Mid-Length Gas Systems and the M4

[99merckx]

I've been running 7.5 gas systems for years, (with no problems), but recently have had a hard time finding quality 14.5 & 16" barrels with anything but mid-length gas ports: Noveske doesn't even offer the "Afgan" in anything other than mid-length, and Bravo offers very little in the way of carbine length gas system barrels. I just hate to have to replace my Knight's Carbine Free-Float RAS just to get a barrel. You've tested the crap out of these systems--so is there any real advantage to the mid-length system, (function wise, not just ergonomically)? Sorry for the long-winded question.

[MP01]

I've run both a lot and the benefit of a middy over a carbine is lower peak gas port pressure and longer dwell time because of the distal location of the gas port.

From my experience I have seen no difference in the reliability of the system either way as long as the proper action spring/buffer weight are used. The middy's shoot a little softer but I shot a Noveske 14.5 N4 barrel until it wouldn't hold groups (it crapped out at about 23,000) and it was a spectacularly reliable gun. I shot a BCM 14.5 out at about 12,000 rds. and it was also as reliable as any rifle I've ever owned. The advent of the middy was an attempt to match the gas system to the barrel length which was originally a problem with the civilian 16" barreled guns with the 7.5" gas system and a port drilled for the 14.5”. The addition of 1.5" from the military configuration (14.5"bbl>7.5"tube) over-gassed an already over-gassed design. The 14.5 over gassing was by design for reliability under adverse combat conditions. The 16" over-gassing on top of that was an oversight and a desire to use existing tooling and parts.

I like and run both and for shootability I favor the middy. In the end they both work fine so pick what yolu like.

[francobx22]

I've run both a lot and the benefit of a middy over a carbine is lower peak gas port pressure and longer dwell time because of the distal location of the gas port.

From my experience I have seen no difference in the reliability of the system either way as long as the proper action spring/buffer weight are used. The middy's shoot a little softer but I shot a Noveske 14.5 N4 barrel until it wouldn't hold groups (it crapped out at about 23,000) and it was a spectacularly reliable gun. I shot a BCM 14.5 out at about 12,000 rds. and it was also as reliable as any rifle I've ever owned. The advent of the middy was an attempt to match the gas system to the barrel length which was originally a problem with the civilian 16" barreled guns with the 7.5" gas system and a port drilled for the 14.5”. The addition of 1.5" from the military configuration (14.5"bbl>7.5"tube) over-gassed an already over-gassed design. The 14.5 over gassing was by design for reliability under adverse combat conditions. The 16" over-gassing on top of that was an oversight and a desire to use existing tooling and parts.

I like and run both and for shootability I favor the middy. In the end they both work fine so pick what yolu like.

Would you say the middy system is less stressful to the weapon?

[MP01]

From the physics perspective, because you are introducing more kinetic energy and at a faster rate (read ftlbs/second) it would have to put more stresses on the rifle. That said I have had no noticeable difference in wear or noticeable parts breakage between carbine and middy systems. The middy is better engineered relative to peak gas port pressure and dwell times and shoots a little softer but both are completely combat reliable and serviceable.

In a barrel to barrel comparison gas port size is always important. The problem comes when people try to compare middy's to carbine and 16" to 14.5". When we establish parameters of application (for instance sport vs. combat) there are much different design features and emphasis. Sport wants less mass and less gas to make a very soft shooting gun (like JP's LMOS) on a combative rifle you want more mass and more gas so the rifle will need nearly a rigid obstruction in the operating parts to stop it from operating. That is why military rifles are over-gassed by design in nearly all models.

.073 is pretty big. I can imagine that with a stock spring it is pretty snappy.

[taekwondopreacher]

Sir,
I hate to drag up an old thread or ask a question that has been asked before, but what is the best way to determine the correct buffer weight/spring combos for standard M4 types? I own a S&W M&P15 and have a LMT standard M4 type rifle on its way. Both have 16 inch barrels. Thanks in advance.

[MP01]

The rule of thumb is no less than H for Carbine gas and 14.5" barrel. I know many Army SOF asets have used H2's and I prefer them. I really like the Spikes H2 with the tungsten powder. I have seen they are much less prone to bolt bounce in full auto guns and soften the recoil/slow down the bolt speed.

I have recently been shooting the VLTOR A5 kit and I prefer it over all other buffer and weight combinations for a combative oriented carbine. I have used it on everything from10.5-20" and with 8.5" 6.8 piston gun as well. It is the softest shooting and most versitile I have ever used in the buffer/spring world. It works equally well in piston guns and actually softens them a lot. I've used it on HK416, PWS, POF and LWRC with great effect.

All said, I would highly recommend the A5 kit. It's all you'll see me with unles I have a self-customized rifle buffer or am running a straight sport gun (think JP Silent Captured Spring).

[WS6]

Once again to re-visit this, but a few years back you wrote in an article extensively about Sprinco springs.

http://www.defensereview.com/m4m4a1-carbine-reliability-issues-why-they-occur-and-why-theyre-our-fault/

Do you still feel the same way, for those of us not running A5's? If so, what is the best way to select the correct spring for the platform? Run the heaviest one that gives reliable ejection? I ask because my platform is a 300 BLK that just came out (Daniel Defense), and there is no "tried and tested data", nor do I have a full-auto lower to test with. Am I SOL until I find someone with a FA lower, or is there a "way" to figure out which spring I need? DD ships with an H buffer.

Anyway, just curious if you were still a fan of the Sprinco in lieu of A5 systems, or if there was another path that you have forged since then?

Thank-you!

[MP01]

I don't have any practical experience nor data on the 300 but am about to begin some testing. I am beginning to lean far in favor of increased static weight and a little less spring tension. Most of my 5.56 guns that dont have an A5 are H2 or H3 buffer and Springco Blue spring. I am a big fan of the Spikes H2 and H3 buffers and for cost efficiencey the DPMS extra-heavy is a bargian.

The key for buffer and spring weight suitability is the rifle when held loosly in your hands and 1 round chambered, empty mag in the well should lock to the rear. Also with a full magazine +1 in chamber the rifle should cycle reliably. The full mag +1 is to validate that the extra friction exerted by the top round of the full mag does not push you in the wrong direction on the reliability scale.