Gunsmithing Adjustable gas block

[esorensen]

I finally got around to working on the AR10T gas block. I found that the brass was launched about 20'+ on good days. The reciprocation was violent as well. I increased the reciprocating mass with the Tubb CWS, but still the brass was getting hammered. I also got the Tubb spring and it slowed things up a bit too, but brass was still being launched way far off.

I spoke with David at Armalite, and he said the lower s/n of the rifle indicated it had a large gas port. The rifle was designed to function cold, hot, dirty, crappy ammo etc.

I figured that the easiest option to fix this "gas problem" would be to tap into the gas system with a screw that would cut off a portion of the flow, but still lock back on an empty mag.

I milled a small flat on the block and drilled and tapped an 8-40 hole. A small set screw would be the regulator.

I shot it today with the laod that it likes. 43 gr. varget and 175 SMK's. I didn't really shoot for accuracy, just to see if it would work. It STILL locked back on the last round even with the screw all the way in! The brass however, is only about 5' away now. MUCH better! It only took about a half an hour to get this done too. The recoil is A LOT slower to boot. All in all, it was a great modification that I should have done a while ago.

 

[AKA-Spook]

Re: Adjustable gas block

Nice work!

 

[esorensen]

Re: Adjustable gas block

Thanks! Redneck gunsmithing at its finest! Maybe not gunsmithing, I don't want to pollute the term with the likes of myself. Maybe just plumber or pipefitter.

 

[skurtz]

Re: Adjustable gas block

From your picture it looks like you drilled thru the gas tube. Gas tubes have been have been known to break and stick in the carrier key making a ar10/15 a single shot after being drilled or modified.
I used a JP Enterprises adjustable gas block on my LR308 to get the same results. The screw is located between the gas port and the gas tube elminating the issue.

 

[Clark]

Re: Adjustable gas block

Thanks for posting that.

I built FALs 15 years ago that had adjustable gas.

I have fabricated BAR gas regulators to get the right adjustment.
I think is easier to just buy the part and ream them out.

I have been fantasizing an AR regulator.
The Blue Dot loads with light bullets will not cycle an AR15 with stock gas hole and springs. I was wondering if I could just use a screw.

 

[esorensen]

Re: Adjustable gas block

Yep, drilled right thru the gas tube. I couldn't find anyone who made a AR10 regulator that I liked or wasn't a million dollars, so I just fabbed it on my own. Thanks for the heads up on the tube failure. It still seemed quite strong after drilling it though. I am pretty sure the AR10 gas tubes are a bit larger than the AR15 counterparts, but I may be wrong.

 

[skurtz]

Re: Adjustable gas block

The gas tube on my DPMS .308 is the same as my ar15s.

You may not have any issues. Thought I would give you a heads up.

 

[Jumper]

Re: Adjustable gas block

I saw a similar thread over on another board where the same type of modification was made to a Mini 30. I remember that it was recommended to that guy to use a stainless steel screw since it is more resistant to heat. Nice work! I was thinking of doing something similar to my DPMS LR308 before I sold it.

 

[FCS]

Re: Adjustable gas block

Gas tube on an Armalite AR-10 is 0.250" longer than an AR-15.

Just an FYI.

 

[Hoser]

Re: Adjustable gas block

Very cool. If it doesent hold, let me know. I have an older JP adj gas block gathering dust.

Looks like I will see you at the March Sniper match. Bring 40 rounds.

If I cant use the I am flying excuse, neither can you.

 

[esorensen]

Re: Adjustable gas block

Thanks, Hoser. I just got the orange chopper back and already flyin' my ass off. People are just sicker than shit and busted up all over. Job security I guess.

The old gas tube has a siamesed hole in it, so if it gives out, it's trash. What is the diameter (ID)of the JP block and how much for it?

Need to do a little more fine tuning for loads though. I just got some 155 Bergers in and want to see how they run. I may have to do more surgery on the AR as it is pre-M4 feed ramps. VLDs may have a problem with nosing into the reciever.

 

[GUNNER75]

Re: Adjustable gas block

Who does manufacture adjustable gas blocks for the AR10T? Coming up with little on this end.

How has this performed for you?

I am asuming you only drilled through the first surface of the tube and not ALL the way through it correct?

 

[skurtz]

Re: Adjustable gas block

Try www.jprifles.com they have several that fit different barrel diameters. If you have questions call them up, they are very good about answering your questions.

 

[GUNNER75]

Re: Adjustable gas block

Should have mentioned that. They don't offer one with the .875 diameter. Nice guys for sure, and darn helpful, but no dice on the .875"