12.5" barrel characteristics ??

[MQ105]

I have run 10.3-11.5" barrels suppressed and non-S for some time, but have fairly recently been trying 12.5. I have noticed what seems to me like a larger difference in operating group speed, and the associated functions, with 12.5 than with the shorter barrels.
For example, I have a Colt SOCOM I cut down to 12.5" with the factory .063" port. It is at the low end of the functionality range without the can, and at the high end with it. It's very over-gassed.
For comparison, I have an 11.5" that I have gassed to be reliable with and without a suppressor. With the suppressor, it runs well, but is not as over-gassed as the 12.5.
I would have thought that the 12.5 would be less sensitive to back pressure changes than the 11.5.

I'm interested in observations and experiences of others who run 12.5" barrels both suppressed and non-S.

[markm]

Although I've never suppressed a 12.5, I can tell you that every SBR is it's own animal. My guess is that there's more to it than just barrel length.

Pappabear and I ported down several SBRs with insertable ports. We shot a bunch of them at the same range trip, and I can tell you that even though all of them showed dramatic performance increases, they all had there own recoil impulses. I've had guns that are more gassy than others for no logical reason. And I've also had a gun that ran perfectly with an adjustable block, but the port snap was so loud it hurt my right ear.

SBRs just tend to have their own subtle varying characteristics.

[Clint]

Interesting.

What's the port sizes on the shorter barrels?

The observed difference could be due to the difference in timing.

[joeg26er]

What gas tube lengths?

I’m running my triarc 12.5 mid length
With slr 7 tuned about 11clicks from full off

[Iraqgunz]

I have a BCM 12.5 Kino and it runs 100% suppressed and unsuppressed. I am certain that markm has shot it at least once or twice.

[vicious_cb]

Interesting.

What's the port sizes on the shorter barrels?

The observed difference could be due to the difference in timing.

Id be more concerned about the design of the can adding too much back pressure. A 0.063" carbine gas port on a 12.5" is very conservative. I like 0.068" for suppressed and unsuppressed use on a 12.5".

[MQ105]

All barrels have carbine length gas systems.
-I have a DD 10.75" that was cut down from 14.5. It has a .0625 insert I made. It runs both S and non-S. Griffin M4SDII. (I can't speak highly enough of this suppressor.)
-Sionics 11.5" with .0650 port, runs well with and without SOCOM RC2. I started with a small port and enlarged until it ran the way I wanted. (Thank you Sionics.)
-Colt 11.5" heavy profile (FBI) with .0635 insert. Runs well with and without RC2.

It's quite true that each barrel/gun combo is definitely unique. I like to port mine so they will run without a suppressor (just in case), cold, dirty, and dry. The difference suppressed is notable, but not too bad. This 12.5 borders on violent with the can, yet barely runs without it. It runs 100% thus far, it's just...super snappy. All uppers run with the same lower specs: A5 RE, A5H2, Tubbs SR-25 flat spring. The difference from non-S to S seems much greater than with the shorter barrels.

[Clint]

Hey Mike,

Do these barrels have full reliability with all ammo unsuppressed?
i.e. lock back with loose hold



All barrels have carbine length gas systems.

-Sionics 11.5" with .0650 port, runs well with and without SOCOM RC2. I started with a small port and enlarged until it ran the way I wanted. (Thank you Sionics.)
-Colt 11.5" heavy profile (FBI) with .0635 insert. Runs well with and without RC2.

All uppers run with the same lower specs: A5 RE, A5H2, Tubbs SR-25 flat spring.

[MQ105]

Yes, but...

I have not fired any steel cased ammo. Wolf gold, AE223, Fed LC 223, and all 5.56 I have tried have full functionality without a suppressor.

[MistWolf]

You've got a few variables throwing monkey wrenches into the works- different models of suppressors, gas tube fit, gas ring fit and extra distance from gas port to muzzle...

[CoryCop25]

I have a 12.5" rifle that started out as an M-16 with a DD 12.5 barrel an AAC Mini4 suppressor and A5H4 buffer. Since I was issued this rifle and had the opportunity to shoot it anytime I wanted, I shot the DD barrel out in about 16K rounds. I then replaced it with a Noveske CHF barrel. I cooled off with the full auto fire and the Noveske shoots way smoother (the DD was super over gassed) with and without the suppressor.

My suggestion to you is to buy a true 12.5 barrel (I highly recommend the Noveske CHF) and don't cut a barrel down and make something out of something it wans't designed to be.

[diving dave]

I have a BCM 12.5, with the can it seemed a bit "snappy" in recoil but no function issues. I added a Bootleg adjustable carrier and made a huge difference.