A gentleman by the name of Ned Christiansen makes a 5.56 chamber gage. If you insert the gage into a chamber (must be clean) and it falls free, then it is a 5.56. If it sticks or otherwise doesn't fall free then it is a .223 and needs to be reamed. He makes a true 5.56 reamer that does this.
Bushmaster, DPMS, Stag Arms, CMMG and a host of others are well known for having chambers that were too tight.
Every one of the 500 Bushmaster carbines we had in Iraq exhibited issues with the chambers and I had to hand ream each one with the reamer. Then I added the extractor upgrade and the malfunctions dropped to almost nil.
I even did side by side comparisons with a Colt 14.5" upper and an LMT 10.5" upper that I had in the armory. When I ran them side by side with the Bushies using the same ammo (M855, Prvi Partizan SS109 and Bulgarian SS109) they all functioned as they were supposed to. The non-reamed Bushies exhibited about a 40% failure rate (either a failure to extract or primers blowing out).
Currently in the U.S market there are only a few companies that make barrels (chrome lined) that are even close to being reliable. FN, Daniel Defense, Colt and Noveske round that list off.
Quote:
Originally Posted by Gene Econ
OK -- now I am curious.
What process did you use to inspect the chambers and how are you sure the chamber was the problem and not the gas system / timing?
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