The Relationship Of Barrel Extension Diameter To Accuracy In The AR-15, Part 2

Further quantifying the accuracy gains from the proper fitting of the barrel extension to the receiver, rebarreling and the new custom BAT Machine oversize extensions.

by Joe Carlos
photos by Gretchen Huffman

I built up dummy AR-15’s using a dozen barrels randomly selected from assorted custom barrel makers, all with standard barrel extensions. I machine rest tested them first with no shims or Loctite, firing three ten shot groups from each gun using different lots of ammo. Then I disassembled everything and reassembled the guns using shim stock and green #620 Loctite as discussed previously and tested them again using the same lots of ammo. Comparing the results the net gain was an astonishing 35% average reduction in group size!

If you recall, I had determined years prior that just using green Loctite as a stand-alone without the shim stock resulted in an 18.6% average reduction in group size. So, using simple math skills, I credit the addition of the shim stock to nearly doubling the results by adding about 16.4% of accuracy gain. Improving accuracy by 35% is well worth the 5 to 20 minutes of shop time and I am sure your customers would agree. If you have any doubt look at the test groups fired from two guns selected at random that appear in this article.


Read more in our April 2013 issue. Back issues are available.

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