I currently have a Colt 6933 upper that I'd like to convert into a MK12 Mod 1 clone. If I have the 11.5" barrel cut down to 10.3", will I have to have the gas port modified?
Printable View
I currently have a Colt 6933 upper that I'd like to convert into a MK12 Mod 1 clone. If I have the 11.5" barrel cut down to 10.3", will I have to have the gas port modified?
i don't know what size port they come in to begin with.. i'm guessing .062..... if so, i'd open it to .070-.075. if you have ADCO do the chop, they'll probably open it to .084ish (cant remember the exact size)- i personally think that's a bit too much, can be hard to balance them out with NATO ammo.
available drill sizes will help dictate.. i don't know how varied ADCO/any other smith's collection is.
According to my knowledge base the Mk18 upper has a gas port diameter of .070 inches. The BCM 11.5" barrels are around .076 if I recall correctly.
Send it to ADCO and they will make sure the gas port size is correct also.
:cool:
I agree. Correct gas port size is the smallest that runs reliably. I had a 10.5 that was having cycle problems once I took the "Pig" off. The gas port was opened to .078
On the other end, I just built a 7.5" using a Rainier Ultra Match barrel and the gas port measured .056. It runs great. My only guess as to how it gets by is the ratchet rifling.
sell the one upper and buy another one, or at least a different barrel...not that cutting it down "can't" be done, just there are easier and better ways.
Velcro