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AR15.COM
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10/30/2014 3:45:09 PM EDT
I just got a Battlecomp AKBC for my Arsenal SAM7. What is the best way to check that the barrel threading is concentric? I have heard of people using drill rods in the barrel to check the alignment.
10/30/2014 3:56:45 PM EDT
[#1]
Pretty much that.
10/30/2014 4:03:34 PM EDT
[#2]
Any idea what size rod would be correct?
10/30/2014 5:08:24 PM EDT
[#3]
I don't think the size of the rod matters, just how sure you are that it's sitting completely vertical to check for concentricity

11/2/2014 12:03:27 PM EDT
[#4]
there are subtle differences in diameter between manufacture.  

For .308, and for silencers,  I use both a drill size L (.2900) and an M (.2950).  From Graingers.  Couldn't find a 19/64 (.2969).
11/2/2014 1:40:49 PM EDT
[#5]
Straight 5/16 wooden dowel from Home Depot.
11/3/2014 12:24:09 PM EDT
[#6]
Thanks guys. I will give it a try tonight.
11/3/2014 7:10:21 PM EDT
[#7]
Install the attachment. Remove the bolt carrier, put a light in the receiver and look down the bore from the muzzle - all circles should be concentric. Muzzle brakes and flash hiders usually have significant clearance so it would have to be way off before it could influence bullet flight. I haven't heard of any AKs with original barrels having this problem. There were some AR15 barrels with the bore off-center a couple years ago, but it would have to be so bad you could see it to have any effect with a flash hider. The problem there didn't get anyone's attention until some silencers were mounted. They have tight tolerances, obviously, and there were cases of interference. If you have a USA-made barrel, it probably would be good to check, but using rods in the bore usually doesn't tell you much, if anything. I have used a wood dowel but they don't make one of the exact diameter for .30 cal. However, it did confirm that I had threaded this barrel (Mosin Nagant) a little skewed. All I had to do was enlarge the muzzle of the brake on one side and refinish it. You really couldn't tell anything by looking. The rifle zeroed fine but after getting slammed in the shoulder with 7.62X54 a few times I sold it. I found that 7.62X39 and 5.56 NATO are good enough for me. :)
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