I just set up an NFA trust and have stamps pending for a SiCo Omega and to SBR a lower. I currently have a 10.5" pistol build that will be my upper for the SBR but the problem is my rail is 12" and so I need a new one so the Omega can fit. I will want to build a 300 BLK upper because why not and so I am wondering if I got a 12.5" barrel if I would regret it or not. Reason being I have the 12" rail and would just reuse it.
From what I’ve read it doesn’t seem like I would benefit much from the longer barrel in 300BLK and a 9" barrel would be fine. Anyone have a 12.5" barrel and wish they had gone shorter? Any advice in general?
Expected use other than quiet paper punching is maybe some deer or similar sized hunting at 50-200 yards.
In general, you can’t use a 12" rail with a 12.5" barrel+suppressor. Not enough clearance unless your rail is > than 1.5" in diameter and your suppressor goes inside it (like using a DD MFR 12 rail).
The 9" barrel means finding a rail is tough. I ended up cutting a 9" MI SSK rail (actual length of rail is 9.25"). Some other options are the KAC URX 3.1 8", SLR rails @ 8", etc.
Thanks guys, that’s what I needed to hear, will sell the rail.
One thing I didn’t realize is a 12" rail wouldn’t work for a 12.5" barrel and a suppressor. I figured with the muzzle device there would be enough clearance. Good thing I haven’t bought a 10" rail for my 10.5" barrel. That would have been a pain.
If your looking for a quiet 300 blk setup check out the PWS MK-109 upper. The barrel is 9.5. I just got one, I have 500 flawless rounds through with Gemtec 187 gr, I know that is not much mileage but I know it does not like certain ammo. It is stupid quiet with the right suppressor, with the surefire can the db rating was noticeably higher than with the Saker.
With regard to barrel length, I was told for 300 to stay under 10 inches if shooting suppressed. Geissele rails also have a larger rail opening I will measure and edit this post. I can say if getting a 12.5 inch barrel for 300 is already giving you a gut feeling, just go with your gut and stay in the 8-10 range, in the end you will be happy you did.
Barrel lengths vary depending on the end users goals. For general use, I would say that the AAC 9" upper covers most pretty well. Some hunters prefer the longer barrels. So, the OP would have to state if they have a specific goal or general use before being able to recommend a barrel length. Stating “why not?” for a 300 Blackout build implies general use, again it’s hard to argue against just buying an AAC 9" upper for that. If there’s other considerations, then that could change. The A5 system seems to work very well in 300 Blackout, It’s worthwhile to run it with the AAC 9"'.
I’m with the guys above. The 9" AAC is pretty vetted. I’m turning into a 75/77 gr .223/5.56 guy for almost all applications. I really couldn’t see myself buying a longer barreled 300 blk for any reason really. But… If I was buying a 300 anyway it would be for giggles only and the only giggles I think it would offer me would to be a tiny and quite range toy package. You know what they say about opinions.
Why? The shorter barrel is a little handier, but I can’t think of any other disadvantage to a longer one. A 12.5" does have one advantage: since it uses the same pistol-length gas system, it will have a longer dwell time which should give a little bit better functioning with subs. However, most people seem to have no trouble finding subsonic loads that will cycle the 9" reliably. But the longer barrel might give you a little more margin to play with different loads, especially subs with lighter bullets.
For the OP, I’d say get the barrel you want and then see about a rail. Losing a few bucks selling the rail and buying a different one is no reason to take something less than your first choice for the rifle.
I think a 12 might cause subs to go supersonic on occasion? I may be confusing it with 7.62x39 though.
I wouldn’t worry about reliability, the system was designed around 8-10" bbl iirc. It’s been a while since reading up on it, but I think rsilvers was heavily involved with the development of 300blk and suggested sticking to 8-10".
