Anyone played with a 12.5" Mid-length Gas System?

[Steve-0-]

I messed with an early warsport upper that was proprietary as all hell. I ended up cutting down an FN 14.5 middy to 12 and opening the port to .096 and it would cycle PMC on an H Buffer with an A2. That being said, I didnt feel any real advantage in recoil over a properly ported 12.5 carbine length upper. It was minimal.

[Junkie]

All of the dissys I've seen were all carbine gas, but had a FSB installed at the rifle position to make the sight radius as long as possible.

Both styles are available, many people call the style you speak of mock dissipators. I suppose a Colt 605 would have been a better example.

[scooter22]

BCM 12.5" Kino and be done with it

[cgjane]

BCM 12.5" Kino and be done with it

THIS. If all you are after is more rail.

[SteveL]

How does the A5 or rifle system reduce the carrier velocity, is it just the heavier buffer? From what I'm seeing a rifle buffer is 5oz, while an H3 is a little heavier at 5.6oz. For a given buffer weight, how does the longer body of the buffer (the only significant difference I can find) change how it fires, does it have to do with the weights having more wiggle room in the buffer?

It also has to do with the spring rate and length. The A5 system utilizes a rifle action spring rather than a carbine spring. As I recall the spring tension is more consistent throughout the cycle making for a smoother recoil impulse and slightly slower carrier speed.

[Jmacken37]

THIS. If all you are after is more rail.

I'm not after more rail, but do like the recoil impulse of a middy better than a carbine length gas system.

[tom12.7]

It also has to do with the spring rate and length. The A5 system utilizes a rifle action spring rather than a carbine spring. As I recall the spring tension is more consistent throughout the cycle making for a smoother recoil impulse and slightly slower carrier speed.

In the balance of spring and reciprocating mass for a given system, the required mass is different when comparing the carbine type action spring and the rifle type action system. The rifle action system would need the higher mass to retain the balance compared to a carbine type. The higher mass means that the system will operate at a lower rate. That lower rate means reduced carrier velocities. The lower carrier velocities means it takes more time for the camming events to occur. The lengthened time of those events allows a quickly depressurizing barrel to depressurize even further. The reduction of pressure means many other things occur, reduced camming tension, reduced unlocking tension, etc.
When comparing rifle action types to carbine types, there is no standard mass, just spring type. The carbine system isn't dedicated to a 3.0 ounce buffer, nor a rifle to any particular buffer weight. For either system, a balance has to be made for either to be proper for those systems. For the vast majority, a properly balanced rifle action system will have a broader range of function over the carbine type action system.
There is some more merit to the A5. The spring inside the buffer stacks the weights on the carrier side, and leaves a sprung space on the bumper side. It may not sound like much, but it improves the consistency of initial carrier movement very well. The variation, when compared to unsprung buffers is noticeable.

[tom12.7]

Forgot to add that carbine gassed 12.5" guns run really well. 12.5" carbine +1" gassed is about as far as I would go in my experience. Add a can to that for me could be a +1" gas gun for 50/50. Most 100% suppressed can run well 12.5" mid gas. Really, the end users goals determine the base needs of the platform.

[Clint]

There is some more merit to the A5. The spring inside the buffer stacks the weights on the carrier side, and leaves a sprung space on the bumper side. It may not sound like much, but it improves the consistency of initial carrier movement very well. The variation, when compared to unsprung buffers is noticeable.

I've come to believe that this "biasing" spring actually is more important than most people think.

Afaik, the original AR10 buffer and the new H6 buffer have no extra space for the weights to move, which is one way to keep the weights pressed against the carrier side.

All the other buffers (rifle,CAR) have extra space inside for the weights to move and their initial positions before firing are somewhat random, which causes inconsistent cycling.

[Clint]

I like the recoil impulse on a 14.5" mid-length gas system better than the recoil impulse on a 14.5" carbine-length gas system.

Would I like the recoil impulse on a 12.5" mid-length gas system better than a 12.5" carbine-length setup?

It may be helpful to offer some comparisons.

The 12.5 MID has similar but a little worse timing than the 10.5" CAR.
IMO, Both of these have too little power time vs gas delay to be reliable in all conditions.
Notice how BCM does not even offer a 10.5" CAR barrel? *This is a clue.*

The 14.5 MID has near ideal timing and runs similar to the 11.5 CAR.
The reputation of these two configurations is very good.

The 12.5 CAR has good timing, just like the 16 MID.
The reputation of these two configurations is also very good.


Given the choice of any SBR barrel config, I'd select 11.5" CAR all day long.