New AR in 7.62x39 keyholing

L

Lennyjoe

New member
Just built an AR in 7.62x39 with a barrel purchased off of gunbroker. Actually purchased 2 barrels and a buddy built one too. The barrel is 16" with a 1-10 twist rate.

We took them out today and used Yugo brass cased 124 gr FMJ's and Wolf 124gr JHP ammo.

Both guns keyholed rounds as seen below:

IMG00092-20110226-1326.jpg


A closer up view:

IMG00095-20110226-1326.jpg


I don't see anything in the barrel that is blatently wrong. Any suggestions?
 
You've got something wrong. A 1:10 barrel should stabilize 124 grain bullets at any speed.

So, I"m wondering if you've got .311 barrels and .308 ammo?

I think that you should slug the barrels and measure them. See what you've really got.
 
Yea, the 1-10 should be fine for the 124 grain.

So, I"m wondering if you've got .311 barrels and .308 ammo?
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You lost me there. Using standard 7.62x39 Russian Wolf ammo. Dont have any way of measuring the bore.
 
It should not matter, I use 125 to 150 grain .308 bullets in a .311/.312 barrel with no problems. I have seen that with the wrong twist rate or guys that shoot lead bullets and do not clean their barrels. The lead clogs the rifling. I would guess the twist rate is wrong or the rifling not deep enough.
 
Using standard 7.62x39 Russian Wolf ammo. Dont have any way of measuring the bore.
Click to expand...

Some 7.62X39 bores are .311 groove diameter with a bore that's larger than .300. Most American .30 caliber barrels have a .308 groove diameter.

Some 7.62X39 ammo uses .311 bullets, some uses .308 bullets. If you're shooting a .308 bullet down a .311 bore, then the bullet doesn't fit the barrel I've seen russian bores with sizes as large as .314. If you've got a .314 bore, then even a .311 bullet might not stabilize in it.

So, you bought some barrels off Gunbroker. What size are they? Are they .311, .308, or some other diameter? The only way to know that is to drive a soft lead slug down the barrel and measure it.

There is a pretty good tutorial here. LINKY! If you don't have the tools for the job, then any gunsmith should be able to measure your bore easily and fairly inexpensively.

Once you know your barrel size, then you can match the ammo to it.
 
Wow, I had keyholing with a mismatched 9mm lead bullet I was working up, surprised to see this with FMJ. I'd definitely slug the barrel and find out the real diameter.
 
somethings got to be wrong with your barrel. Ive got a bushmaster 762x39 and it stablilizes everything and will shoot 1.5 inch at a 100 with old black box wolf ammo and under an inch with good handloads.
 
Go online and buy a little CERROSAFE. This little block you will find on this link is all you will ever need as you can re-use it over and over again. I simply cut a disposable squishy earplug in half (so it isn't quite so long) and push it down the muzzle THAT YOU HAVE LIGHTLY OILED about .75" Then pour in the CERROSAFE and let it cool for about 10 seconds. Then put a cleaning rod in from the opposite end and knock the casting out with a sharp whack to the cleaning rod. Then measure the casting. I do this on every milsurp or used barrel I buy.
 
keyholing

One,
You have been duped with the wrong barrel
two,
that can still kill someone at 600 yards, albeit you will not get accuracy to your expectations !!
I am just saying !!
 
It is common for people to take surplus barrel blanks, and turn them down for the AR. Is there any numbers, proofs, and names on the barrel? Is it chrome lined? Was the chamber extension on the barrel when you bought it? Who put it on if so? If the head space is out, the bullet my be jumping to far to get in the rifling causing a host of problems, up to and including keyholing. Slug it and also check headspacing. Also check to make sure it is 1-10 twist. You can do this with a cleaning rod.

Put a patch on a jag on your cleaning rod (a cleaning rod with a swivel handle, NOT a USGI type).

Mark top dead center on the rod.

Push rod down bore.

When the top dead center mark rotates back to the top, measure the distance the rod has advanced.
 
“The bitterness of poor quality Lingers long after The sweetness of low price is forgotten.” -John Ruskin
 
heck those r better groups than iv seen some 7.62X39 cal aks shoot

i say the bullet is smaller that the bore
 
What distance from the target? Do the barrels have flash hiders on them? If so, are the flash hiders installed straight and the correct diameter? Even incorrect diameter bullets won't show full profile keyholes with every shot, some will be oblongs or only slightly tilted.
 
shoot into something you can recover a bullet in. Examine the bullet see if there is even grooves on it. Its an easier place to start.

This is how I found out the barrel in my cobra patriot was unevenly rifled.
 
What do you want the gun for?

On a gun of this nature used for self defence, keyholing is an advantage as destabillised bullet will do more damage.
 
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