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View Full Version : Slash cut comp tumbles bullets?



kellysguy
12-09-2011, 08:05 PM
Hey everybody, new guy here. I have a M70 that was part of the first batch CAI had built a few years ago (new green mountain hammer forged barrel). Anyway, it would appear that this thing will throw bullets sideways. It'll put holes through 5/16" plate @ 100yds like you drilled it, then it'll throw a few sideways and won't even leave a dent. You can see where the round splattered sideways. It keyholes paper too. The gun doesn't have many rounds through it. I'm using wolf FMJ's and it passes the bullet test.

The only thing I can think of is the slash cut comp throws them sideways at that distance. I installed a regular comp but that made it shoot WAY low, so I went back to the slash cut.

Anyone have this problem before? I have two more unfired ones. I might give them a try.

Thanks.

imanaknut
12-09-2011, 08:53 PM
Welcome to the group !!! :welcome:

It is very possible the muzzle device is getting hit by the bullet as it leaves the barrel. I have seen an AK variant that had the threads on crooked, which is hard to believe, but it did cause the muzzle device to get in the way of the round.

If the rifle fires straight and true with the muzzle device removed, but gives problems with it on, I personally would just take the device off when shooting the rifle, and reinstall it as a thread protector for storage.

If the rifle still gives you problems with the muzzle device removed, I would have the crown checked to make sure it is square and true.

Another possibility is that the bullet nose is getting deformed as it is pushed out of the magazine and into the chamber. If it wasn't doing it all the time, there could be issues on the feed end of the barrel.

NATIONALIST
12-10-2011, 10:02 PM
i havea CAI yugo M70 B1 that does the same thing, i figured out the problem was boat tail bullets. if i shoot flat base bullets it shoots perfectly but if i use bt it will keyhole every time. try none bt bullets and see if that helps.

Schuetzenman
12-11-2011, 03:01 AM
i havea CAI yugo M70 B1 that does the same thing, i figured out the problem was boat tail bullets. if i shoot flat base bullets it shoots perfectly but if i use bt it will keyhole every time. try none bt bullets and see if that helps.

That would indicate the twist isn't sufficient to stabilize the longer BT bullet.

Highpower
12-11-2011, 10:18 AM
The only rifles I have had that keyholed had completely shot out barrels. If it only does it occasionally I would check and see if the brake is on tight as was mentioned. Also can you see any evidence of the bullet striking the side of the brake? If you could borrow a die guide and 14X1 LH die you could try and see if the threads are straight.

Other than that I got nothing. My Yugo with a slant brake shoots Wolf ammo to point of aim so I don't think the brake itself is the problem.

kellysguy
12-12-2011, 09:59 PM
Doesn't hit the comp. Well, it appears I have some barrel wear. I did the bullet test tonight and I'm really surprised by the amount of wear. I've put maybe 1K max through this gun (steel wolf) and it drop pretty far in there compared to the "new" guns and my Norinco. I assumed it passed the test before because of "low" round count. I'f say it's about half maybe a little more than the other guns. it seems (maybe) it throws more sideways the hotter it gets.

You guys got a pic of your barrel wear w/ aproximate round count?

imanaknut
12-12-2011, 10:15 PM
Green Mountain usually makes some good barrels. I can't imagine having that much wear after only 1000 rounds. I have a Romanian SAR-1 with over 13,000 rounds through it (ammo was much cheaper 10 years ago!) and the barrel still is like new.

Check the muzzle and crown very carefully. See if you can find a land with some material missing or a divot in the muzzle.

When you pull a patch through the barrel, are there any areas that seem to pull easier than the rest of the barrel or is it a smooth pull from breach to muzzle?

Highpower
12-13-2011, 07:13 AM
Barrel wear from shooting starts at the chamber end of a barrel. The hot gasses tend to erode the bore just ahead of the chamber and will progress towards the muzzle. It takes many thousands of round through a barrel to notice any significant degradation of accuracy.

What you will need to do at this point is to slug the barrel and determine just exactly what your bore diameter is. There is a possibility that you got a barrel with a slightly oversize bore. If the bore measures within specs, then you may have some muzzle/crown wear or damage.

Wear at the muzzle is almost always caused by improper cleaning. On firearms that are cleaned from the muzzle, the action of the cleaning rod wearing against the crown will screw up the accuracy of the barrel in short order. The crown is what determines what direction the bullet heads as it leaves the barrel.

If you look at the buttstock cleaning kit that comes with an AK, the cap is used as a muzzle protector. Apparently they thought it was important enough to give every solider the ability to protect the muzzle when cleaning. Whether it was used in the field is another matter

I have one other thought, severe copper fouling will also cause a barrel to shoot badly. Normally it takes a couple of thousand rounds to build up enough to affect the way your gun will shoot, but a rough bore would cause it to happen much faster.

NATIONALIST
12-14-2011, 04:04 PM
the GM barrel & crown on my CAI yugo M70B1 is perfect so it must be the rifling like schuetzenman said.

kellysguy
12-14-2011, 08:52 PM
.The crown is what determines what direction the bullet heads as it leaves the barrel.

.

One thing that has always puzzled me is, if the crown is so important, then how is a bullet supposedly able to fly straight after comming out of a slash cut comp?

The comp is, after all, an extension of the muzzle, right?

Could someone explain thias to me?

I still haven't had a chance to slug or test fire w/o the comp on yet.

Thanks for all the imput guys.

Highpower
12-15-2011, 05:25 AM
One thing that has always puzzled me is, if the crown is so important, then how is a bullet supposedly able to fly straight after comming out of a slash cut comp?

The comp is, after all, an extension of the muzzle, right?

Could someone explain thias to me?

I still haven't had a chance to slug or test fire w/o the comp on yet.

Thanks for all the imput guys.

Well it's an AK so straight is a relative term..............

I think that because the bullet is not constrained by the barrel at the time that it passes the slant brake it has little or no effect on the direction it flies. One way to make sure that the brake is not having an effect on the accuracy of your rifle is to simply remove the brake and see how it shoots.

My Zastava seems to have no practical difference in accuracy whether the brake is on or off.

kellysguy
12-19-2011, 12:52 AM
Last time I took it off it shot WAY low, like two feet @100yds. I was supposed to go shoot today but got jammed up. Hopefully I can tomorrow.

Infidel
01-05-2012, 10:53 PM
Hi Kelly, I may be off here, but if the other guys are telling you that it could be your compensator, I think they are right. Try taking it off again. That 2 feet low at 100 yds. may be the right place for your rifle to shoot. Re-adjust your sights with the comp. off. Check your target then. If that bullet just barely grazes that comp. then it will tumble and also be deflected up, hence the drop when it is removed. Start with a large piece of cardboard and check to see if you are still getting keyholing.
I still am trying to figure out WHY the slash compensators are on at an angle, as in having the bottom of the comp. at 7:00 instead of 6:00. ????

Highpower
01-08-2012, 10:51 AM
Hi Kelly, I may be off here, but if the other guys are telling you that it could be your compensator, I think they are right. Try taking it off again. That 2 feet low at 100 yds. may be the right place for your rifle to shoot. Re-adjust your sights with the comp. off. Check your target then. If that bullet just barely grazes that comp. then it will tumble and also be deflected up, hence the drop when it is removed. Start with a large piece of cardboard and check to see if you are still getting keyholing.
I still am trying to figure out WHY the slash compensators are on at an angle, as in having the bottom of the comp. at 7:00 instead of 6:00. ????

The angle slash cut on the muzzle brake is to compensate for the torque that the bullet exerts as it travels in a spiral due to the rifling. It is really only effective in full auto fire.

Infidel
01-09-2012, 08:02 PM
Thanks Highpower, I just happened to pick up a book on AK-47's today and read that the rifle rises and twists to the right, during full auto fire. I thought "Hmm, that's why!" Then I sat down this evening and you provided the same info. That's confirmation!
I happened to be at a gunshow a few weeks back and noticed that the compensators were on cockeyed. The first one was a Romanian and was crude enough I thought it must be one of the ones everybody warns you not to buy. I chocked it up to shoddy workmanship until I picked up another one at a different table and it was the same way. My Zastava doesn't have a compensator on it, so I didn't have anything to compare it to. :anim_beer-1: