why adjustable gas block on 308 rifle

I have a MGI adjustable gas tube on a 223 AR and it seems to make very little different.

Would a gas block or other adjustable gas system do more in a 308 AR to reduce recoil?

I only have empirical data on this one, but an adjustable gas block has made incredible difference in several builds.

Here is a typical thread and there are numerous others (not about recoil specifically)...
http://www.ar15.com/forums/t_3_121/569850_New_CMMG_MK3_w__Issues___Ejection_Issues___Overgassing_Problem__Help_Appreciated_.html

Heavier buffers, springs made little difference to the 308s compared to a good adjustable gas block as far as recoil.

And yes, it has made little difference on AR15 builds for recoil or other problems (except with can).

My experience is the same as PCA's.

My AR10 was over gassed, using an adjustable gas block made it run much smother/less recoil and eliminated some FTF I was having.

I also have one on my 300 Whisper with pistol length gas system. This allows me to run sub-sonics as light as 150 grains and all super sonic loads with just a simple adjustment to the gas block.

My issue wasn't one of recoil reduction - it was all about the functionality/reliability. I did a LOT of research in multiple places about this when I was having issues and the same problem (and solution) kept coming up over and over again - overgassing. It appears that even if you aren't exhibiting serious issues, your rifle may still be overgassed. For whatever reason, this just seems to be a fairly common issue with many of the 308 AR-Type rifles. Remember, the FAL also incorporates an adjustable gas system as a matter of design (yes, I know it's a completely different op system).

I don't know if it's the cartridge, the manufacturing tolerances, the scaled-up size of the system or a combination of all of the above but there is a reason why heavy buffers, increased-power springs, washers/quarters, and adjustable gas blocks are selling as well as they are for .308's.

At the end of the day, it completely alleviated the issues I was having and I now have the flexibility to tune the rifle to different ammunition types if I choose.

YMMV, yada-yada...

May I ask which barrels you 3 are using? I believe the barrel manufacturer makes a difference (i.e. gas port diameter).

I've got a Noveske 16" BBL and I don't believe it's "overgassed" per se - recoil is managable and I've never had a single feeding issue.

I've never used lower power mil 7.62 either though - it's all been full power 308.

I'm in the process of moving to the VLTOR A5 sytem (A5 6-pos AR10 tube, H3 or heavier AR15 carbine buffer and an AR10 rifle spring.) This is mainly to smooth out the action and the fact that an AR15 collapsable carbine-length system doesn't allow much forgiveness on a 308 action.

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This is so true as I have seen many barrels of many brands and it seems the port sizes differ.
When you purchase one of the top of the line barrels chances are the maker did some home work
on port sizes and position of the port and that is some of the reasons they are top a the line barrels and cost more.

Exactly - Noveske puts in extensive R&D on each barrel they sell. Profile, weight, gas port size, etc. A LOT of work goes into finding the ideal gas port diameter.

I find their barrels shoot the softest out of anybody's, yet are still 100% reliable.

I agree with the comments on having some R&D going into the port size but no matter what design is used it is a compromise. One size does not work best for all loads or with/without a silencer. Having an adjustable block you can select "the size" that is optimum for the load.

And that is why I made a adjustable gas block for my 308
.

Me too!

Does anybody have or know of a list of adjustable gas blocks and their various attributes? Lots of them seem to be custom pieces from what I've seen on the interwebs.

While not an exhaustive list, the ones I see referenced most often are the ones from JPE and PRI:

JP Enterprises
http://www.jprifles.com/1.4.6_gs.php


PRI
http://www.precisionreflex.com/Control_Brake_pr-4274.aspx?CAT=4274


I was originally going to go with a JPE low-profile .750 but Midway ran out literally as I was checking out so I went with the PRI based on the solid reviews. Great piece - well made, easy to install, and it does the job.

I got the JP because my stock DPMS was a little over-gassed. It n ow lays all the brass in one neat little pile and the recoil is noticeably lees. My only complaint is that is does not line up with the DPMS rail, but I can live with that. I am using a scope on it . Besides the chance of me having the talent to make one, well that won't happen

SLICK. Hows it work?

It's basically a needle valve with 12 dent positions per turn, one full turn is about 100% open. When used on my AR10 with standard 150 gr loads I get full function with it about half way open. When set to closed it is completely closed.
I used 17-4 stainless for the construction.

As others have said, puts the brass in a neat pile a few feet away with noticeably less/smother recoil.

Building something similar here

Those of you running adjustable blocks, are you using loctite on the adjustment screw? I'm considering getting one but do not want to have to loctite the screw & then have to adjust it for different types of ammo.

However, this one from JP does look nice & would solve that problem..

There are adjustable gas blocks with a locking detent. No loktite needed.

I replied to your email but the short versions is "yes" - I used a small drop of the Blue (removable) Loc-Tite on the adjustment screw. It probably would have been fine but I wanted to snug it up a bit and make sure everything stays put. The beauty of the "blue" is that it doesn't set up as tightly and I can still adjust the screw without any excessive force.

Hopefully that helps - good luck with your rifle!

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