AR15: How bad is my crown?

[turnerdye1]

So a few years ago I had some major issues with some keyholing out of my fairly new rifle. As some of you may remember there were quite a few suggestions of what was wrong. If you'd really like to go back and read the thread here it is.
https://www.indianagunowners.com/forums/long-guns/200059-ar15-major-keyholing-issues.html

Well I thought I fixed the problem by switching out the ammo. Here is the thread on that if you're interested.
https://www.indianagunowners.com/forums/long-guns/201515-ar15-major-keyholing-issues-fixed.html

Well this weekend I went out shooting to sight in a new red dot and who would have guessed it... I had keyholing again!! I was shooting 55gr reloads, 69gr match reloads, and American Eagle 55gr. All of them keyholed... It blew my mind. I have shot maybe 2000 rounds out of this gun in the past since I had the last keyholing issues. And now out of no where its starts again with quality ammo at 50 yards.

Since its not the ammo this time, I decided to check the crown and muzzle device. My A2 birdcage did not have any dings on it or any brass shavings like others have mentioned. Then I looked at the crown and I found this.... Would this cause 50 yard keyholing? It was about 3 out of 5 shots that keyholed.

I don't really know if that is bad or not so I scraped the carbon off anyways and this is what I found underneath.

So what do you guys think? Is that bad enough to cause the bad keyholing or is my barrel actually shot this time?

 

[T.Lex]

I'm sorry. As a total AR n00b, what am I looking at?

Is that a carbon buildup UNDER the flash hider? Like, where the end of the barrel meets the front of the FH? If so, how did the carbon get under there - or is that the problem?

Looking forward to learning from this thread.

 

[Mr. Habib]

I have personally seen instances of carbon buildup at the muzzle on AR's causing severe accuracy issues like you are describing. I would thoroughly and very carefully clean the muzzle, reattach the flash hider and try it again.

 

[sloughfoot]

If in doubt about your crown, a brass round head screw chucked up in a drill and some valve grinding compound will fix it.

What you want perfect is the last point of contact between the bullet and the lands.

 

[AllenM]

It sure doesn't look pretty, but whether or not it would cause keyholing is hard to say. What sloughfoot said would work and let you know for sure, or if you want it recrowned on a lathe let me know.

 

[indykid]

In that last picture, that ugly shiny stuff is still carbon build up. That last bit is not always easy to get rid of. I use a wire brush on a dremel to get through that stuff to the muzzle itself. Then I runs several patches through the barrel to make sure I get out any crud that dropped into it when running the wire brush.

 

[BGDave]

I see no evidence of lands or grooves in any of the pictures. Might give it a real good cleaning and take a look. (not a bore snake, sorry no fan)

Then take a look at this. Don't know about everyone else, I was astounded. Long read, scroll down to barrel wear.

http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/#reliable

 

[Leo]

I see no evidence of lands or grooves in any of the pictures. Might give it a real good cleaning and take a look. (not a bore snake, sorry no fan)

Then take a look at this. Don't know about everyone else, I was astounded. Long read, scroll down to barrel wear.

http://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/#reliable

That rifling does look pretty weak. Even a brand new barrel could be defective..

 

[silentvoice71]

Tbh I really don't see much of what I'd call rifling. Buy a new barrel man. This is causing to many problems to even bother with. Save yourself the B.S buy a decent 1/8 twist barrel and move on.

 

[1911ly]

?

How insightful!!

Op: It's hard to see any rifling. Can you get closer pics? And clean the crap out of it. Try a brass bore brush in a drill for a few seconds at the crown and see what it looks like.

 

[sloughfoot]

Please keep drills and bore brushes at least 10 feet away from your rifle. Nothing good can come of it.

It does bring a long forgotten memory back though. I had a chromed 1X7 Colt barrel that I fired thousands of rounds out of when accuracy suddenly went to pot.
Exploring this, I was slowly pushing a tight fitting patch back and forth through the barrel trying to feel rough spots.

I found a carbon ring just ahead of the leade. No amount of brushing would remove that hard carbon ring. The only way I got it out was with JB bore compound. And it was not easy. I never had keyholing, just big groups.

My recommendation is to scrub the bore with JB until it feels smooth from one end to the other. Can't hurt anyway. Not like a drill with a bore brush anyway....

 

[phylodog]

Please keep drills and bore brushes at least 10 feet away from your rifle. Nothing good can come of it.

It does bring a long forgotten memory back though. I had a chromed 1X7 Colt barrel that I fired thousands of rounds out of when accuracy suddenly went to pot.
Exploring this, I was slowly pushing a tight fitting patch back and forth through the barrel trying to feel rough spots.

I found a carbon ring just ahead of the leade. No amount of brushing would remove that hard carbon ring. The only way I got it out was with JB bore compound. And it was not easy. I never had keyholing, just big groups.

My recommendation is to scrub the bore with JB until it feels smooth from one end to the other. Can't hurt anyway. Not like a drill with a bore brush anyway....

Quoted for truth

 

[Bigtanker]

Something else that works great is on carbon is Seafoam.

 

[midget]

Keyholing is normally a sign of either wrong bore diameter, or wrong bullet diameter. If it is a newer barrel, call the manufacturer, the barrel is likely out of spec.

 

[Titanium_Frost]

Keyholing is normally a sign of either wrong bore diameter, or wrong bullet diameter. If it is a newer barrel, call the manufacturer, the barrel is likely out of spec.

Key holing is only a result of a projectile not spin stabilized by the rifling, there are many causes. If there were wrong diameters involved the rifle would not be functioning as described and would either not cycle, or blow up.

 

[Cameramonkey]

Key holing is only a result of a projectile not spin stabilized by the rifling, there are many causes. If there were wrong diameters involved the rifle would not be functioning as described and would either not cycle, or blow up.

Or too small projectile/too large a bore? Im no expert but I could envision a "loose" bullet rattling its way down the barrel like a rock dropped down a well casing as it bounces around on the way down.

 

[rvb]

wait. I thought the AR15/M16 was designed to shoot bullets that tumbled. better for shreading thine enemy to tiny bits and all that. sounds like it's working perfectly.

If that's not the case, it will bring into question every piece of knowledge I learned while hanging out at the gun shop.

-rvb

 

[chezuki]

If in doubt about your crown, a brass round head screw chucked up in a drill and some valve grinding compound will fix it.

Please keep drills and bore brushes at least 10 feet away from your rifle.

I'm getting mixed messages here...

 

[T.Lex]

It's a 10.1 foot long brass round head screw.

:thumbs:

 

[sloughfoot]

I'm getting mixed messages here...

Yep. Mixed messages for sure.

Drill and screw/valve grinding compound=good

Drill and bore brush=bad