Gas Port Spec - 18" RLGS

[cory]

We're trying to determine the best gas port diameter for an 18" barrel with a RLGS.

I understand some of the members on here have ran this system with great success after enlarging their gas port size.

Could y'all share your experiences with it and the gas port size you're using?

[LRRPF52]

Here's what drifter posted in the Lilja Group Buy Thread:

I shoot an 18" with RLGS, but it's a Satern 20" that was cut back. Don't recall the port size, and I didn't enlarge it. It's a little fussy with fast powders and light bullets, especially if it's gone ~150 rounds or so without cleaning the BCG. If Bill A says that 0.005 changes the 16" with MLGS from fussy to reliable, I would guess the same principle might apply to an 18" with RLGS. In other words, ~0.098 to 0.100 might be a reasonable estimation for optimum port size on an 18" with RLGS.

FWIW, I had a BHW (264 LBC) that was 18" with MLGS. IIRC, the gas port was ~0.082, and it ran beautifully with a standard gas block. Note that the barrel is 2" longer than a 16", and the gas port is ~0.004 larger than Bill A's recommendation for 16", and this is very close to the 0.005 difference mentioned in the previous paragraph.

A Grendel with RLGS and rifle-length buffer system is a smooth operator, and a joy to shoot.


ETA- Some additional thought... Another way of looking at this is the distance between gas port and muzzle. If you know the optimum port size for 16" and 18" with MLGS and 20" with RLGS, you might could use the measurement from port to muzzle in each of those to determine a formula to apply to an 18" with RLGS. Might be worth running the numbers to see if they jive with the previous estimate in this post. -And my apologies if it turns out to be a waste of time...

[cory]

Alright so do we want to go

18" RLGS: .082"
18" MLGS: .078"

[dmsims21]

Alright so do we want to go

18" RLGS: .082"
18" MLGS: .078"

I think that is too small. I saw posted that .094 was recommended for a 20" RLGS.
I think drifter is suggesting adding .005 to he gas port diameter when the gas length stays the same, but the barrel is shortened by 2".
Adding .005 would give us .099

[Hank Rearden]

My 18" RLGS had a .082 from McGowen, and had problems cycling the factory loaded 123-Amax.
After opening it up to .094 it functions without fail with the factory loads, as do all of my hand loads using a 123gn pill
Just my 2cents

[cory]

My 18" RLGS had a .082 from McGowen, and had problems cycling the factory loaded 123-Amax.
After opening it up to .094 it functions without fail with the factory loads, as do all of my hand loads using a 123gn pill
Just my 2cents

Have you fired any 100gr loads out of it?

Do you know what velocities your getting?

[cory]

I think that is too small. I saw posted that .094 was recommended for a 20" RLGS.
I think drifter is suggesting adding .005 to he gas port diameter when the gas length stays the same, but the barrel is shortened by 2".
Adding .005 would give us .099

I ran those numbers by Dan with the others we seem to agree on. He was on board with the rest but thought that .098"-.100" seemed excessive. I tend to agree, but if we have some field data to back it up I'm gtg with it.

[Hank Rearden]

Have you fired any 100gr loads out of it?

Do you know what velocities your getting?

I haven't worked on anything other than a 123gn yet.
After working with 4 different powders I've settled on
31.3gn of CFE-223 W/wolf SRM primers MV of 2508fps
Best Group .579inches at 100YD

Link to thread

http://www.65grendel.com/forum/showthread.php?6219-Nosler-123gn-Custom-Competition-over-3-different-powders&p=64929#post64929

I Really enjoy the way an 18" barrel handles, and with 2500ish muzzle velocity it is capable of any task i will use it for.

[cory]

I haven't worked on anything other than a 123gn yet.
After working with 4 different powders I've settled on
31.3gn of CFE-223 W/wolf SRM primers MV of 2508fps
Best Group .579inches at 100YD

Link to thread

http://www.65grendel.com/forum/showthread.php?6219-Nosler-123gn-Custom-Competition-over-3-different-powders&p=64929#post64929

I Really enjoy the way an 18" barrel handles, and with 2500ish muzzle velocity it is capable of any task i will use it for.

That's absolutely smoking. You're going to make me rethink my order.

[LRRPF52]

If we have the option to go with the proven 18" MLGS, we need to use the port diameter that has shown to be reliable. With the extra dwell time compared to a 16" MLGS, it should be similar or smaller than a 16".

I watched BjornF16's 18" MLGS Grendel burn through cases of ammo for 3 days, and I don't remember any hang-ups. The 18" MLGS runs the system harder than a 16" MLGS if the ports are the same diameter.

[cory]

So what is the proven 18" MLGS port size?

[Drifter]

It can be a challenge to select a port size that pleases everybody. A system "on the edge" that routinely runs on CFE might have trouble with 8208. Hornady factory loads fall somewhere in the middle. Not to mention the variables of BCG, buffer weight, buffer spring length / strength, etc.

An 18" with RLGS and 0.094 port will probably be fine with Hornady factory loads and slower powders. If someone plans to burn mostly 8208 in an 18", a MLGS might be a better choice.

[dmsims21]

I will take the 18" Lilia 310 profile with an MLGS if Dan will make it. Otherwise, I am fine with the 18" RLGS and .094ish gas port. I don't plan on shooting lighter than 107gr bullets.

[CPT.CRAZY]

I would prefer to see the gas port on an 18 rlgs .098-.100 , maybe slightly larger and plan on running an adjustable block.

[Hank Rearden]

I would prefer to see the gas port on an 18 rlgs .098-.100 , maybe slightly larger and plan on running an adjustable block.

I'm am certainly no expert on this subject, but with the .094 port on my RLGS I've had to adjust gas block down to about 50%. Without this my brass was showing signs of premature extraction (huh,huh he said extraction). The dwell time was obviously too short and the extractor was literal tearing pieces of brass from the base of the cases.
Any more gas and the block would be working double duty and erosion would be certain.

I agree with LRRPF and suggest that a MLGS would be the most reliable.

There is one glaring difference here though. The Lilja barrel is .88 inches longer and that could put it in just the right sweet spot to function correctly with the rifle sized gas port.