7.62x25 Tokarev pressure limits

[7.65browning]

Hi All,

I've been working on a suitable load for a semi-auto converted submachine gun (these are legal where I live in Europe). My previous loads were too weak to push the bolt fully to the rear. I understand that the minimum muzzle velocity for 7.62x25 to work out of an smg is around 1650 fps. In order to get that velocity, I need to load 7 grains of the powder I'm using, however this would bring me to a pressure of around 38k psi while maximum allowed chamber pressure is listed at around 36k psi. Is it safe to fire these rounds or should I just pull them and get a powder more suited to this caliber?

Thanks,
Tom

 

[Dudedog]

I have never dealt with something like this so just general advice.

I would go with the slowest burn speed powder you could get that has listed loads for that cartridge..
Work up to MAX charge with that and hope that gets you function.
Going over the listed MAX is something only you can decide to do and needs to be done carefully if at all.

How did you come up with the 38K pressure number?
Pressure is not linear.
Interpolation between data points is reasonable, extrapolation past known data points can get you in trouble. (JMWO)
Did you use Quickload to arrive at the 38K number?

Be safe, have fun.

 

[ArchAngelCD]

The pressure limits are 42,000 CUP.

 

[fxvr5]

The pressure limits are 42,000 CUP.

What is the source of this number?

 

[ArchAngelCD]

What is the source of this number?

I got that number from here.
https://www.bevfitchett.us/accurate-smokeless-powders-reloading/xmm-tokarev.html

When looking around later in for something else I came across this that might help you too.
http://www.shootingtimes.com/gunsmithing/converting-a-1911-to-7-62x25-tokarev/

In reality you could have found these numbers just as easily as I did.

 

[fxvr5]

I prefer CIP pressure recommendations for cartridges not supported by SAAMI, since they use industry standard methods. The first author you cite has an unknown pedigree and CUP is not used any more.

http://www.cip-bobp.org/homologation/uploads/tdcc/tab-iv/tabivcal-en-page9.pdf

 

[Havok7416]

OP, if you already have data of some sort that is telling you 36k is the limit, then that's the limit!

Furthermore muzzle velocity has little to do with cycling of a weapon. As an example, I have a load in .45 ACP that generates about 400 fps at the muzzle (less than half of normal) yet ALL my guns still cycle (including an SMG-style .45 rifle) and the bullet still goes where I aimed it. An SMG shooting the Tokarev will be a simple blowback action unless it's something fairly obscure. Those don't take a ton of force to cycle.

 

[ArchAngelCD]

I prefer CIP pressure recommendations for cartridges not supported by SAAMI, since they use industry standard methods. The first author you cite has an unknown pedigree and CUP is not used any more.

http://www.cip-bobp.org/homologation/uploads/tdcc/tab-iv/tabivcal-en-page9.pdf

CUP is older but not used any more? Half or more of the Hodgdon load data site references pressures in CUP.

As for the first author, just because you don't know her doesn't make her unknown.

 

[7.65browning]

I have never dealt with something like this so just general advice.

I would go with the slowest burn speed powder you could get that has listed loads for that cartridge..
Work up to MAX charge with that and hope that gets you function.
Going over the listed MAX is something only you can decide to do and needs to be done carefully if at all.

How did you come up with the 38K pressure number?
Pressure is not linear.
Interpolation between data points is reasonable, extrapolation past known data points can get you in trouble. (JMWO)
Did you use Quickload to arrive at the 38K number?

Be safe, have fun.

I arrived at 38k by taking the load pressure in the reloading manual and adding 12% which is what I'd need to increase the load by to get to the muzzle velocity I want. I know it's not very scientific. The powder I use is not available in the US, at least not under the same brand name. According to the manufacturer it is very similar to Accurate #2, the recommended max load is 6.3 grains for 7.62x25 Tokarev.

 

[243winxb]

Watch for pressure signs. https://www.thehighroad.org/index.php?media/albums/high-pressure-signs.148/


Loads http://www.makarov.com/tokloaddata.html

What bullet weight are you using? Powder? Data?

The 71 gr would seem to get the higher welocity. But velocity has little to do with working the action.

Will factory ammo work the action?

 

[243winxb]

My previous loads were too weak to push the bolt fully to the rear

Is there a recoil spring that can be changed to a lighter one or shortened? Our blowback firearms are adjusted/tuned with different weight springs.

 

[243winxb]

7.62x25mm Tokarev Ballistic Performance
Bullet weight & type Velocity Energy
5.5 g (85 gr), JHP 376 m/s 1,230 ft/s 390 J 290 ft-lb
5.8 g (90 gr), FMJ 409 m/s 1,340 ft/s 488 J 360 ft-lb
5.5 g (85 gr), FMJ
"Czech Load" 500 m/s 1,640 ft/s 688 J 512 ft-lb

The so-called "Czech Load" is suitable for use only in handguns specially designed for the higher pressure such as the ČZ-52.

Energy more important. https://m1-garand-rifle.com/cz52/7.62x25mm.php

Our 9mm machine guns used a hotter load then standard.

 

[7.65browning]

Watch for pressure signs. https://www.thehighroad.org/index.php?media/albums/high-pressure-signs.148/


Loads http://www.makarov.com/tokloaddata.html

What bullet weight are you using? Powder? Data?

The 71 gr would seem to get the higher welocity. But velocity has little to do with working the action.

Will factory ammo work the action?

I'm using 85gr FMJ bullets and Lovex D032 powder. Data is from the Lovex factory reloading manual. Factory S&B ammo is a hit or miss, sometimes it cycles, sometimes it doesn't.

 

[243winxb]

May be a gun problem. Dry guns dont function well. Try cleaning it, then lube it?

 

[Dudedog]

Lovex DO32 is a pretty fast burning powder. (AA#2?)
I would try something slower, D036 or one of the D037s
The D037s look like they will get you there.
Form 2013 Lovex Data
Link to site
https://shootersworldsc.com/
The CIP Data lists the Lovex powders US data is Shooters world.
Shooters World imports Lovex powders to the US an renames them

Upping the charge 12% from the MAX with D032 is sure to lead to far more than a 12% increase in pressure.
If you plotted pressure it would be a curve not a straight line.

 

[7.65browning]

I decided to pull the cartridges. I’m pretty sure an SMG would not be damaged by these loads but I’d rather stay on the side of caution.

Thank you all for the advice!

 

[Dudedog]

I said curve, I probably should have said exponential curve.

Better to be old and not bold and keep all the important bits you were born with IMO.
Please let us know if you try a slower burn speed powder and it solves your issue.
Hope you get it worked out.

 

[7.65browning]

Thanks, it’s about time for me to get some new powder anyway so I’ll pick up something slower and will post an update.

 

[Dudedog]

Guessing but if you could get it D037.1 might be best. About the same burn speed as AA#7 according the manual.
DO37.2 (about the same as AA#9) is probably a little to slow burn speed wise.
Various other powders as well but guessing since you are in Europe it might be easier to get D037.1
Here is some data for Vectan and Vihtavouri (which also might [or might not] be easier for you to get than say a Hodgdon or Alliant powder)
Maybe N340 or 3N37, 3N38 is pretty slow but they list it and it has the best vels.



Note: I don't load the round so just guessing on powder, so I may be completely wrong.

 

[7.65browning]

Update, I got my hands on some D037.1. Will load up some rounds and see how they perform.

 

[Carl N. Brown]

CUP is copper units of pressure measured literally by the crush of a copper cylinder by a piston through the cartridge and primer, which is more like the average PSI pressure pounds per square inch over time.
.
The more modern method is to measure pressure by an electronic transducer which more accurately captures peak pressure, maximum stress, but even there CIP, SAAMI and NATO measure pressure either at different points of the chamber or even at the barrel in front of the case mouth.

I have not seen a reliable conversion between CUP and transducer measures; they are consistent within the same method, but hard to compare across methods.

That chart shows large pistol primer for 7.62x25mm.
All the 7.63x25mm and 7,63 Mauser boxer primed casings I have seen and used have been small pistol primer.
I have found reloading for my old C96 Mauser that a load developed for minimum recoil for positive action with small pistol magnum primer or small rifle primer will not produce positive action with small pistol standard primer.

 

[Walkalong]

The powder I use is not available in the US, at least not under the same brand name. According to the manufacturer it is very similar to Accurate #2

Sounds a bit fast for the application, have anything slower?

 

[Walkalong]

Ah, I see Dudedog has you covered.

 

[Dudedog]

Hope D037.1 works out for you.

 

[7.65browning]

Hope D037.1 works out for you.

Thanks, and thank you for all the help also. I just finished loading up my test rounds and the powder had a really strong acetone smell, much stronger than other powders I used. Is that normal?