[Trent]

I have an 8mm rifle; a semiautomatic Yugoslavian M76 rifle, which is horrible on cartridge cases. The ejected rounds impact the front edge of the dust cover, denting the case mouth, neck and shoulder of the cartridge casings. I've tried padding the front of the dust cover, it helps (a little) but doesn't completely solve the problem.

http://i.imgur.com/CGEa5.jpg

http://i.imgur.com/qVBbk.jpg

The case mouth is easy enough to fix with a pair of needle nose pliers (just insert while spinning, rounds out the mouth again).

The neck damage is then repaired when sizing. The bulge towards the back of the case is smoothed out by the small base die.

But the shoulder remains dented.

I know the shoulder will pop back out again when fired, but the volume of the case will be slightly reduced prior to this happening.

Should I continue with my current load or back off a little? I figure the brass is soft enough it SHOULD expand back out again quickly and avoid a pressure spike, but figured I'd check first.

[rsrocket1]

Yes the volume is reduced, but it isn't against a "hard" surface. Just like an uninflated balloon has less volume. 40-50,000 psi will not be impinged by the slight shoulder dent. Just keep an eye on those dents to ensure they aren't turning into cracks.

[Trent]

That's what I was thinking, too, but wanted a second opinion before I put my face that close. The Klashnikov action is pretty damn rugged, but still. :)

The MG34 and MG42 fired casings are MUCH worse than these, they actually fold the lip of the casing over. MOST of those I can straighten out I'm careful. The first time I tried "correcting" those I was getting about a 5% toss rate. Now I'm better, and don't have to throw any out.

I don't expect I'll get much more than 3 loadings out of these. Over 50% of the cases fail on the drop through 8mm case length gauge I have, and need to be trimmed after ONE firing, which tells me headspace is on the loose side. The bulge at the base of the case doesn't photograph well, but it's quite noticeable by Mk 1 eyeball and touch. That'll be the failure area; not a good place to fail, either. I'll have to keep a close eye on it.

[FROGO207]

Those dents are minor to me also. That thing eats brass for sure though.:eek: Let us know how the case life is when you get it figured out. Might help someone else someday.:) It would keep me from owning one as I want to reload with minimal fuss and that is a bother IMHO.

[Trent]

Frog;

It made me cringe when I started picking them up. There was one dent from the rifle, one dent from the wall (was shooting indoors out a window).

This fall when I shot reloads out the MG34 and MG42 I almost wept when I saw the condition of my precious brass after being run through those. :)

Still, with good 8mm surplus being GONE, and new ammo costing close to a buck a shot, I'll deal with the heartache.

Also, look at it this way: at least I don't have to spend all that time meticulously washing the rifles down after running corrosive junk through them. I *can* leave them sit in the bag overnight without pulling out a rusty gun the next morning. While not a big deal for WWI/WWII surplus bolt guns, washing a belt fed rifle down after shooting corrosive ammo is a major undertaking!

This Yugo M76 is a lot of fun to shoot. Unfortunately I don't have any bullets with cannelures in 8mm so I have to single-load the rounds, instead of feeding them from the 20 round magazine. It's unfortunate; even with the tightest neck diameter I can get AND crimping the HPBT bullets, the aggressive chambering never fails to seat the bullets back. In working up the load I found that it would set bullets back in to the case as far as .350"!!!

That's a serious issue. I didn't even notice it until I started shooting them and found that I was getting serious high pressure signs about 10% of the time. Flattened primers, cratered firing pin marks, bulged cases. Once I started single-feeding them the high pressure signs completely disappeared. (That was also when I discovered the set back, through manually cycling the action.)

The ramp on the M76 rifle sometimes "catches" the tiny hollowpoint on the Sierra Matchkings I'm shooting, sometimes ripping half of the hollowpoint off and deeply setting the bullet back in the casing. If I was shooting FMJ it would probably still happen, maybe not as frequently.

I'm thinking that when CAI assembled the rifle they got the rear of the magazine catch about .002" or so too high, angling the rounds ever so slightly downward towards the bottom of the trunion. I'm going to attempt a repair of this by altering the front of the feed ramp (integral to the trunion) to "smooth" the chambering of rounds.

(I had to do the same thing on a Norinco NHM-91 once upon a time, so it would feed hollowpoints; those would jam the projectile of even those steel-case/laquer sealed Wolf ammo back in to the cartridge casing).

I shouldn't HAVE to crimp ammo when I'm already sizing the neck .0015 under the minimum, and shaving tiny flakes of copper off the inserted bullet. It takes about 15 stout "WHACKS" with the kinetic puller to dislodge the things as it is. But the forces of them getting hammered in to the feed ramp ... must be huge.

Anyway, just part of buying a torch-cut/imported/reassembled by the monkeys at Century firearm.

[Walkalong]

They are fine to reload. Use something tapered and round to open the case mouth enough for the expander to go through. Size them as usual.

You can use any old thing you find laying around, like this thing I found somewhere. Works like a charm.

http://www.thehighroad.org/attachment.php?attachmentid=177269&stc=1&d=1357497845

[Trent]

Hmm. I've got bigger problems than the dented shoulders.

1. ONE of the dents in the shoulders is happening as they are chambering from the shoulder bouncing off of the lower trunions (left side feed only). That's why I couldn't completely eliminate the denting with padding on the dust cover.

2. The lands are WAY the hell underspec on this rifle. The 200 gr. Sierra Matchking calls for a cartridge OAL of 3.115. At this length, it takes a whack of a rubber mallet to start the extraction of rounds from the chamber, as the bullet is wedged in the rifling so hard.

To avoid contact with the lands I have to load rounds down to 2.915, a full 0.200 shorter than spec. I have NO idea what this deep of seating depth would do to pressure, and won't go there.

Don't plan on finding out; there's no point, as anything shorter than 3.050 will NOT chamber properly. The cartridge is guided in to the chamber by the bullet contacting the lower trunions; it ends up jamming against the face of the barrel, and getting hammered in to the casing by the forward momentum of the bolt assembly. (The exception is the last round of the magazine, which is guided by the follower to the center of the chamber; it does not contact the trunion; but this only applies to the last round fired in the magazine.)

3. No matter WHAT length I load them the cartridges BARELY enter the chamber. The nose of the bullet "skips" off of the lower edge of the chamber. I do NOT want to remove material from the barrel to form a lip as I already see signs of brass bulging on fired casings; the headspacing is already on the loose side, so taking material off the chamber is not high on my list of stuff to do.

This rifle already has a history. When I bought it used at the pawn shop it would NOT cycle. I had to do some surgery to the gas block assembly as the piston was jamming in it. You couldn't even take off the gas tube / upper hand guard off the rifle without inserting a crow bar between the tube and the barrel! As I received it, you couldn't even properly chamber a round.

Century Arms Gorillas .. sigh.

BTW, this is serial #00002 - so it was the second M76 they ever built. I hope they got better as the serial run went on, because this rifle is a serious problem child.

[Trent]

Also worth noting. The "rough chambering" is sufficient to cause loss of concentricity when chambering; not only is the hollowpoint tip sheared and some metal removed by the lower portion of the barrel, but the casing is slightly BENT when it enters with full force.

10 shot group size at 300 yards averages 5.5" when loaded singly in to the chamber by hand. This size more than DOUBLES when I allow the action to feed rounds from the magazine.

Some pics to illustrate;

Left side feed at point of contact:

http://i.imgur.com/iqRTH.jpg

Right side feed at point of contact:

http://i.imgur.com/o1qma.jpg

Left side feed closeup of contact:

http://i.imgur.com/f8KJw.jpg

Dummy rounds loaded to 3.115" (after extraction with hammer):

http://i.imgur.com/vCjzZ.jpg

(Land markings measure .200" from front to back, WAY too short to allow chambering if I load them back that deep)

Bullet stuck on chamber face after-effects:

http://i.imgur.com/vKSdD.jpg

[homatok]

Quote "I don't expect I'll get much more than 3 loadings out of these. Over 50% of the cases fail on the drop through 8mm case length gauge I have, and need to be trimmed after ONE firing, which tells me headspace is on the loose side."

For some "headspace" problems, partial-full-length sizing is an answer that will extend case life!

[Trent]

Unfortunately if I don't run the sizing die down flush with the shell holder, those bulges at the rear prevent it from chambering fully. And they are a REAL pain to extract when they DO chamber.

By "in contact" I mean it nearly jams my press up. I'm thinking about turning a bit of the end of the die off just to get it a little more snug without having to put that much force on my press, not good for the mechanism on my turret press.

I'll give up a little case life to avoid malfunctions or a possible out of battery fire.