I am still waiting. Now I am going to try and call them.
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FAQ ID # 581
Last Update : 2008/10/28
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Question / Issue
Is the gas port hole, on the barrel underneath the block, drilled to mil-spec? If not, is it bigger or smaller? I have a 16" barrel straight from the dealer. No modifications at all. XM-15 E2S, .223 caliber, Flat-Top Upper
Answer / Solution
The 16" barrels have a Mil Spec .063" gas port.
Direct Link to This FAQ
http://www.bushmaster.com/faqs/?f=581
FAQ ID # 1886
Question / Issue
What are the sizes of the gas port in 16" HBar(pcwa2s16), in 20" BBL Target Model, and in M4? Thanks!!!
Answer / Solution
The 14.5" M4 barrels have a .067" gas port, # 51 drill bit.
The 16" barrels have a .063" gas port, # 52 drill bit.
The 20" barrels have a .093" gas port, # 42 drill bit.
Direct Link to This FAQ
http://www.bushmaster.com/faqs/?f=1886
Regardless of what they claim, their systems are generally overgassed on purpose and their saying it is "mil-spec" is specious and just not true. Just see the many posts by experienced folks on this site noting the tendency of BM to be deliberately overgassed. In particular, see Rob_S's thread on the AR Chart. Here: https://www.m4carbine.net/showthread.php?t=6642