Bullets tumbling

[Topgeer]

I have an open gun that was built by couple different people.  It started life as a 38sc and is now a 9mm.  I'm having a problem with tumbling bullets... Lots of tumbling bullets like 30 plus every match.  The kkm barrel has 6,000 or less rounds through it.  I've had the rifling and crown checked. Gunsmith said they both look like they're in excellent shape. I thought maybe it was the comp even though it checked out okay as well. So I bought a brand new Binary Eng CFD Titanium Compensator 3 Port and had it installed and had an aliment ream done.  Same thing tumbling bullets.  Gun shoots flawless never had a problem with function.  Also runs flat and even when the bullets are tumbling they are doing so accurately.  I'm just at a loss here and don't know what to do other than trying to change out the barrel again.  Any info or things to try/check would be great.  

 

Also I have tried friends ammo though it and it does the same thing. 

[Sarge]

My money would still be on comp strikes

[Topgeer]

How its been aliment reamed?  Been checked multiple times and is new. 

[Sarge]

9 minutes ago, Topgeer said:

How its been aliment reamed?  Been checked multiple times and is new. 

What is the load? What was buddies load? If your load has not changed and just started tumbling out of the blue, and a buddies load tumbles in your gun and not his, it almost has to be a comp issue.

 Many open guns have been reamed, aligned etc and still suffered from comp strikes. They don’t really leave marks on the comp so it’s hard to tell.

[Topgeer]

We both shoot almost the same exact load he uses 8.3 I use 8.4 ws6 and 124gr PD hollow points.  

 

If it was still comp strikes what would be fix?  

[Sarge]

25 minutes ago, Topgeer said:

We both shoot almost the same exact load he uses 8.3 I use 8.4 ws6 and 124gr PD hollow points.  

 

If it was still comp strikes what would be fix?  

Reaming it out larger. Recently somebody on hear who builds guns said they team them oversized slightly for insurance agains strikes 

[Guy Neill]

If ruling out anything to do with the comp, bullet tumbling would relate to the bullet, the velocity and the twist.

 

What is your barrel twist and bullet velocity?  For a 124gr making a 170 power factor. a 1:10" twist will normally give almost 100,000 RPM.  A slower twist rate will, of course, give less RPM.  What RPM is needed for bullet stability would need to be determined.  Does your friends gun have the same twist rate as yours?

 

The most common cause of tumbling is low velocity (giving low RPM).  Causes of low velocity can be bullet diameter, barrel bore diameter or  load.

 

Assuming the ammunition shoots well in your friends gun, it suggests a problem with your barrel.  Larger bore diameter, less rifling or slower twist rate.

 

Thus, a number of things to investigate.

[zzt]

If you are getting comp strikes something else is wrong.  Either the comp reaming was not aligned properly, or there is a problem with the barrel.

 

If Binary's installation instructions were followed, and EGW alignment reamer was used.  So there should be no problem with alignment.  If the barrel was chucked in a lathe and reamed, it may be off.  You can check that by using the EGW reamer.

 

If the threads are not full and there is a little wobble of the comp on the threads, it may go on cocked.  Threads should be so full that some effort is required to screw on the comp and clock it.  Also, the heat of rapid firing may have loosened the Loctite and the comp wobble on the barrel.  That could cause strikes.

 

If both of the above check out ( I would doubt it ), it is the barrel.  Have the crown and end of the barrel inspected and measured.  You can't just look at it and say it looks okay.

Edited May 23, 2021 by zzt

[Lastcat]

4 hours ago, zzt said:

If the threads are not full and there is a little wobble of the comp on the threads, it may go on cocked.  Threads should be so full that some effort is required to screw on the comp and clock it.  Also, the heat of rapid firing may have loosened the Loctite and the comp wobble on the barrel.  That could cause strikes.

 

Yep, I was just about to mention this too. If your comp was installed and was loose on the barrel to begin with, then what is keeping it aligned is the Loctite. If you are practicing and firing enough rounds to get the comp hot, it is possible for the comp to loosen and settle after it cools down. If this is your case, I would check the alignment of the comp to the barrel bore again. 

[jim vaughan]

Bullet diameter mismatch?

Try larger bullets.

[Topgeer]

14 hours ago, zzt said:

If you are getting comp strikes something else is wrong.  Either the comp reaming was not aligned properly, or there is a problem with the barrel.

 

If Binary's installation instructions were followed, and EGW alignment reamer was used.  So there should be no problem with alignment.  If the barrel was chucked in a lathe and reamed, it may be off.  You can check that by using the EGW reamer.

 

If the threads are not full and there is a little wobble of the comp on the threads, it may go on cocked.  Threads should be so full that some effort is required to screw on the comp and clock it.  Also, the heat of rapid firing may have loosened the Loctite and the comp wobble on the barrel.  That could cause strikes.

 

If both of the above check out ( I would doubt it ), it is the barrel.  Have the crown and end of the barrel inspected and measured.  You can't just look at it and say it looks okay.

EGW reamer was used to install and all the Binary instructions were followed. I had crown and barrel check but I don't know how he did it so I will follow up on that.  I do notice that they don't start to tumble till after a few shots are fired.  So wondering if its the heating up causing it.  

[BadShot]

Could you take the comp off and fire some rounds thru it to see what happens?

[Absocold]

^This.

 

If no, try some factory rounds and see if they tumble.

 

When all else fails, I use a lathe to turn down a piece of balsa wood so it almost fits down the bore. Dust it with graphite powder (liquid lube will make it swell up) and tap tap tap from the breech end until it starts coming out through the comp, watch for shaving.

[Topgeer]

40 minutes ago, BadShot said:

Could you take the comp off and fire some rounds thru it to see what happens?

I was talking to buddy about doing this.  If I get little extra time this week I'll try that as well.  I'll run some factory ammo with comp then without it and see what happens.  

[MikeBurgess]

Running the EGW comp reamer in the comp is not a golden bullet depending on the comp in use (I have not used a Binary comp so no info on it) some comps are long enough that not enough pilot is in the barrel to align the reamer portion enough to get it centered, I had this issue on a longer comp I installed a few years ago. 

 

Now when I make a comp from scratch I ream it .375 for a little more safety factor, im not too worried about loosing 10 thousandths of a baffle, the area of the hole is only .005 sq inches larger and the bullet is only "plugging" it for about .00003 seconds.

[Paul B]

Seems you have checked most things but I had the same problem early on and it was caused in the reloading process. If you have too much crimp it can cause this as the bullet is effectively reduced in size. Also slug the barrel to see exactly what bullet you need to shoot. I have heard 9 mm liking .355, .356 and even some at .357.

 

In my case the crimp thing was the problem.

[Topgeer]

3 hours ago, Paul B said:

Seems you have checked most things but I had the same problem early on and it was caused in the reloading process. If you have too much crimp it can cause this as the bullet is effectively reduced in size. Also slug the barrel to see exactly what bullet you need to shoot. I have heard 9 mm liking .355, .356 and even some at .357.

 

In my case the crimp thing was the problem.

I was told this at the range also.  I have tried couple factory ammos as well as couple different friends loads.  Always tumble... Guess it could still could be this though.  I talk to my machine shop yesterday.  I'm gonna ream comp to .375 first.  Couple people on here recommend this so we measure my friend honcho and it was .375

 

[Sarge]

1 minute ago, Topgeer said:

I was told this at the range also.  I have tried couple factory ammos as well as couple different friends loads.  Always tumble... Guess it could still could be this though.  I talk to my machine shop yesterday.  I'm gonna ream comp to .375 first.  Couple people on here recommend this so we measure my friend honcho and it was .375

 

Yeah, I don’t as going to say crimp is ruled out since multiple loads tumble

[Steve RA]

I run .358 in my 9mm Kart NM barrel.  Groups very well, still not quite as well as my .45, but I'll get it there.

[Stevenchrist]

I will still prefer comp strikes .

[rpm8300]

In situations like this its almost always the comp - even if it is not actually touching the comp, an uneven path through the comp will cause this.  It may be worth sending to a gunsmith.

[konkapot]

Going to make a horrible hideous suggestion here. 

 

Why can't I use a rotary grinding tool on the comp. This tool (which has nothing in common with a dremel) would be adequate to make the hole in the comp bigger...hence solving the problem...?

 

Prepared to be wrong. 

[shred]

Hopefully OP isn't still putting up with it nearly 3 years later..

 

Reaming with a proper reamer will keep the comp holes concentric to the barrel.  A dremel, not so much. 

 

Concentricity can be important since a bunch of gas is trying to cram through the hole at the same time as the bullet and more on one side than another can push it off track.

 

 

 

 

[Topgeer]

It ended up being a bad barrel. It lts actually being changed now and will be my backup gun. I have a different gun that I shoot now.   

[konkapot]

Didn't want to start a new thread as my question was similar-ish.