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

[BluntForceTrauma]

There are probably very few 18" 6.5 Grendel barrels in a Rifle Length Gas System (RLGS) as opposed to a Mid-Length Gas System (MLGS).

RLGS is supposed to be smoother shooting.

MLGS is supposed to be more reliable with more bullet weights.

True?

Not true?

Opinions?

Experiences?

[bj139]

I have a Ballistic Advantage 18" barrel with a RLGS.
It will not cycle with Wolf steel ammo. It ejects but will not cycle back enough to pick up a new round.
I have not shot it enough to determine if it might get better with break in.
I will not buy another 18" barrel with a RLGS.

[BluntForceTrauma]

You happen to know their gas port size? I think that is the relevant issue.

[bj139]

I don't know the gas port size. I do know LRRPF52 recommended drilling it a bit larger. I will look up the past thread when I get around to it.

[BluntForceTrauma]

Did a little Googling and one reviewer says it's 0.092-0.093, which is about the same as a 20" RLGS. So, I'd venture that it's slightly undergassed.

[Kswhitetails]

From what I've been READING, the 18 MLGS system can be hard on the firearm components by increasing cyclic rate due to the lower dwell times. This also may be because they increase the port size for the shorter barrels. Haven't needed another barrel yet, so haven't done any specific research. PS would know. He's been commenting about this issue lately. I think he referred to experience gained in finding the reason for system failures in the field. I have been remembering things I read along the way incorrectly lately.

This for the next group buy design?

[BCHunter]

My only experience is with the odin works 18" it has an intermiate length gas tube, in between a mid and rifle length.
The only ammo it hasn't cycled is started charge reloads of imr 4198 of 23g, 23.5g and 24grains with the 95 grain vmax.
I have not tried wolf in it and don't intend to.

When starting my build I was looking for an 18" MLGS but didn't find many available in my price range. I also wasn't aware of 18" being harder to tune the gas system. Coming from standard AR's were I have 2 18" MLGS that run great in .223 wylde.

[dpete]

My Odin Works 18" is Intermediate gas and shoots great. It seems they split the difference between mid and rifle length.

[Crusty]

Hey BFT (in a somewhat related matter) my Satern 18" mid gas barrel with the .093" gas port that cycled crazy fast (and misfed and abused my brass) now performs normally since I made a restrictor that cuts the gas back to Bill Alexander's .077" spec. (with no other changes).

In a typical low pro gas block there's an internal bore hole connecting the barrel and the gas tube and I made a restrictor from a stainless bolt that fits snugly into that bore.

[Jakegsxr11]

I run a Brux 18" RLGS (Rifle-Length Gas System) .094" gas port with JP Adjustable gas block, don't know how far open, but there is some left, I tuned it from closed . It functions perfectly with Hornady SST and Black, I have no intentions of running wolf.

[98Z]

Did a little Googling and one reviewer says it's 0.092-0.093, which is about the same as a 20" RLGS. So, I'd venture that it's slightly undergassed.

I've got the Ballastic Advantage Mk12 profile barrel - 6.5 Grendel Mk 12 SPR profile, heavy stainless, rifle gas, measured out a 0.100" gas port diameter.
Only shot Hornady Black through it, and my handloads. Never a hiccup, not once. It does shoot quite smooth.

Also have this one, but the build isn't finished yet, and the barrel is unfired. Faxon midlength data: Faxon Firearms 6.5 Grendel gas port info: Match Series- 18" Gunner, 6.5 Grendel, midlength gas system, 416-R, 5R, Nitride, Nickel Teflon Extension - Gas Port diameter = 0.077".

[grayfox]

Sold my 18" 6.5"ARP" barrel/upper, it was too finicky for me, rifle length gas. Didn't know at the time about gas port sizes, it was 50-80 ft/sec faster than expected but I couldn't get it to behave brass-wise. So I sold it.
The issues may have been the chamber or the port size or the RLGS, anyway I just sold it and started over. Don't want another RLGS 18-er, I can get an adjustable gas block to help with cycling if the port is too big.

[LRRPF52]

JP uses RLGS 18" Grendel barrels and they work fine.

Biggest thing you have to look at with RLGS 18" Grendel is lighter projectile weights and loads, and what will cycle.

18" MLGS has a lot of plug dwell time since there is so much more barrel in front of the gas port, making the port pressure dwell longer, causing faster cyclic rate and more prone to early unlocking.

18" MLGS AR15s even in 5.56 are harder to suppress for this reason, let alone 6.5 Grendel with its higher case capacity.

Precision Firearms introduced an Intermediate Length Gas System 18" option a number of years ago.

Several years later, Odin Works introduced an 18" ILGS Grendel as well.

I have found that 18" MLGS .076" port will run Federal 90gr TNT well.

Medium-slow powder loads (like CFE223) pushing more towards max with 123gr noticeably increase the cyclic rate and recoil, as well as carrier bounce with 18"/MLGS/.076" ports.

95gr Controlled Chaos loads handle the best as far as cyclic rate and recoil in my Lilja 318 Wasp group buy barrel build with the JP SCS.

I need to tune my SCS to be able to handle 31.5gr of CFE223 under a 123gr AMAX, because the carrier just bounces hard off the extension during the return-to-battery cycle.

That rifle would be a great candidate for the Bootleg Adjustable carrier actually.

With RLGS 18" Grendel/.094" port, 100gr TTSX will run well since it's got a longer bearing surface and is harder to swage into the rifling.

[keystone183]

The original lilja group buy barrels, one of which was 319 i believe, were ~19" and ML. Not nearly as pleasant to shoot as a buddy's RLGS 18" Criterion. I vote 18" RLGS every day of the week and twice on sundays.

[BluntForceTrauma]

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

[VASCAR2]

I bought a midlength Faxon 16" group buy barrel and have since bought an 18" Faxon group buy midlength barrel. My 18" Faxon seems to have the ideal gas port diameter for shooting thus far. Since I completed this build in January I have not shot it in hot weather.

So far my 18" Faxon has a smoother feel when firing than my 16" midlength Faxon. I added an H-2 buffer to my 16" Faxon which has proven reliable. The 16" barrel threw the spent cases to 3-4 O Clock but the recoil seemed harsh compared to my other 6.5 Grendel AR-15's so I tried the H-2 buffer. I don't run suppressors but from my intial shooting I really like the way the Faxon 18" barrel shoots. So far I'm completely satisfied with both my Faxon barrels. One difference between my 16" Faxon build and my 18" Faxon is the Bolt carriers. I'm using a Precision Fierarms 6.5 Grendel BCG which is really a nice slick carrier with my 16" Faxon. I'm using a Nitride PSA carrier and Monster bolt in my 18" Faxon. I'm really surprised the 18" Faxon feels smoother shooting than the 16" Faxon considering the 16" has the more expensive better finished PF bcg.

[98Z]

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

I believe so, yes. Look at the 14.5" (real) M4 and M4A1 guns,with carbine gas. Then the 16" legal AR15 barrels as a comparison - with carbine gas. Harsh recoil, and the "advent" of the midlength gas system, to tame down the 16" barrels. The "legal-length" barrel extended for the masses, and the gas system did too, eventually. Enough gas pressure, through gas port sizing, but reduced port timing (dwell time), created "less harsh" recoil, on the 16"midlength. Then, we move the midlength gas to the 14.5" barreled carbines - even better yet.

Right now, I only have 2 Grendels to compare - 12.5" carbine gas gun, and 18" rifle gas gun. The 12.5" carbine gas is running a standard carbine-weight buffer, but in a LAW Tactical folding stock adaptor, so the BCG has that extension in it, making for a heavier recoil system. The 18" rifle gas gun is running the VLTOR A5 recoil system, with their H1 buffer, 4.56oz., about an "H2 weight" for a standard carbine buffer.

Both those recoil systems will affect the felt recoil, and BCG speed... but that 18" rifle gas gun shoots very nice - just like the Mk12 Mod 0 and Mod 1 builds in 5.56. It's a nice Grendel.

An 18" rifle gas system for the Gren will do it's job - if the gas port is sized right. My BA Mk12 profile barrel is sized at 0.100". So far, the only thing I've fed it is Hornady 123 ELD-M projectiles, either in factory Hornady Black ammo, or my handloads. I load the same projectile. I'll be experimenting with 130gr Sierra Game Kings shortly, and I've got a box of Barnes 120gr TSX to figure out.

[Sticks]

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.

[Joseph5]

I am not 100% sure because I did not get it out and measure it but I believe that it is a mid length/intermediate system. The LaRue is very soft shooting. I think, and I may be incorrect, that matching the port size to the gas length is what is important.

[98Z]

I think, and I may be incorrect, that matching the port size to the gas length is what is important.

You are correct in that. Gas port size has to be matched to: gas system length AND overall barrel length. That's what determines the gas port size. Almost any system is quite viable, if the gas port size is right. Been through this too many times with the gas gun .308s. You wouldn't believe how many times you'll hear that a rifle gas 16" 308AR isn't possible - but it is, very possible. There are very, very few manufacturers that offer that profile, but it is very workable, and quite the nice-shooting system. It really is, all in the gas port sizing...

Just matching gas port size to a gas system length won't work, because that does not account for dwell time - or, port timing. Example: .085" gas port diameter for a 16"" barrel with carbine gas, is NOT going to work for a 20" barrel with carbine gas. Make sense?

For reference, you better have a gas port diameter of 0.100"~0.105" on a 16" rifle gas.308 AR. You won't have a functional, reliable 308 if that gas port isn't close to that.