What do you think?

Smokin Joe · 05-23-2005, 06:17

A friend of mine is an avid reloader and shooter. He's a retired AF EOD guy so he's the cerebral over analytical type.

Okay here's the problem:
Armalite AR-15 has approximately 10k rounds through it
Using an EOTECH sight
Distance is 65-80 yards
No wind
55 gr Nosler bullets
(I don't know the powder load but its consistant same with the cassings)
Barrel recently was shortened from 20 inches to 16 inches a bird cage M-4 style flash suppressor was added as well.
He shot approximately 450 rounds and approximately 5% of his rounds key holed the target. Meaning they smacked the target at a solid 90 degree angle. It didn't matter if he was at 65, 70, 75, or 80 yards they still hit at a 90 degree angle. The key holed rounds are still with in a 3 inch group of the normal rounds fired. Normal group is 1 inch or less.

So here's what we are thinking:
Either deformed bullets, but not detectable to the naked eye.
Or with the recently chopped barrel and new flash suppressor there is a scag or something that is shaving 5% of the rounds that are flying out of the barrel.

Think my guesses are on track or are we way off?
What do you guys think it might be?
And finally what should we do to determine what the problem is? (i.e. what or how to troubleshoot it).

Thanks for the help.

**The Reaper** · 05-23-2005, 07:50

What is the twist?

TR

Smokin Joe · 05-23-2005, 08:02

Quote:

Originally Posted by The Reaper

What is the twist?

TR

1 in 9

**Team Sergeant** · 05-23-2005, 08:03

Sounds like the barrel is in need of a proper burial, its useful life has come to an end.

Regarding TR’s question, a faster twist means a shorter life span. (Rapid fire will also shorten a barrel’s life.)

TS

**The Reaper** · 05-23-2005, 08:22

Sounds like a stabilization issue to me.

Faster twist may not stabilize lighter bullets properly, and 1x9" is on the edge for the 55s. You should not shoot the M-855/SS-109s in a 1x12" for that very reason, and the 1x7" is prone to doing just what you described with M-193 ammo. 5% does not sound terrible, for a blaster. If he wants to find out, switch to a 62-69 grain bullet and try it. Did it shoot the 55s before without any tumbling?

If you suspect a flaw in the bore, get a borescope and check it out.

TS is right, if it has been repeatedly shot to a color change, it could be burned out.

Also, if it is chrome lined, the lining may be shooting out.

Not sure that I would want to chop a 20" to 16" because of cycle and timing issues, but that would be a function issue, not a stabilization issue.

Best of luck.

TR

BMT (RIP) · 05-23-2005, 08:38

In priority

The gunsmith screwed up the end of the barrel when he chopped it -- severe damage to the crown or the end of the barrel was cut off center -- thus having one side longer than the other. This would also cause bullets to yaw and pitch wildly as gas will escape from one side of the barrel before it escapes from the other side when the bullet leaves the muzzle. Remove the flash suppressor and check the crown and check to see that the end of the barrel was cut square. You should be able to see that one using a magnifying glass.

The flash suppressor was poorly attached to the barrel. If so, you should see damage to one side of the inside of the flash suppressor where the bullets were hitting it as they were fired. If the gunsmith threaded the end of the barrel for the flash suppressor -- he may have threaded it in a manner that put the flash suppressor off center. If he used pins -- chances are the holes he drilled for the pins damaged the barrel.

The flash suppressor is loose or was made out of specs. Thus the bullet is hitting the side of the flash suppressor periodically.

Your buddy is using a 75 or heavier bullet in a barrel twisted one turn in twelve (55 grain and lighter bullets). Check the bullet weight even if he swears they are 55 grains or under.

Your buddy is using a powder that is way, way to slow in burn rate for the bullet he is firing.

Remove the flash suppressor and see if that solves the problem. If so -- flash suppressor issue. If not, the end of the barrel isn't square or the crown is severely damaged. Either can be fixed.

**Peregrino** · 05-23-2005, 08:41

With 10K rounds through the barrel, it's time to turn it into a tent stake (or a boat anchor - you get the point). Unless your friend used a hacksaw, the price of a new plinking barrel isn't much more than quality gunsmith services would be to shorten a standard barrel. Your initial report left out a lot of info about why and how the barrel was shortened, any item of which could be a significant factor. The most probable reason for the keyholes is a less than perfect muzzle crown (and 10K rounds of wear). BTW - 1/9 will stabilize 55 gr. bullets without a problem. FWIW - Peregrino

Smokin Joe · 05-23-2005, 08:47

Thank you Gentlemen.

Very much appericated.

Peregrino,

I'm not sure how the barrel was shortened....I'm pretty sure though that he had a good local gunsmith do it....but who knows. Not my rifle so he could have used a ban saw for all I know. I will get more specifics.

But everyone's consense seems to be that his barrel is done anyway.

I will advise him to do all the things BMT suggested just incase its a crown problem.

Thanks again everyone I appericate it.