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Talk to me about gassing and buffering LR-308

Montany_Logger

Montany_Logger

Private
Minuteman
Dec 19, 2022
16
5
Missoula, MT
Hello all. I'm building my first ar-10 and had a few questions to bounce off the wall. I have built one ar-15 and I pretty much just went with a carbine gas system and stock Aero carbine buffer kit and it works great. I plan on taking my time with this build and doing it right. I'm starting to gather from online reading that an adjustable gas block is very advantageous if not mandatory. I'm planning on getting an 18" Faxon barrel (rifle length gas .750 index) and BCG, a Superlative Arms bleed off adjustable gas block, JP gen 2 silent capture, and some sort of decent carbine buffer tube. I figured this would give me the most adjustment on both ends of the cycling system. Am I over thinking this? Would I be better served with an A2 style buffer tube? I'm building all of this on a Grey Ghost Precision receiver set. What am I missing? What would you do different?
 
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Oh, I won't be running this suppressed at any point in time. This will be a multi purpose rifle so I am pretty certain I want to use an 18" barrel
 
I'm running a JP SCS with the H2 weight setup and the JP LMOS BCG with an SLR adjustable gas block and my rifle is unbelievably smooth. I think you'll be fine, just dial in the gas block to lock the BCG back and run it with H2 or H3 buffer set up. There have been a few other threads that recommended this setup for prolonging brass life.
 
16” rifle gas criterion barrel and an Armalite AR10 carbine receiver extension kit doesn’t require an adjustable gas block.

Same setup with an 18” ARP 308 rifle gas barrel worked great as well.

Rifles set up on the ragged edge of reliability when clean and cool can choke when they get dirty and hot. Give the gun enough gas to run.
 
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Noted, I had heard otherwise. I was only planning on going that direction because the criterions can be hard to find
 
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The JP SCS is designed to work in a standard AR-15 carbine receiver extension. They include a spacer that you use if you're using an A1/A2 rifle length RE. You can also use an intermediate (A5) length RE if you cut the spacer down. So functionally, the JP SCS works the same no mater the RE length. It comes down to what stock you intend on using (fixed or adjustable), then look into specific RE brands features/quality.
 
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Truthfully you do not need an adjustable gas block if you are not running suppressed, an adjustable gas block just leads to more additional problems down the line, i know that may not be cool but somebody tell me otherwise.
 
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My advice is don't do it

Diy large frames are a waste of time and money. Unlike the posh factory guns you can't get your money back after BTDT.

But if you must . . .

Rifle length 16" , h2 buffer, the lowest back pressure can you can find (oss / sandman k). Skip the JP bs except maybe the scs if you just have to buy a silly gadget.

Douse it with motor oil and don't screw around with different loads or steel crap.
 
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Cr1775 said:
Truthfully you do not need an adjustable gas block if you are not running suppressed, an adjustable gas block just leads to more additional problems down the line, i know that may not be cool but somebody tell me otherwise.
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It is possible not to need an AGB on large frames, depending on the cartridge, barrel length, gas system length, gas port size, dwell, operating system mass, buffer weight, ammo, etc. Unfortunately, there is no spec for these components or their combinations. My experience, the smaller the caliber, the more likely the need for an AGB. What chamberings do you have in your large frames?
 
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Cr1775 said:
Truthfully you do not need an adjustable gas block if you are not running suppressed, an adjustable gas block just leads to more additional problems down the line, i know that may not be cool but somebody tell me otherwise.
Click to expand...
…Somebody tell you otherwise?…

You’re wrong
 
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msgriff said:
It is possible not to need an AGB on large frames, depending on the cartridge, barrel length, gas system length, gas port size, dwell, operating system mass, buffer weight, ammo, etc. Unfortunately, there is no spec for these components or their combinations. My experience, the smaller the caliber, the more likely the need for an AGB. What chamberings do you have in your large frames?
Click to expand...
Yes, it is possible to not need an AGB on large frames…

I’m just guessing here…but I’m assuming everyone who is suggesting to NOT use an AGB, does NOT reload for their large frame AR?…
 
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Earnhardt said:
Yes, it is possible to not need an AGB on large frames…

I’m just guessing here…but I’m assuming everyone who is suggesting to NOT use an AGB, does NOT reload for their large frame AR?…
Click to expand...
The only issue you're going to run into when reloading is being under gassed because it's damn near impossible to get the same pressure/muzzle velocity that quality match ammo provides, and at that point in becomes a mass regulation issue.
 
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You can either adjust the AGB or mess with the buffer weights. To me, it's much easier and faster to adjust the gas block.
 
SalomonQST99 said:
You can either adjust the AGB or mess with the buffer weights. To me, it's much easier and faster to adjust the gas block.
Click to expand...
My ARs all run fine, i load to my rifle and they run good.
I have watched others at the range using adjustable gas blocks, they seem to be constantly fucking with them and never get them right .
I guess do what you want.
 
Cr1775 said:
I have watched others at the range using adjustable gas blocks, they seem to be constantly fucking with them and never get them right .
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That's it? I was hoping for definitive proof of AGB's causing problems down the line. Or even a single bad personal experience. The things that happen at public ranges are a strong argument for eugenics, not against AGB's.
 
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Also advise against building your own. I built mine, and spent way too much time and energy chasing gas and buffer/spring combos and gas lengths. Unless you are bent on doing it yourself, which I totally get; get into a ready to go platform and enjoy.
 
TonyTheTiger said:
That's it? I was hoping for definitive proof of AGB's causing problems down the line. Or even a single bad personal experience. The things that happen at public ranges are a strong argument for eugenics, not against AGB's.
Click to expand...
It took no more than 5 minutes at the range to dial in the gas system. Pretty straight forward, I thought.
 
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I stick with SLR Sentry adjustable gas blocks and haven’t had any issues over several thousand rounds through my AR10. It's not rocket science.. open it up until the bolt locks back. AR10s are much more picky on parts and fitment. I've moved my JP SCS from the standard setting to H3 weight and it still cycled. What I found was that in the H2/H3 configurations it was smooth and easy on brass.

The only 2 issues I've seen could occur are:
1) AGB is not lined up with the gas port. Use a borescope to align the port with the AGB.. works 100%
2) Gas port is undersized.. this is unlikely but easily fixed by chucking a reamer into a drill and opening it up
 
I guess to me you use an adjustable gas block if your suppressed, or your that guy that doesn't know what buffer and gas length to use.
Sorry folks im not the person at the range who can't figure out why his rifle isn't functioning. I do have a rifle with a adj gas block and it doesn't work any better than the rifles i have that don't.
 
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Cr1775 said:
I guess to me you use an adjustable gas block if your suppressed, or your that guy that doesn't know what buffer and gas length to use.
Sorry folks im not the person at the range who can't figure out why his rifle isn't functioning. I do have a rifle with a adj gas block and it doesn't work any better than the rifles i have that don't.
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I believe you that your guns work. This is about fine tuning if you know what you're doing.
Since I'm always making car analogies, think of it like your air/fuel ratio. From the factory you might be a little rich. It offers a safety buffer, gives acceptable performance and gets people to work, which is what the vast majority of car owners want.
But every gearhead knows you can fine tune your A/F for more power or efficiency.
This isn't really the forum where people want to leave things stock and miss out on potential performance increases.
Fine tuning gas has multiple benefits from better brass life, parts life, lower recoil, potentially more reliability etc.
The guys you see that can't get their AGB's figured out are the same kind of guys blowing up perfectly good engines by "tuning" them. Don't blame the parts they are using for their incompetence.
 
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TonyTheTiger said:
I believe you that your guns work. This is about fine tuning if you know what you're doing.
Since I'm always making car analogies, think of it like your air/fuel ratio. From the factory you might be a little rich. It offers a safety buffer, gives acceptable performance and gets people to work, which is what the vast majority of car owners want.
But every gearhead knows you can fine tune your A/F for more power or efficiency.
This isn't really the forum where people want to leave things stock and miss out on potential performance increases.
Fine tuning gas has multiple benefits from better brass life, parts life, lower recoil, potentially more reliability etc.
The guys you see that can't get their AGB's figured out are the same kind of guys blowing up perfectly good engines by "tuning" them. Don't blame the parts they are using for their incompetence.
Click to expand...
No sarcasm here…
You win the post of the month award with this one…
 
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Yeah I'm pretty bent on diy. I feel I can build something pretty nice for a lot less than buying an LMT or KA. I guess we will see. Maybe I will just build a really cool looking paper weight, but I think I can do better than that. I am a logger so pretty inclined to tinker with shit (and break shit) until something works. As a friend of mine used to say "I'm just going to bang my head against the wall until something comes out".
 
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You absolutely can build it yourself. I have the same DIY issues. You'll hear many horror stories about building large frame gassers, but IMHO, if you put some thought into, and use some common sense, in your choice of parts, you'll probably end up with a dependable, accurate weapon. Will there be some issues to iron out? Probably. But with some studying of those issues, and posting questions on here, you'll learn that weapon inside and out.

I just built an 18" 308 a few months ago. Had some minor bugs to work out. Learned about the rifle with help from good folks on this site and my own research, and now have a weapon that runs, is accurate, and I have the pride of knowing I put it all together. I enjoy that shit. Some folks don't. That's alright. There's room here for all kinds.

Build that thing, and let us know how it runs. If it doesn't, ask. There are some very sharp, very helpful folks here that'll get you squared away. Happy wrenchin'.
 
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