18" Barrel Rifle Length Gas System (RLGS) vs MLGS

[98Z]

Here's an awesome starting point - and there is NO Grendel data in this. It would be great to compile such data, though. Pay attention to the 300BLK 16" carbine gas data. That's max gas port diameter on some of those combos, and close-to-it on others...


AR-15 GAS PORT SIZES

Disclaimer: These are lists of compiled information from multiple sources. While we make our best effort to test and produce these should be considered for reference only. Any time you start messing with the gas port on your rifle you run the risk of destroying the barrel or causing it to be over gassed. It is much better to slowly work your way up to what you would be happy with.

AR-15 Platform 5.56mm

20" Rifle 5.56 0.0935
20" Rifle 5.56 0.096
20" Rifle 5.56 0.098
16" Mid 5.56 0.078
16" Mid 5.56 0.081
16" Car 5.56 0.0625
16" Car 5.56 0.065
16" Car 5.56 0.07
14.5" Car 5.56 0.067
14.5" Car 5.56 0.086
11.5" Car 5.56 0.081
11.5" Car 5.56 0.089
24" Rifle 5.56 0.089

AR-15 Platform 7.62x39mm Conversion

20" Rifle 7.62x39 0.12
20" Rifle 7.62x39 0.125
16" Car 7.62x39 0.078
16" Car 7.62x39 0.081
16" Car 7.62x39 0.0938

DPMS LR-308 Style Rifle

18" Rifle 0.308 0.0960
18" Car 0.308 0.0635
16" Mid 0.308 0.078
16" Mid 0.308 0.081
16" Car 0.308 0.07
16" Car 0.308 0.073
16" Car 0.308 0.076
20" Rifle 0.308 0.0935
20" Rifle 0.308 0.096

AR-15 Platform 300 BLK Conversion Subsonic Ammo

16" Car 300 BLK UNSUPRESSED 0.12
16" Car 300 BLK UNSUPRESSED 0.125
16" Car 300 BLK SUPRESSED 0.106
16" Car 300 BLK SUPRESSED 0.11
16" pistol 300 BLK UNSUPRESSED 0.067
16" pistol 300 BLK SUPPRESSED 0.086
9.5" pistol 300 BLK UNSUPRESSED 0.093
9.5" pistol 300 BLK SUPPRESSED 0.093
8.1" pistol 300 BLK UNSUPRESSED 0.104
8.1" pistol 300 BLK UNSUPRESSED 0.12
8.1" pistol 300 BLK SUPRESSED 0.086
8.1" pistol 300 BLK SUPRESSED 0.093


AR-15 Platform 300 BLK Conversion Supersonic Ammo

16" pistol 300 BLK UNSUPRESSED 0.0625
16" pistol 300 BLK SUPPRESSED 0.059
16" Car 300 BLK UNSUPRESSED 0.099
16" Car 300 BLK SUPPRESSED 0.093
9.5" pistol 300 BLK UNSUPRESSED 0.073
9.5" pistol 300 BLK SUPPRESSED 0.067
8.1" pistol 300 BLK UNSUPRESSED 0.076
8.1" pistol 300 BLK SUPPRESSED 0.067

The 300 Blackout data has been compiled from Micro MOA

[GjGary]

I have a BA 18 RLGS. I had a 4.3oz buffer and would fail to pickup about every sixth round. Put in a 2.9oz buffer and have not had an issue with any ammo, wolf to handloads.
In 3 gun 223 wilde I went back to an 18" rlgs for a smoother less recoil feel. I had a 16 mlgs with adjustable gas block and it eroded the adjusting screw and noticed a more harsh recoil about 6k round count.

[Armadillo66]

I have an 18" straight fluted heavy barrel with a 308 muzzle brake on it. Stoner mid length low profile gas block and stainless gas tube. I had feeding problems at first with all ammo. But then I installed a Wolff heavy carbine spring and a Stoner H2 weighted buffer. Everything functions 100% now and I had real good luck with the 100gr Wolf function and accuracy. I would like to try some 129, 130 or 135gr projectiles to see how they function.

[Vetman1]

Will a mid length gas system with an adjustable gas block have the same recoil as a rifle length system?

Or is it the actual longer length to the gas port size in the rifle length system that leads to the softer recoil of the rifle length system?

[ErikS]

So this shooting "smooth" is a real thing and not a gunnet myth?

It is true.

My son has a 20inch Grendel with a RLGS and I have a 16inch with CLGS. His is MUCH smoother shooting than mine but mine is so much easier to handle when hunting in the woods, it like a good ole' 336 or M94 easy to ruck through the woods.

[Gringoloco]

Having some trouble with cycling issues on my 18" Faxon group buy barrel. I'm running a POF Dictator adjustable gas block (open all the way) and it won't cycle 130 grain federal (will eject but not pick up the next round), however it will cycle 123 grain Hornady American Gunner ammo. I am using E-lander mags and the 4 round meg has trouble loading the first round and won't stay open after the last round about 75%. The 17 round magazine will stay open after the last round of 123 grain Hornady AG but again not with the 130 grain Federal. Brass is ejecting to about the 5 o'clock position and I can see where it is impacting on the brass deflector. Running a standard carbine buffer spring and weight. Since i'm close to POF I dropped the rifle off with them and they seem to be leaning towards the gas port size being too small. If POF determines nothing is wrong with their gas block then I'll throw a non-adjustable block on just to test and see if its a size issue, but I have no issues with the POF Dictator on a 5.56 20" rifle length system.

[LRRPF52]

LRRPF52 - Would you tune a gas block, or the carrier on a MLGS?

I switched over to a JPSCS and put a heavier spring in and I do notice the return to battery recoil on both my PF 18" Neptune VIII and 24" Lilja. Been pondering going one step under the "standard" spring and closing off the gas port a couple clicks.

I also have a Bootleg carrier that came with my 24" Lilja find. That one I have not messed with yet, just dialed in the gas block.

If the port is cut right for the loads you're shooting in MLGS/18", there shouldn't be a need to mess with it.

It it's getting too much gas, too fast, and causing early unlocking, you can:

* Use a reduced load or lighter projectile
* Choke the gas
* Increase buffer weight
* Increase spring weight

The first option will give you the best results. My Lilja 318 with 31.5gr of CFE under a 123gr really is outside of the window it needs to be, with too fast of a cyclic rate. With a max load of CFE223 under the 95gr Controlled Chaos, it's a pussycat, like shooting a Ruger 10/22.

[LRRPF52]

Will a mid length gas system with an adjustable gas block have the same recoil as a rifle length system?

Or is it the actual longer length to the gas port size in the rifle length system that leads to the softer recoil of the rifle length system?

Initial recoil is the same, however the reciprocating mass effects will be a little more harsh on the MLGS vs RLGS.

A RLGS AR15 fed the ammo it was designed for is a very pleasant rifle to shoot.

The shorter gas systems aren't deal-breakers if ported and fed optimally, but RLGS is a very happy place to be for muzzle control.

Only one of my Grendels has RLGS, and I have a pile of them, so that gives you an idea of how important I think this gas system length/recoil management discussion is for me personally.

[Gringoloco]

Dropped off the rifle at POF and they said the cycling was due to the gas block (incorrectly placed port). POF replaced the block and said it should be good to go. Customer service was awesome and they were also kind enough to polish up the M4 feed ramps on the upper receiver no charge. Hopefully this fixes the problem.