11.5” Mid Length Barrel Discussion

[Rayrevolver]

The SLR gas block is pinned and a KMR 10 installed. The suppressor will have to be removed to adjust the gas block but not a worry with a direct thread suppressor and intended use of suppressed only.

I will shoot some unsuppressed this weekend to break in the barrel. Hopefully get the stamp shortly.

[FaxonNathan]

The SLR gas block is pinned and a KMR 10 installed. The suppressor will have to be removed to adjust the gas block but not a worry with a direct thread suppressor and intended use of suppressed only.

I will shoot some unsuppressed this weekend to break in the barrel. Hopefully get the stamp shortly.

Looking great with the rail. Nice touch!

[fledge]

Mine is shooting great unsuppressed on the 11th click on the SLR adj block, running titanium BCG and A5H2 shooting federal 55gr. Haven't tinkered with other variables beyond that... Yet.

[tom12.7]

In general, a 11.5" mid gas 5.56 can run well with a dedicated can, but with all the variables involved that can lead to a reduced span of operation compared to a shorter gas system when that system is run without a can. Look at the difference in carrier speeds. Depending on what is used, the span of function could be very limited to what the end user could use reliably.

[FaxonNathan]

In general, a 11.5" mid gas 5.56 can run well with a dedicated can, but with all the variables involved that can lead to a reduced span of operation compared to a shorter gas system when that system is run without a can. Look at the difference in carrier speeds. Depending on what is used, the span of function could be very limited to what the end user could use reliably.

We would strongly disagree, having tested it exhaustively prior to releasing the barrel. Having a longer gas system, by its nature (lower gas pressure, longer dwell), produces longer life.

Yes, it can have a more limited reliable function zone, but we have not seen the bottom limit of it when adjusted and set correctly.

[mig1nc]

The war sport lvoa-s seems to run pretty reliably unsuppressed with an 11.75" mid. So it seems it can be done, and done well

Sent from my HTC One using Tapatalk

[tom12.7]

Maybe, I should have asked what the design intent is for this platform?
Knowing that gassing a 11.5" mid gas barrel without a can with lower port pressure ammunition results in port size range for a given action mass and system. Then also knowing that a 11.5" mid gas barrel with a can that tends to be at the higher cyclic rate change is added with higher port pressure 5.56 ammunition with the same action mass and system, another range of preferable port sizes results. The possible overlap between the 2 types of operation is much smaller in range than what could be had by looking at the same preferable ranges when the gas system for each is reduced somewhat.
What I'm not catching here is how, in the current form of the platform can a 11.5" mid gas 5.56 operate in a wide span of function for suppressed or not without knowing the can (if used?) or the ammunition? When the gas system elongates with the reduced action pressure dwell time, the rapidly depressurizing barrel can work well dedicated to certain circumstances. Making that item for general use may lead to issues, as the end user may use ammunition and cans that do not fit well with their function overall.
I would tend to hesitate against going against a conventional carbine gas 11.5" 5.56 for most without a can. I could see the possible advantages of the carbine gas +1" in a 50/50 type suppressed gun, but mostly for suppressed only. I would be hard pressed to recommend the mid gas length in those without a can, but it has the ability to work very well with a dedicated suppressor.

[FaxonNathan]

Maybe, I should have asked what the design intent is for this platform?
Knowing that gassing a 11.5" mid gas barrel without a can with lower port pressure ammunition results in port size range for a given action mass and system. Then also knowing that a 11.5" mid gas barrel with a can that tends to be at the higher cyclic rate change is added with higher port pressure 5.56 ammunition with the same action mass and system, another range of preferable port sizes results. The possible overlap between the 2 types of operation is much smaller in range than what could be had by looking at the same preferable ranges when the gas system for each is reduced somewhat.
What I'm not catching here is how, in the current form of the platform can a 11.5" mid gas 5.56 operate in a wide span of function for suppressed or not without knowing the can (if used?) or the ammunition? When the gas system elongates with the reduced action pressure dwell time, the rapidly depressurizing barrel can work well dedicated to certain circumstances. Making that item for general use may lead to issues, as the end user may use ammunition and cans that do not fit well with their function overall.
I would tend to hesitate against going against a conventional carbine gas 11.5" 5.56 for most without a can. I could see the possible advantages of the carbine gas +1" in a 50/50 type suppressed gun, but mostly for suppressed only. I would be hard pressed to recommend the mid gas length in those without a can, but it has the ability to work very well with a dedicated suppressor.

Those are the right questions.

To answer them roughly as they were asked:

Design Intent: To create the best-possible shooting barrel for suppressors (as almost all cans are warrantied for 11.5"). From there, we tested and experimented and found the mid works just fine. By going to the longer gas system, it makes recoil more pleasant, reduces wear, and slows down the cyclic rate - all good things.

Yes, a 11.5" mid can span the the reliable operation of most types of ammunition, including 40-grain rounds.

The issue is that most shooters are used to seeing a long section of barrel after the gas port. On a rifle gas system, this is preferable, as the lower port pressure requires more dwell. Going back to mid, carbine, and pistol, the actual amount of barrel needed past the gas port shrinks markedly. In a pistol gas system, you almost do not need any barrel and a "gas trap" system works as the pressure from the powder is so high in and of itself.

Same for carbine, but it needs about a 1" of barrel to operate reliably, and we did the same testing for mid, which is where 11.5" came from. Due to the pressure at the gas port, its all that is needed for mids.

To your thoughts, the window for optimal function is smaller, but the window for reliable function is about the same as most systems. Hence why we chose to open the port significantly, as that gives the shooter the ability to optimize, not relying on our choice of a gas port hole and in worst-case scenario for someone who does not want to go adjustable, it will work without issue (though may be "overgassed")

[MistWolf]

...The other wild card here is also the fact that heavier and slower ammo means more Dwell Time! If I cannot get the 11.5M reliable with 55gr ammo then I will try the 77gr Mk262 clone ammo...

Thank you, Ray- That's the piece of the puzzle I've been missing! Dwell time has nothing to do with it. If it did, slower ammo would result in faster carrier speeds, but it doesn't. It's all about pressure and flow. It's all about the residual pressure curve in the bore after the bullet exits the muzzle. A suppressor slows down the flow of gas after the bullet leaves, keeping the pressure up in the bore at the gas port longer. The same thing happens when the distance from port to muzzle is increased.

Think about it- Ammo that is loaded to lower pressure is slower, which in turn increases dwell time. Yet that same ammo gives slower carrier speeds and even results in short stroking.

Ammo using heavier bullets loaded to the same pressure as lighter ammo results in lower velocities which in turn results in increased dwell time, yet there is no noticeable increase in carrier velocity. With all the experimenting folks on this site do with port sizes, buffer weights and springs, it is in response to ammo pressure, not velocity or bullet weight.

It's clear that it's not about dwell time at all- It's pressure and flow

[FaxonNathan]

That'st's pressure and flow

Bingo. The port pressure at Mid is still quite high, which gives us flexibility on barrel length.

For example, 7.62x39, with lower pressure at that distance is not appropriate for mid 11.5".