11.5 vs 10.5 Dwell Time?

[Otto Mation]

Would a linear flash suppressor also contribute increasing dwell time? I understand that it would not be as efficient as a traditional suppressor but should there be some benefit? I have a pistol with a 10.5 BA barrel with a Hellfire linear flash suppressor and it has been absolutely flawless since day one. I am wondering if the linear flash suppressor is contributing to the flawless nature of this gun.

[AndyLate]

A muzzle device can produce back pressure, yes. Plenty of folks shooting 10.5" ARs without problems.

Andy

[Otto Mation]

Plenty of folks shooting 10.5" ARs without problems.

Andy

I don't doubt that a bit. Mine is not only the most accurate of all of my AR-15 platform guns, it ejects the brass in a nice neat little pile when I am shooting from a bench.

[MistWolf]

I’m not saying this to pick on you or BCM, but it’s just good marketing. The hard truth is that dwell doesn’t matter much at carbine gas length and 40% dwell time makes most people think it runs 40% better. Dwell time is a real concern at the much lower port pressure of rifle gas length.

The problem with carbine gas is that it exposes things like lack of buffer weight, weak extractor springs, damaged or poor magazines, and crazy port sizes. All things that have been figured out and are fixable, but are known even on the 14.5”. The difference from 14.5” all the way down to 10.5” is just very, very marginal if the above things are taken care of.

This is one of the rare times I wish this site had a LIKE button.

[Leonidas24]

I agree that an 11.5” is a better mousetrap than a 10.3/5”, but only when they’re ported at .069”.

.076” takes all the advantage away IMO.

I knew I'd see you in here and it warms my heart.

BCM could have just as easily hogged out a 10.5 and made it run like their 11.5's do.

[prepare]

So why do so many people say "11.5 is as short as I would go"?

[Wake27]

So why do so many people say "11.5 is as short as I would go"?

Mixture of the Internet saying it’s bad and DD using massive gas ports on the commercial MK18s years ago. I have two 10.3/10.5s, including a DD MK18 from 2020. Super pleasant to shoot and I like them quite a bit. If I was only going to have one shorty, it’d be an 11.5, but I’ve not felt at all undergunned with a 10.5.


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[Clint]

It doesn't work that way.

Punching out the gas port size isn't the same as changing the gas system configuration.

Short dwell configurations are more sensitive to variables in ammo, environment and suppressor use.

BCM could have just as easily hogged out a 10.5 and made it run like their 11.5's do.

Because the 11.5 works reliably over a wider range of variables than a 10.x. due to the better gas system configuration.


We deal with this on a daily basis working up solutions with the EZTUNE gas tubes.

The 11.5 can be setup pretty nicely to run 50/50 suppressed on a single port size.

The 10.5" doesn't do 50/50 nearly as well because the port size can hardly be reduced and maintain un-suppressed reliability.

Then when the suppressor is added, it's way more gassy than an 11.5" setup the same way.

We generally recommend a 10.5 be used as either un-suppressed only or dedicated suppressed, which works great with a small port.

That recommendation is based on having full control over gas port size, so port size isn't the issue, the gas system configuration and dwell time is.

The 10.5 can be reliable at one or the other, but not both with the same port size like the 11.5 or 12.5.

So why do so many people say "11.5 is as short as I would go"?

[prepare]

It doesn't work that way.

Punching out the gas port size isn't the same as changing the gas system configuration.

Short dwell configurations are more sensitive to variables in ammo, environment and suppressor use.




Because the 11.5 works reliably over a wider range of variables than a 10.x. due to the better gas system configuration.


We deal with this on a daily basis working up solutions with the EZTUNE gas tubes.

The 11.5 can be setup pretty nicely to run 50/50 suppressed on a single port size.

The 10.5" doesn't do 50/50 nearly as well because the port size can hardly be reduced and maintain un-suppressed reliability.

Then when the suppressor is added, it's way more gassy than an 11.5" setup the same way.

We generally recommend a 10.5 be used as either un-suppressed only or dedicated suppressed, which works great with a small port.

That recommendation is based on having full control over gas port size, so port size isn't the issue, the gas system configuration and dwell time is.

The 10.5 can be reliable at one or the other, but not both with the same port size like the 11.5 or 12.5.

Thank you for the explanations.

[Todd.K]

So why do so many people say "11.5 is as short as I would go"?

Internet lore, or a poorly set up 10.5”

Clint gives a good explanation of actual considerations but most people don’t own silencers.