamer aside from the very slight differences in the cartridges. I'll attach a picture of the fired cases to show what is happening - the top three were fired in my Romanian Tokarev, the middle three in the Mauser Bolo and the single also in the Mauser. If it is the the throat, why do the US made cartridges fire without the cratered primers? I only have 8 of those left, both Western and Rem UMC and really do not want to shoot them as I'm guessing they are collectable in their own right. The thought of pulling 500 bullets and then reloading to appropriate pressure is something I don't look forward to. I could shoot them in my Tokarev to "pull" the bullets, as the pistol seems to like them just fine but I really want to shoot the Mauser after the long rework process.

[Der Gebirgsjager]

Wow! Very educational! The first two, top row, are scary looking. Your Romanian Tokarev was meant for the higher pressure 7.65 mm cartridge, so primer strikes that deep using the slightly weaker 7.62 mm sure looks like high pressure to me. Third, top row, and all three in second row do have the look of excessive pressure. Bottom (Western) is still, to my experience, pretty deep, but the primer didn't flow.

I can understand your reluctance to shoot the old ammo, and it probably does have collector value. Apparently, based on your reply, you're not "that into" reloading? If the problem was mine I'd love the challenge to build the perfect load for my pistol via the process already described. Frankly, unless you can find a good supply of ammo that works well from another source, reloading would appear to be your only solution.

It's just always so difficult to diagnose firearms problems without having them in hand. Yours does not seem to be an issue of headspace. Like Larry Gibson indicated, the interchangeable factors are a bit complicated. The Eastern European world is awash in various pistols for the 7.65 mm such as the CZ-52, Tokarev, etc. and they do operate at high pressures. It may well be that PPU's idea of what a 7.62 mm should be is different from ours. The 7.62 mm was quite the item in its day, and was the pistol high velocity champion for years, but falls short of the 7.65 mm. Perhaps the problem lies not so much in the pressure as the metallic composition of the primers. The metal used in the primers may be softer, more ductile than the Western primer. Their color would certainly indicate the use of different materials.

Were the problem mine I would start by pulling a few bullets (you've already got 6 of them!), punching out the old primers, reloading with preferably CCI small pistol primers, using a load less than maximum from a reputable reloading manual, seating new bullets and trying again. The results may be pleasing.

DG

[Dan Cash]

We have not heard back from you on the condition of the bolt/firing pin hole. If the bore was gone to the point of needing a reline, corrosive gas leakage can assuredly opened up the firing pin hole in the bolt.

Another possibility is that the hammer is not supporting the firing pin well enough during firing which allows the primer to flow back a bit.

I think you are going to have to reload some once fired brass with U.S. primers and see what develops. There are a number of variables such as head space, soft primer, unsupported firing pin, enlarged firing pin hole and others that I can not think of off hand which can create your primer conditions. Hard to tell without pistol and ammo in hand.

[Gazz]

I enjoy reloading enough but the thought of disassembling "perfectly good new factory" ammo just seems wrong. I do not find any enjoyment there. The fp hole in the bolt may be worn, actually undoubtedly it is but I can't remember if when I retipped the fp, I sized it according to the hole in the bolt although it is limited in size by the fp spring which slides over it. I think I started this project in the mid 90's so I don't remember some details. But then why is the US made cartridge not showing the issue? So maybe soft primers in the PPU ammo? I do have two other Mausers, a 1930 commercial that is much to nice to shoot and risk damage from this ammo if it is a problem and a Chinese return 1930 commercial but its bore is so worn, there is only hints of rifling. I do not think that pistol would provide meaningful results if I shot this ammo in it.

[DaveM]

Wow! Very educational! The first two, top row, are scary looking. Your Romanian Tokarev was meant for the higher pressure 7.65 mm cartridge, so primer strikes that deep using the slightly weaker 7.62 mm sure looks like high pressure to me. Third, top row, and all three in second row do have the look of excessive pressure. Bottom (Western) is still, to my experience, pretty deep, but the primer didn't flow. ...

DG

Let's be extra careful when discussing these cartridges, please.

.30 Mauser is the American designation for 7.63x25 Mauser. It was derived from the 7.65x25 Borchardt.

The Tokarev round's designation is 7.62x25.

Generally speaking, in terms of power, the 7.65 Borchardt is least powerful, then the 7.63 Mauser, then the 7.62 Tok is most powerful but the difference between the latter two is not as much as sometimes claimed. From my own research and experience (see below) the most definitive thing you can say about whether 7.63 or 7.62 is loaded hotter is, "It depends."

On the Prvi Partisan website, their 7.63 Mauser ammo is listed as pushing an 85 grain bullet to 460 meters per second or 1509 FPS from a 150mm / 5.9" barrel.

They list 7.62 Tok ammo with an 85 grain bullet (either FMJ or JHP) at 510 - 525 m/s (1673 - 1722 FPS) from a 250mm / 9.8" barrel.

So, if 7.63 and 7.62 were fired from the same length barrel it's likely that velocity would be pretty close.

I used to have a circa 1916 Wartime Commercial C96 that had a totally worn out bore. It would not cycle with 1990s production PPU 7.63 Mauser ammo, but it would cycle with early 1960s Yugo surplus PPU 7.62x25, which was noticeably hotter.

Unfortunately, PPU does not list chamber pressure on their website.

[Outpost75]

FWIW, I have measured indent on copper of both my Soviet TT33 and Cz52. Driven protrusion in both pistols is 1mm, or 0.039", significantly greater than US milspec for the 9mm M9 of 0.028-0.032". Furthermore, indent on copper is 0.5mm, about 0.020", the same as normally expected for an M16A2 rifle or M4 carbine, being substantially greater than the 0.012" minimum of the 9mm M9 pistol.

In loading the 7.62x25 I DO NOT USE PISTOL PRIMERS! I use standard small rifle primers such as Remington 6-1/2 or WSR which are analogous to the WW2-era US .30 carbine primer. Using softer, thinner cup primers such as Remington 1-1/2, CCI 500 or Federal 100, I normally expect about 50% perforations at the striker point, as shown in the photos above.

W.H. B. Smith lists USSR Type P-Ball at 1378 fps from the 12cm barrel TT33 Tokarev pistol, based upon the Soviet Red Army specification of 420 +/- 10 m/s. The US Army Foreign Science and Technology Center, Small Caliber Ammunition guide lists USSR “P Ball” as 500 m/sec (1,640 ft/sec) from the 25cm (9.8”) barrel of the PPSh-41 and 550 m/sec (1,805 ft/sec) from the 30 cm (12”) barrel of the PPSh43. This agrees with modern tests of Vietnam-era surplus ammo.

Hatcher's Textbook of Pistols and Revolvers (1935) described the 7.63 Mauser as developing 1300 fps. This was based upon US commercial ammunition loaded to a maximum average pressure of 29,000 cup. WW1 and WW2 German military loads approached 1400 fps when fired from the Mauser M96 with 5.5-inch (14cm) barrel, according to contemporary military references.

While dimensionally similar, the Tokarev cartridge has a shorter neck, converting the CIP Bar pressures to psi the 7.62x25 operates at higher chamber pressure, than the CIP specifications for the 7.63 Mauser,

https://bobp.cip-bobp.org/uploads/td...l-en-page9.pdf

https://bobp.cip-bobp.org/uploads/td...-mauser-en.pdf

...About 36,250 vs. 30,600 psi. So, WW2-era and later Soviet-era "burp gun ammo" should not be fired in the M96 “Broomhandle” if you want the gun to last.

[charlie b]

Too bad you can't measure muzzle velocity to confirm if these are the heavier loading or not.

I don't attribute a lot to cratered primers. Flattened, yes, most of the time. I've had several guns that would show cratered primers at less than max pressures. Just too much variation in firing pin vs the hole in the breech. Changes in hardness of primers can easily change the results seen as well.

And, as stated previously, do not fire the 7.62x25 ammo in the Mauser, even if they do fit.

[Gazz]

Thanks for all the comments. I did dig out my nice 1930 Commercial and put a few rounds of the PPU through it. The fired primers looked fine. So back to my project pistol. I measured the fp tip at .086" and the hole in the bolt face .090" so .002" all around. Seems good to me but I don't really know. There is a slight radius into the fp hole from the bolt face, sort of funnel like. It's slight but it is there. I will bush the fp hole to remove the "funnel" and reduce the clearance some - I don't want the fp to stick in the bolt.