Carbine vs mid length gas

[bmash]

Looking at Precision Firearms Bartlein barrels. The 12.5” has Carbine gas while 13.7” goes to mid length gas. I know longer gas systems have some advantages, but with an adjustable gas block is there any reason to add the 1.2”?
thanks!

[A5Blaster Number 2]

Short answer is No.

Longer answer is Maybe.

Depends on if you want to get all the benefits of a adjustable gas block and lowmass system or not.

On game and target inside, reasonable ranges, you won't notice a difference in recoil impolse or effect on target between the two different barrel lengths.

I run adjustable gas and lowmass parts on everything. From 12 inch all the way to 24 inch.

[LRRPF52]

If you’re looking for an overall smaller weapon profile, I really enjoy the 12” Grendels and so does everyone who pulled the trigger on one.

The way I meter the gas in my 12” Grendel suppressed is by running a Bootleg Adjustable Gas Carrier, set on the fully-suppressed position.

I also use an increased power action spring.

Runs like a raped ape:

90gr TNT
100gr ELD-VT
100gr Wolf Steel
110gr PPU
120gr Federal OTM
123gr ELD-M

The first time I shot my 12” Grendel suppressed, I was expecting to encounter problems that I might have to tune, but it ran like a raped ape right out of the gate and felt like, “This is how the AR-15 should be as a baseline.” It was really weird, and pleasantly-surprising.

That was with a tiny buffer too, in the Maxim Defense PDW brace with a short, stiff action spring.

13.7” MLGS will allow you to pin & weld certain muzzle devices so you don’t have to deal with the Mafia. You might see 100fps difference in mv.

[HighDesertDrifter]

LRRPF52 Are you able to run heavier(130s) out of that rig as well? Being able to run full gambit of bullet weights is something I'm interested in. I have an adjustable block and am tuned for 130's but am running into lighter(100 eld-vt) bullets not fully cycling. Am running an h3 and flat wire spring. Been thinking about going back to an h2 as an option.

[LRRPF52]

LRRPF52 Are you able to run heavier(130s) out of that rig as well? Being able to run full gambit of bullet weights is something I'm interested in. I have an adjustable block and am tuned for 130's but am running into lighter(100 eld-vt) bullets not fully cycling. Am running an h3 and flat wire spring. Been thinking about going back to an h2 as an option.

I have not tried 130gr from the 12” yet.

I’m only using a standard carbine 2.9oz buffer.

The last range trip was in the cold, somewhere around 34-42deg F. The 12” ran without flaw.

My .260 Rem AR-10 ran great with 130gr Hornady ELD-M box ammo, but the last round hold open was on the follower, not the bolt catch.

I shot some 100gr ELD-VT through the 18” LaRue in those conditions as well, and I had a lot of short-stroking almost every round, which has never happened to me with Grendel since 2009 across a wide variety of barrel lengths and gas system lengths.

I think the 18” MLGS LaRue did not like the combo of 100gr in colder temps. It has run 123gr flawlessly across cold and hot temps.

I’ve been planning on making it a dedicated suppressed platform anyway with a shorter barrel, so with a can and shorter plug dwell time, it should run lighter bullets just fine.

[bmash]

I ordered an 11.5”. That is what my ultra 7 is rated for. For now I’ll use an adjustable gas block. Per their website, it is an 8 to 10 week wait for the barrel!😡 This will be a dedicated NV / thermal rifle - unless I like it a lot and then I may use for deer as well. Plan to use light bullets. I have a good supply of 90gr TNTs.

[Growler]

I have not tried 130gr from the 12” yet.

I’m only using a standard carbine 2.9oz buffer.

The last range trip was in the cold, somewhere around 34-42deg F. The 12” ran without flaw.

My .260 Rem AR-10 ran great with 130gr Hornady ELD-M box ammo, but the last round hold open was on the follower, not the bolt catch.

I shot some 100gr ELD-VT through the 18” LaRue in those conditions as well, and I had a lot of short-stroking almost every round, which has never happened to me with Grendel since 2009 across a wide variety of barrel lengths and gas system lengths.

I think the 18” MLGS LaRue did not like the combo of 100gr in colder temps. It has run 123gr flawlessly across cold and hot temps.

I’ve been planning on making it a dedicated suppressed platform anyway with a shorter barrel, so with a can and shorter plug dwell time, it should run lighter bullets just fine.

I’ve followed your reports of the 12” Grendel with great interest. Do you know the gas port diameter of that barrel? Recognizing the potential variation in how gas efficient a BCG may or may not be due to manufacturing tolerances, it does sound like you found a sweet spot.

[HighDesertDrifter]

I shot some 100gr ELD-VT through the 18” LaRue in those conditions as well, and I had a lot of short-stroking almost every round, which has never happened to me with Grendel since 2009 across a wide variety of barrel lengths and gas system lengths.

That has been my current experience with the factory offering also and kinda verifies my suspicion the round just isn't quite offering enough boom to fully cycle my current set up. Will wait to see what happens with 90gr tnt handloads before tweaking gas further.

[LRRPF52]

I’ve followed your reports of the 12” Grendel with great interest. Do you know the gas port diameter of that barrel? Recognizing the potential variation in how gas efficient a BCG may or may not be due to manufacturing tolerances, it does sound like you found a sweet spot.

I built 2 of them with the same core components, and both have been reliable since 2017.

I think the ports are .062” off the top of my head. I would have to go look at my notes.

The other one has been fed a steady diet of 8208XBR under 107gr SMK without issue. It has an Ultra 7 on the end. Same Bootleg carrier. Same bolt, same barrel. It has the Maxim Defense PDW RET, tiny buffer, and stiff short spring. Felt like that was how the AR-15 should have been all along when cycling. Very happy behavior with the cyclic rate.

[Growler]

I built 2 of them with the same core components, and both have been reliable since 2017.

I think the ports are .062” off the top of my head. I would have to go look at my notes.

The other one has been fed a steady diet of 8208XBR under 107gr SMK without issue. It has an Ultra 7 on the end. Same Bootleg carrier. Same bolt, same barrel. It has the Maxim Defense PDW RET, tiny buffer, and stiff short spring. Felt like that was how the AR-15 should have been all along when cycling. Very happy behavior with the cyclic rate.

Thanks. Port size is a key parameter—when it’s right, the fine tuning works better. Wish I jumped on the Lilja 12” group buy. Maybe it’s time for a group buy of one

[biodsl]

I shot some 100gr ELD-VT through the 18” LaRue in those conditions as well, and I had a lot of short-stroking almost every round, which has never happened to me with Grendel since 2009 across a wide variety of barrel lengths and gas system lengths.

That has been my current experience with the factory offering also and kinda verifies my suspicion the round just isn't quite offering enough boom to fully cycle my current set up. Will wait to see what happens with 90gr tnt handloads before tweaking gas further.

I was surprised to discover that the factory loading for the 100 ELD-VT was over 100 fps slower than my loading for this bullet. 2530 vs. 2640 out of my 16" Lilja. Hornady left some velocity on the table.