I’m putting a build list together for a 308 and I see a lot of people putting adjustable gas blocks in their builds. Some say it is to minimize felt recoil, some say it is to fine tune that amount of gas that the gun operates on. My question is, is an adjustable gas block a must have for a 308? I don’t care about the recoil, I’m more concerned with under/over gas issues.
If I was to build again or another upper, without a doubt I would use another adjustable GB. Specifically the Syrac based on fit, finish, ease of use and rigidity when installed.
Use of the adj GB takes any guess work or gas port issues out of the equation.
A buddy built an LR-308 that was over gassed. It was beating up the brass pretty bad. An adjustable gas block made it much more fun to shoot and the extractor isn’t trying to rip the butt off the casings. I put one on my LR-243 and found out that I really didn’t need it. Alot just depends on your barrel gas port, length of the gas system and how hot of rounds you are running in it.
If you you have another gas block, I would suggest giving it a try before you spend another $100 on a block you may not need.
An adjustable gas block is a must have with any platform/caliber. With the wide range of gas ports (in and out of spec) and ammo it just makes sense.
There’s only so much you can adjust with springs and weights - if you have a wildly over gassed barrel that’s the only way to tame it.
Why anyone would refuse the ability to adjust the one factor that controls the function of the gun - at a mere extra $50 or so is beyond me.
Some people feel that more moving parts, more sources of failure. Adjustable gas blocks have been known to give out for one reason or another.
If you have a over-gassed problem, an adjustable block will fix it. If you don’t have a problem, you don’t have a problem…
Fwiw-most barrels are overgased. They have to be in order to function reliably with every type of ammo.
Unless they are set up for a particular ammo/pressure.
Very few are.
I only know of one-which doesnt mean there arent more.
If you ever plan on suppressing it, an adjustable gas block will allow you to turn the gas down with the can on. I am looking at getting a DPMS GII in the near future, and i’ll be getting an adjustable gas block for shooting suppressed.
Thanks for the input everybody. As of right now, I have no intentions of suppressing it. It will primarily be a long(ish) range gun with some coyote hunting mixed in there. I’m leaning towards the adjustable gas block.
I just tore my DMR down for a cerakote job. I had a Wilson Combat adjustable gas block, which unquestionably is the WORST gas block in the known universe… So I came here a lookin’ for an answer to the question: “Should I stick with an adjustable gas block on my DMR, 308 w/ 18” barrel, which will most often run an SDN-6?" (Obviously not a Wilson Combat)
I have an SLR S7 on my 11.5 and SPR. I’m thinking yes. Does anyone have any other thoughts on this since the was posted 2 years ago?
I’m thinking an adjustable gas block is a good preventative measure.
I know the SLR Sentry 7, I also have seen a Superlative Arms on Rainier Arms with very good reviews…
Thoughts - Any other thoughts on the matter in the two years since this was originally posted?
My thought is yes, use the adj. gas block on your .308.
Either the SLR or SA’s have worked for me and are good kit.
The .308 ARs seem a bit more issue prone than their 5.56 counterparts in my experience.
The ability to fine tune the gas system I see as an advantage with .308.
Just keep in mind, if the gas port is the right size, an adjustable gas block is useless
Absolutely yes. The greater gas volume of the 308 class cartridges makes it necessary because one port size for suppressed will be undergassed for without and the right one for without will be way overgassed. 5.56 you can get away with fixed.
That’s the $50,000 question. Mist… is my BA the correct port size for my application. I tend to agree. I see gaijin’s point, the 308 platform, DPMS variant in particular doesn’t really have a seat at the “table of mil spec standards” like it’s big little bro AR-15.
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Mine with an 18" BA Modern Series Government profile is definitely not over gassed with an Aero gas block. With an Aero carbine buffer and Tubbs spring, the carrier speed with foreign M80-type ammo is actually a bit slow. It works great with my handloads and 168 gr FGGM.
The only way to tell is to shoot the rifle. I haven’t had the funds to fully explore tuning my M&P-10, but it short strokes on NATO spec ammo in the winter and runs fine on commercial spec ammo. Someday, I’m gonna have to gather up a variety of buffers and go see what happens.
We can talk all day about saving money by getting the right parts from the start, but without actual testing and keeping notes, we’ll never know which parts are right and testing costs time and money
Rifle or midlength gas system?
What is the port size now?
Mine has a mid length gas system. I didn’t measure the port.
I get no failures with '80 Hirt and '16 MEN. When using a Magpul LR 10 round mag, the last round sometimes doesn’t make it through the ejection port.
I’ve shoot a wide variety of ammo. From - - - Federal 175gr SMK OTM
- Federal 168 OTM
- TulAmmo steel case,
- ZQi 7.62x51 147gr,
- MEN 147gr MEN
- Prefect 150gr
The one ammo I had issues with was Hirtenberger 147gr. FMJ. I experienced several FTF, I’m got very hard firing pin strikes on the Bergen primer, but no bang. No other ammo has caused me problems before. Some of the ammo fired fine, some didn’t.
I haven’t put a can on my .308 because it’s still hostage, but the weapon cycles perfectly with all that ammo. Exception noted.
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18" rifle gas. Port size? No idea. I’ll email Kyle and ask him.
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