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9/22/2017 12:11:25 AM
Posted: 9/5/2005 10:16:48 PM EDT
My 14.5 inch Colt M4 keyholes at 7 yards about once in every 20 rounds. Accuracy is actually pretty good: about 2 inches at 100 yards. Sometimes I actually get two holes for one "bang" at 7 yards! This is not a "double" either - just one "bang." I wonder if the jacket is coming off. I have tried the same ammo in other rifles and it's fine. I have used other ammo and it does the dame thing. I primarily use 62-grain AE for practice. The barrel has 13K through it, but three armorers from three agencies have all told me that the barrel is fine. The twist is 1/7. I am at my wit's end. One armorer told me that M4's just keyhole sometimes, but I know that my teammates's carbines don't tumble rounds like mine does. This occurs even after cleaning an lubing. Any suggestions? What is the matter with this thing?
Link Posted: 9/5/2005 10:46:42 PM EDT
[Last Edit: 9/5/2005 10:47:32 PM EDT by Dano523]
If your getting 2 moa, then let it tumble.
Hell, think of it as pre-yawing before it even gets to the hard target.

Really, sounds like the jacket is coming apart if in fact the rifle will print 2 MOA. Might even be slivering the jacket on the gas port.

P.S. if the barrel is chrome lined, at 13K rounds, the barrel is just breaking in.
Link Posted: 9/6/2005 5:45:59 AM EDT
Are you absolutely sure the twist in 1 in 7 inches? Keyholing is usually a symptom of bullet instability and twist rate not being appropriate for projectile stabilzation. Don't believe what others say, verify the twist rate for your self. Also think about trying other bullet weights such as 68, 69, 75 and 77 grain ammo.
Link Posted: 9/6/2005 8:33:51 AM EDT

Keyholes at 7 yards but not at 100?

Could be over stabilized causing jacket to seperate. Bullet may yaw shortly after leaving barrel if its over stabilized but correct itself down range. Going to a heavier bullet should fix that.

Shok
Link Posted: 9/6/2005 6:52:44 PM EDT
Thanks, fellas.
The barrel is stamped 1/7 right on it. It's good to hear that 13k rounds is just breaking in a chrome-lined bbl. I have heard the theory about the bullets stabilizing downrange; I guess I believe it, but that's just bizzare. The bad news is this is a CQB weapon and what it does at 7 yards is more important that at 100 yards.

I have to stick with 62-grain bullets, but they should do fine in a 1:7 twist. I have seen 55-grain JSP pills come apart in a 1:7, but not 62 or heavier.

Maybe there IS a burr on the gas port, but more tham one armorer has missed it. That sounds like a very plausable theory. It goes back to the armory again next week. I'll see what they say.

Thanks for the help.
JR1
Link Posted: 9/6/2005 9:23:44 PM EDT
Are you having problems with the service ammo, or just your pratice ammo?
Link Posted: 9/8/2005 2:21:34 PM EDT
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