308 sbr gas system length

AR/M4 Beyond 5.56/.223
1

i am starting to narrow down my build and getting hung on the barrel decision.

i originally wanted a 13.5 middy, but no one makes one. aero makes a 12.5 carbine. i know it’s going to cost a bit more money (extra cost for the barrel and the cut/thread job), but i am considering getting a 16" middy and having it cut to 13.5 to get exactly what i want. any reason not go with a 13.5 middy? my reasons for the 13.5 middy is a bit more velocity and a smoother operating gas system. or am i being too picky?

build details:
aero m5e1 enhanced upper
aero lower
SLR agb
saker 762

2

In case you weren’t aware, if you use an A5 RE with a 308 AR, it needs a carbine length buffer. This is due to the extra length of the 308 carrier.

3

Yes, and vltor also suggested a certain armalight spring as well.

4

Unsolicited advice, but I highly recommend against going under 14.5 with .308, and under 16" only if the user has a specific niche application and/or is shooting very light projectiles at at least moderate velocity.
Quite frankly (again, unsolicited, I know) if I had a need for a 13.5" .308, I’d buy a SCAR-H and the CQC barrel. I promise that it will save you a lot of headache.
Dropping under 16" of barrel makes a significant detrimental effect to ammunition performance, and while I like my 14.5" SR-25, I am demonstrably more efficient with my 16" guns.
Now, change that to a 13.5"-14.5" 6.5mm CM or .260 Rem and I will sing a different song, but that’s better left to another thread.

5

i have a scar17 and i’m not really warmed up to it for some reason. i played with a buddies 12.5 308 SBR and liked it much better over the scar17. i have a seekins sp10 and like that much better as well over the scar17. i know, different animals and different uses, but im preferring the AR large frame animal.

6

I gotcha, just warning that 7.62 DI guns under 14.5" tend to be finicky.

7

Would you say the 14.5" SR25 uppers are finicky at all? If you don’t mind, can you elaborate on how you are more efficient with the 16" variants?

Thanks in advance

8

Luckily the 14.5 SR-25s benefit from the last few years of focused system optimization, and they run right along with the 16" guns (and better than even our legacy models of 16" guns).

9

That is good to hear, thanks.

Was there a thread here specific to the 14.5" SR25 uppers? I thought I read through it a while back, and now I don’t see it when I search. I had a few more questions specific to the 14.5" vs 16", but don’t want to hijack this thread.

10

Hijack away my friend

11

Thanks!

Here it goes:

-Starting with a 16" ACC, would you recommend to change buffer weight when swapping for the 14.5" upper?

-If using the rifle suppressed full-time, would you recommend switching to a MAMS over the flash hider? The suppressor I was looking at was the CRS.

12

The 14.5 ACC/CC is designed to operate with the standard SR-25 carbine spring and 2H buffer (included with the upper kit).
There is no appreciable functional difference between a flash hider and the MAMS when under a suppressor. The MAMS will serve to protect the first baffle a little more than a flash hider, but the CRS will last for tens of thousands of rounds even with a FH.
If precision is a priority requirement for the user, I do recommend flash hiders in general.

13

Perfect, thank you.

One more thing, and I know this gets into ballistics, but would would the suppressor add velocity in any way?

In other words, does it basically act like an extension of the barrel extending the rifles effective range? The furthest targets I’d see myself shooting would be 600 - 800 meters away. It would see most use hunting hogs.

I’m still a ways away from buying anything, but just trying to learn as much as I can before jumping in.

14

Increase in velocity will be minimal. I haven’t cronoed any of my gassers yet. My bolt gun, gap hospitaller 308, only saw a 10fps increase with a TBAC ultra9.

15

Freebore boost (velocity increase attributable to a suppressor) is variable, but with KAC suppressors at least, only runs in the 5-20 ft/s area.

16

Went with the BA 12.5 carbine gas. I’ve taken it out once, out about 100 rounds thru it. It HATES ppu. When I was getting on paper at 50, I was getting 4" groups. I thought to myself, “shit…here we go…”. Put some fgmm in it and all was good.

Only took a few rounds to get the gas block set. As a “gas to face” test, I ran 2 full mag dumps of ppu to see how gassy it is. I am pleased to say it’s not gassy at all. Just lube splatter.

17

i was hoping to hear how the 13.5" mid gas barrel shot but it looks like you got a pretty nice shooter with the 12.5" carbine barrel

did you find a sweet spot with the gas block or do you have 2 settings , one for unsuppressed and one setting for when you attach the can

18

if i get some extra money i feel like wasting over the summer, i’ll do the 13.5 middy.

i have zero plans to shoot unsuppressed, so no i do not have a setting i use for both.

19

i tried an adjustable gas block on my 12.5" 308 and could never find a happy medium

i got lucky and scored a noveske switchblock for it a few months back , i still need to get out and try it out

i think my next 308 will be an mws with a 13.5" barrel. that’s why your build had my interest

20

thank God for this thread. I’ve been back and forth on "SBR 308’s for awhile. I’ve always thought a 13in FAL would be an awesome truck gun but not for the price. 308AR’s are getting decently priced and, I know I’m about to get shunned to hell and back for this, but I picked up a Diamondback 308(oh God I know, DB!!!) and swapped the barrel to a BA Hanson 16in and topped it with a Trijicon Accupower 4-16. I wasn’t expecting much from the gun for the price, but this damn thing eats everything I put thru it and with FGMM 168gr ammo, its bug holing at 100 and now that I’ve been able to get it out to 600, I’m damn pleased with the gun.

DB makes a 13in 308 “pistol” that I’m contemplating getting as a starting point and SBR’ing it to have that truck gun I’ve been wanting. If I don’t do that, I’m just gonna build a 11in 6.8 upper as I’ve got plenty of that ammo for the 16in 6.8 hunting rifle I’ve got.

I still like the idea of 13in 308 tho. Something about 150gr .30cal bullet thumping away at the asshole who made me get the truck gun out just puts a smile on my face lol