This is from a spare Colt 6920 M4 upper I had. I had the Barrel Turned down to 11.5" in the lathe and then Lathe threaded (is there any other way
) to standard 1/2x28 threads. The barrel was also recrowned using a 4 jaw chuck and feeler gauges for dead bore center. The proper size gas hole was then made (.069 drill size). Barrel, FSB, and flash hiders were refinished.
My partner and I ran this upper in semi and full auto with a few different bolts and it ran flawless using standard 55 gr ammo. We put about 250 rounds through it as I never fired it even before the conversion. We also did a bench accuracy test at 100 yards and were getting 10" groups (this was also after the barrel was warm.
This is a must have for those who want a less expensive Colt commando upper with M4 feedramps and 1:7 twist but 100% reliability. The upper has charging handle but no bolt or carrier. Also has colt A3 carry handle sight and white RAS markings on flat top. Upper is 99%, no marks or anything like that.
$500 Shipped or will consider reasonable offers. All NFA rules apply. I also have a 5.5" flash hider for those who want to perm attach to make a 16" barrel. I'll throw it in for free if you want it.
Pics below. Contact by e-mail. USPS MO or check only.