Home CMMG 12.5" is the Bastard Sword of ARs

12.5" is the Bastard Sword of ARs

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Watch this video before you run out and build a half-baked 12.5″ AR.

12.5″ may be the sweet spot of length and velocity, but tuning the 12.5″ gas systems for running suppressed/unsuppressed is more difficult than it is with more well established barrel lengths. Is carbine or mid-length better? Not really.

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39 COMMENTS

  1. What is going on with people's lips lately. there is this new "trend" where they don't use one side of their mouths to speak. It's like everyone is having strokes and not talking about it.
    I see it everywhere and it freaks me out.

  2. Man, velocity was important in Iraq. I guess for plinking, SBRs are great……but if it was SHTF, I want 3-5x on my scope, and 18-20 on the barrel. Also, I don’t know what I’m talking about, just a GWOT grandpa nowadays…..I still haven’t come off the vertical grip usage. Lol

  3. The only length I havent played around with is a 14.5 pinned. I live 15 minutes from Green Mountain Barrel Co and they have 14.5 & 16" barrels for approx $125 so it would be silly to not give it a go. Ive got a 10.5 and 11.5 , I like knowing Im getting that extra out of the 11.5.

  4. if i build a 12.5 with a SME that is 4" is it SBR or is it a full length AR now? i wanted to build a 10.5 AAC but after the ATF issue i have decided not to do that on the grounds i like my gun rights over having a cool rifle. i wanted something smaller that i could clear with and it would not be like my full length 16" AR which i built for distance. And where can i source 12.5 parts. i appreciate it

  5. "Everybody knows that 12.5" is objectively the best barrel length" Oh, I didn't realize that everyone had a meeting and came to a consensus on this. Or did you appoint yourself master of the AR and decide for yourself? I didn't even bother to listen to the rest of this drivel, might as well have been another guy saying, ".45 ACP is the best round"

  6. Thank you for being one of the many who feel the need to provide the ATF with all the documentation needed to introduce new rulings
    Apparently Like Comment Subscribe overpowers common sense

  7. Anyone shooting a barrel under 16" in anything besides 300 BLK is a verified glue sniffer. There's no reason to waste your time or money on 5.56 if you don't have at least a 16" carbine. There's no reason to have a shorter barrel unless you're hurling 300 BLK. The 5.56 SBR/pistol world answers a question no one asked.

  8. Ok, I’ve now put too much info inside my head and caused catastrophic data transfer. So, laws aside (I know that’s horrible after you’ve hit on that point several times). What setup should I go with? I will be running suppressed 100%. Warcomp and rc2. I’d prefer bravo company if that helps. I was wanting the 12.5” so that I’d be about the same length as a 16” overall. Should I go 11.5 or 12.5? This will be my only long distance weapon as well. My loadout is an 18.5” 590a1 with talon grip in a backpack scabbard. And a pistol sidearm. The build is intended for straight combat, which, if I get the chance, would rather eliminate from a safe distance, while short enough to run close quarters with the rc2 on it. I know, this entire video explains it all, I would just like a specific parts list and hopefully some real world experience between the 11.5 and 12.5 with rc2 for the long shots. I cannot carry anymore weapons. Aside from the ankle .357 and the armpit .45. Along with the open carried 9mm sidearm. So, a suggested length….with a suggested gas system length, would be what I’m looking for.

  9. I thank you for the pause….and I’m back…had to piss! Anyway, I have a built 16” ar that I am deciding is too long for it’s purpose. For money savings, I wish to just purchase a 12.5” barrel, and swap it out. But need the deets on gas block etc.

  10. Hop, thinking of a 12.5 with a pin/weld can. You mentioned that it was possible. Is there a good option to get a 16 in ish overall length with a welded can? Maybe 13.7 over a 12.5?

  11. Way I look at it, 5.56 with a barrel shorter than 14.5 is just entering the shits and giggles category, which is perfectly fine. I'd argue the cut-off is really at 16 inches, but the M4 has been going strong for so long that it kinda sways my mind. That being said, reason I look at it that way is that for the same platform and the same barrel lengths, there are cartridges you can get that just perform better with that form factor. I.e .300 BLK. I built a 10.5 inch AR in 5.56 and SBR'd it just because I knew it would be a fun toy to have. And it definitely is. But at the ranges it would be considered effective, I'd be better off using a 10mm carbine or just tossing a .300 BLK upper of the same or even shorter barrel length and I'd get better performance. So to me, worrying about the barrel length differences for velocity becomes a moot point since these kind of just fall into the "eh I'm having fun" category and you've lost most of the advantages the 5.56 cartridge provides. Practicality be damned though, I love my 5.56 flamethrower. Definitely gonna get me a .300 BLK upper in the 10.5 range at some point though. Just debating if I go with another side-charger upper again. Lol. Side-chargers are pretty fun.

  12. Hop, can you do a video elaborating on how to use a direct threat suppressor to get over the SBR? Does it have to be welded on there or can it just be a barrel without a muzzle device and the extension of that muzzle is the suppressor?

  13. Why not just have maximum dwell time when unsuppressed and reduce the gas at the gas port? Theoretically it would reduce the percentage change in dwell time when adding a suppressor so there'd be significantly less change in bolt velocity or under/overgassedness or whatever. I thought about this for a while and maybe I'm stupid but idk if I agree with hop on the whole mid length gas thing, assuming you can get carbine length moderately gassed when suppressed.

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