I am planning a build a mk12 mod 0 clone but in 6 mm ARC. I Already have a proof barrel, however it’s rifle length +1. So my question is, do you think it’d be possible to use this barrel for a mod 0 clone? I know everythinf is pretty tight on the mod 0 so it may not work. However Id hate to not use this barrel since it was free. Below is the barrel I have which I have as well as mk12 specs 
- Thread starter G3A3A1
- Start date
Problems: The standard PRI MK 12 Mod 0 forend will be too short for the +1" gas system. The PRI flip up front sight won't work with the short Proof gas block journal. There's no shoulder on the Proof barrel for the Ops-Inc barrel collar. I don't know if you can get an Ops-Inc style muzzle device threaded 5/8-24 for the Proof barrel or not.
The idea of a modern 18" 6mmARC SPR is however very sound.
The idea of a modern 18" 6mmARC SPR is however very sound.
What about seeing if Ron will do a custom extension similar to the M4 Extension Adapter?
Allen Industries
Allen Industries
I think you are trying too hard to put a round peg into a square hole. You did not mention running suppressed, but that is an entirely different set of issues.
I like the idea of a 6 ARC on a Mk 12, for sure. As a builder of Mk12 riles, I would personally see that as a possibility, but given the other projects on our plate, maybe a 2024 offering. But the barrel needs to be profiled correctly. As @MSTN mentions, you have gas journal issues, gas tube length, lack of a shoulder for the collar. Perhaps gas port size if running suppressed....
If I were you, I would put that barrel to good use and get a good receiver set host and MLOK rails. The potential of 6 ARC is there, but not everything can be 6 ARC overnight. There are some other practical issues that are causing some builders to look at dedicated 6 ACR receivers and BCGs. I am no expert on 6 ARC, just learning, but it is not as simple as a move from .308 to 6.5 CM.
I like the idea of a 6 ARC on a Mk 12, for sure. As a builder of Mk12 riles, I would personally see that as a possibility, but given the other projects on our plate, maybe a 2024 offering. But the barrel needs to be profiled correctly. As @MSTN mentions, you have gas journal issues, gas tube length, lack of a shoulder for the collar. Perhaps gas port size if running suppressed....
If I were you, I would put that barrel to good use and get a good receiver set host and MLOK rails. The potential of 6 ARC is there, but not everything can be 6 ARC overnight. There are some other practical issues that are causing some builders to look at dedicated 6 ACR receivers and BCGs. I am no expert on 6 ARC, just learning, but it is not as simple as a move from .308 to 6.5 CM.
What is the benefit of dedicated 6 ARC receivers and BCGs?
Maybe sell the barrel and get one that meets the specs you are looking to build?
Become a supporter and sell it in the marketplace.
Path of least resistance.
Become a supporter and sell it in the marketplace.
Path of least resistance.
This is what I will do. my friend gave me the barrel so I wanted to use it butni may have to buy one with a rifle length. Although I’m a little worried about 6mm arc reliability. As others has said it doesn’t seem as simple as 308/6.5 or 556/300
Not exactly the SPR handguard setup but I have a mk12 ish rifle, but I ran a 15” PRI on my 6mm ARC. Rainier Arms barrel 18” with a Rifle+1.
Not the traditional one with the cool front sight, but scratches the itch for me.
Not the traditional one with the cool front sight, but scratches the itch for me.
The camo pait job on this is
. You deserve to be told if you haven’t
With the longer rail, it reminds me of an extended Mod H. Love it
Who makes that Arca rail?
MK 12 Mod H in 6 ARC - 16" Proof. .5MOA groups with factory 108 ELDM and will ring steel all day at 1,000 YD... transonic around 1,050 YD. Yes the gas block sticks out of the hand-guard and you can't run the nostalgic OPS INC clone cans, but the increased performance more than makes up for it.
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