Bore Too Tight for Plated Bullets?

[GuitarmanNick]

The firearm in question is a Yugoslavian M-57 pistol in 7.62x25mm. It has been quite accurate with surplus and my hand loads until yesterday.

The hand loads have an X-treme 110 grain .30 carbine plated bullet. The same load with a FMJ has been very accurate in the past and is relatively light at ~1150 FPS.

As I was testing the latest hand loads, it appeared that the majority of the rounds were key-holing or tearing apart, and grouping was not good at all. The target was supported, but not completely. It did have some "round" holes, but most were jagged and shaped differently.

Since I had not previously slugged the barrel, I did so a few minutes ago and was a little perplexed at the measurements. I double checked them, and triple checked them.

The lands are .303" and the grooves are .313". Bullet diameter is .308".

Could the bore be too tight for the plated bullets and causing them to ripped apart or damaged? Am I crimping the round too much(I only use a light crimp but did not change it from the FMJ setting on my die)?

Any helpful input from the MDS collective would be appreciated.

 

[lazarus]

The firearm in question is a Yugoslavian M-57 pistol in 7.62x25mm. It has been quite accurate with surplus and my hand loads until yesterday.

The hand loads have an X-treme 110 grain .30 carbine plated bullet. The same load with a FMJ has been very accurate in the past and is relatively light at ~1150 FPS.

As I was testing the latest hand loads, it appeared that the majority of the rounds were key-holing or tearing apart, and grouping was not good at all. The target was supported, but not completely. It did have some "round" holes, but most were jagged and shaped differently.

Since I had not previously slugged the barrel, I did so a few minutes ago and was a little perplexed at the measurements. I double checked them, and triple checked them.

The lands are .303" and the grooves are .313". Bullet diameter is .308".

Could the bore be too tight for the plated bullets and causing them to ripped apart or damaged? Am I crimping the round too much(I only use a light crimp but did not change it from the FMJ setting on my die)?

Any helpful input from the MDS collective would be appreciated.

No. You want .312 or .313 diameter bullets. My M57 slugs as .312 on the grooves. You’ll get a lot of gas blow by running a .308 or .309 with .313 grooves.

It is possible the bullets aren’t properly stabilizing by having the lands bite in enough, though they should be. Excessive gas blow could be throwing it off. Or the paper was getting pieces of plywood or OSB splinters making the holes very not round.

Anything sideways going through? Or is it just that the holes aren’t very uniform?

My M57 is generally innacurate. Minute of torso at 15yds. Minute of car at 50. I’ve found a handful of loads that actually have decent accuracy, but whether it is surplus or new manufacture 7.62x25 or hand loads, most stuff has trouble all staying on a 16x16 target past 15yds. And it aint me. From a rest it is no better and I am more than capable of putting every round in to a 16x16” target at 50yds with most of my pistols if I am shooting carefully.

100gr RNFP FMJ .312” bullets seem to group acceptably and run well. About 1200fps with BE. I’d imagine I could crank that up to around 1350fps with CFE pistol, but I haven’t worked up a load yet.

 

[GuitarmanNick]

Anything sideways going through? Or is it just that the holes aren’t very uniform?

Looked like both, actually. First shot made a round hole. Second shot looked like it key-holed. About 10 rounds into my shooting, holes began looking jagged. Shot 50 rounds and the target was such a mess, my hits could not be counted(pretty certain that I hit it 50 times). Had a mixture with very few "round" holes, and mostly jagged ones.
If the group was so tight that a count was not possible, I would not be concerned. That was definitely not the case. Slightly larger than a pie plate @ 25' which I do not consider to be good at all.

 

[babalou]

No. You want .312 or .313 diameter bullets. My M57 slugs as .312 on the grooves. You’ll get a lot of gas blow by running a .308 or .309 with .313 grooves.

It is possible the bullets aren’t properly stabilizing by having the lands bite in enough, though they should be. Excessive gas blow could be throwing it off. Or the paper was getting pieces of plywood or OSB splinters making the holes very not round.

Anything sideways going through? Or is it just that the holes aren’t very uniform?

My M57 is generally innacurate. Minute of torso at 15yds. Minute of car at 50. I’ve found a handful of loads that actually have decent accuracy, but whether it is surplus or new manufacture 7.62x25 or hand loads, most stuff has trouble all staying on a 16x16 target past 15yds. And it aint me. From a rest it is no better and I am more than capable of putting every round in to a 16x16” target at 50yds with most of my pistols if I am shooting carefully.

100gr RNFP FMJ .312” bullets seem to group acceptably and run well. About 1200fps with BE. I’d imagine I could crank that up to around 1350fps with CFE pistol, but I haven’t worked up a load yet.

hahaha I love you minute references. This is an interesting thread. I do not reload but love to read and learn..

 

[John from MD]

The firearm in question is a Yugoslavian M-57 pistol in 7.62x25mm. It has been quite accurate with surplus and my hand loads until yesterday.

The hand loads have an X-treme 110 grain .30 carbine plated bullet. The same load with a FMJ has been very accurate in the past and is relatively light at ~1150 FPS.

As I was testing the latest hand loads, it appeared that the majority of the rounds were key-holing or tearing apart, and grouping was not good at all. The target was supported, but not completely. It did have some "round" holes, but most were jagged and shaped differently.

Since I had not previously slugged the barrel, I did so a few minutes ago and was a little perplexed at the measurements. I double checked them, and triple checked them.

The lands are .303" and the grooves are .313". Bullet diameter is .308".

Could the bore be too tight for the plated bullets and causing them to ripped apart or damaged? Am I crimping the round too much(I only use a light crimp but did not change it from the FMJ setting on my die)?

Any helpful input from the MDS collective would be appreciated.

When I owned Combloc pistols, I used .312 bullets for best accuracy. I had no problem shooting cast bullets and they gave great accuracy. There were no plated bullets at the time and no bullet manufacturer made . 312 100gn bullets. I used either Bullseye or WW231 powder loads.

 

[lazarus]

When I owned Combloc pistols, I used .312 bullets for best accuracy. I had no problem shooting cast bullets and they gave great accuracy. There were no plated bullets at the time and no bullet manufacturer made . 312 100gn bullets. I used either Bullseye or WW231 powder loads.

American reloading had a metric crap ton for cheap. I picked up a few thousand for 7.62x25 and 32acp shooting. For about 5 cents a bullet, heck yes.

At a guess, they are seconds or pulls for 30 super carry. Possible they may have been made for a 327 load.

 

[GuitarmanNick]

I concur that .308 is not optimal for accuracy, but until the other day, the pistol had been fairly accurate with both surplus and my hand loads. Holes in my targets had always been round, too. Groups are not as good as what I get with my other surplus pistols, but still better than my results on Sunday.
The bullets are very different between the batches. The FMJs have a slightly conical, exposed lead base while the plated are absolutely flat at the base. Not sure if the conical base may help in sealing the bullet to the grooves when fired, but surely the flat base on the plated bullets will not help against gas leakage.
Based on the measurements, these bullets should still be relatively stable even if some of the gas leaks past the projectile. They are the same diameter as the FMJs used in previous loads and are making good contact with the lands.
Last night I took a good look at the rest of the batch and I think they have too much crimp when compared to previous loads. There is quite a visible difference in the crimp.
In their defense, X-treme does caution that too much crimp can damage their plated bullets and affect accuracy.
I plan on loading another small batch after adjusting the die a bit to lighten the crimp.
At this point, I will be satisfied if the all of holes in the target are round and countable, even if the accuracy will never rival my 1911.

 

[lazarus]

I concur that .308 is not optimal for accuracy, but until the other day, the pistol had been fairly accurate with both surplus and my hand loads. Holes in my targets had always been round, too. Groups are not as good as what I get with my other surplus pistols, but still better than my results on Sunday.
The bullets are very different between the batches. The FMJs have a slightly conical, exposed lead base while the plated are absolutely flat at the base. Not sure if the conical base may help in sealing the bullet to the grooves when fired, but surely the flat base on the plated bullets will not help against gas leakage.
Based on the measurements, these bullets should still be relatively stable even if some of the gas leaks past the projectile. They are the same diameter as the FMJs used in previous loads and are making good contact with the lands.
Last night I took a good look at the rest of the batch and I think they have too much crimp when compared to previous loads. There is quite a visible difference in the crimp.
In their defense, X-treme does caution that too much crimp can damage their plated bullets and affect accuracy.
I plan on loading another small batch after adjusting the die a bit to lighten the crimp.
At this point, I will be satisfied if the all of holes in the target are round and countable, even if the accuracy will never rival my 1911.

It is possible they are over crimped. Are you using a Lee FCD?

One thought on the base, the FMJ gas pressures may cause the base to spread slightly, like you mentioned, cutting down on gas leakage, but also making a smoother exit from the bore. The flat base, especially if it is not a perfectly sharp flat base, with excessive gas blow by, as the bullet is leaving the bore, that excessive gas leakage, may be causing the bullets to experience some yaw if the gas pressure on the base is not even leaking by as it exits the bore, which I'd imagine could be exacerbated by excessive gas leakage.

Mostly not much of a clue here, just spit balling.

 

[John from MD]

I concur that .308 is not optimal for accuracy, but until the other day, the pistol had been fairly accurate with both surplus and my hand loads. Holes in my targets had always been round, too. Groups are not as good as what I get with my other surplus pistols, but still better than my results on Sunday.
The bullets are very different between the batches. The FMJs have a slightly conical, exposed lead base while the plated are absolutely flat at the base. Not sure if the conical base may help in sealing the bullet to the grooves when fired, but surely the flat base on the plated bullets will not help against gas leakage.
Based on the measurements, these bullets should still be relatively stable even if some of the gas leaks past the projectile. They are the same diameter as the FMJs used in previous loads and are making good contact with the lands.
Last night I took a good look at the rest of the batch and I think they have too much crimp when compared to previous loads. There is quite a visible difference in the crimp.
In their defense, X-treme does caution that too much crimp can damage their plated bullets and affect accuracy.
I plan on loading another small batch after adjusting the die a bit to lighten the crimp.
At this point, I will be satisfied if the all of holes in the target are round and countable, even if the accuracy will never rival my 1911.

Too much crimp is a bad thing but with that short neck on the 7.62x25, you need some for bullet pull. .312 will give you better bullet pull.

Do you lay out tarps to catch the brass? I swear my CZ52 used to send the brass out 20 feet or so.

 

[GuitarmanNick]

It is possible they are over crimped. Are you using a Lee FCD?

Yes, sir. Crimp ring is more visible on the plated loads, too.

Do you lay out tarps to catch the brass?

No, sir. Not enough room at the indoor range for that. I usually use a catcher on my strong hand. Gets most of the brass, but still gotta pick some off of the floor. This pistol sends brass about 10 feet or so.

 

[lazarus]

Yes, sir. Crimp ring is more visible on the plated loads, too.


No, sir. Not enough room at the indoor range for that. I usually use a catcher on my strong hand. Gets most of the brass, but still gotta pick some off of the floor. This pistol sends brass about 10 feet or so.

You are lucky. Mine tosses it about 30 feet to my 5 o’clock. I suspect it would leave a bruise if it caught you.