Adjustable Gas Block on SFAR?

[KneverKnew]

I've installed an aero precision adjustable gas block on my 20" SFAR. now I'm wondering if I should tune it with the standard 3oz buffer that came with it or continue using the H3 or H3 buffer?

Please share your thoughts.

 

[Mobuck]

I'd try it with the 3 oz and if that doesn't function properly, change to the H3.
Part of this process depends on what your intended use may be and how much you intend to use the rifle.
I have AR's that are quite obviously 'over gassed' BUT they're hunting rifles that only fire 10-20 rounds per year. I feel it's acceptable to do this as the limited use is not going to beat the gun up that much and the unquestionable function is good.
This is also why mil-spec carbines are over gassed--to ensure absolute function regardless of environment or contamination. A certain level of 'self destruction' is acceptable.
A 'range rifle' that's fired hundreds or thousands of times per year in an informal (non competitive) range setting can be tuned to a 'softer' level of function.
Some 'new' rifles just demand more break in than others. I gave Grandson an AR upper for Christmas. He expected it to work perfectly from the box. It seems to be stubborn and fails to lock open on an empty mag about 40-50%. He complained until I replaced the upper with another. The fact that this upper was shooting great and he really shouldn't be concerned about the problem was lost on him. I'm shooting that upper as a test bed for reloads and it's doing great. I DON'T CARE that it hasn't worked itself out but I'm confident it will eventually.

 

[KneverKnew]

Thanks for your input Mobuck. My plans line up with your suggestion. Right now I am doing a deep dive cleaning of the SFAR to have a clean start, so to speak, to run the aero AGB through its paces. I hope to get to the range early this coming week.

 

[Mike 8939]

I agree with you. It's a matter of overgassing causing to fast timing. Had similar issues with my 458 Socom. I'm sure the H3 should help. I'm thinking adding a flat wound spring might be necessary too but testing will tell.
And why not use a silencer in a 308?
Yes, #1 setting is for cans.

Geissele has a spring that will not take a set as quick as others watch there youtube video on this to explain the new spring and the test machine they I house built to TEST this

 

[KneverKnew]

Range results with the SFAR using Aero Precision AGB. I tested with Austrian 7.62 (STG-58.)
I used a standard carbine spring and 3oz buffer.
After adjusting Aero AGB I got 3:00-4:00 ejection pattern with 6'-8' ejection. I got pretty consistent lock back on empty depending on magazine used. Still trying to figure out the magazine issues.
The bad double ejector case head swipes/ gouges were now reduced to a couple a small shiny spots but no raised gouges/ raised metal.
I also tried the H3 buffer and seemed to work fine as well. Need to try different buffer/spring combinations. When I swapped the long spring in place of standard spring the bolt would not lock back. More testing needed.
I will next test various factory 308 loads as well as some of my good reloads with 168 HPBT's.

 

[Mobuck]

"When I swapped the long spring in place of standard spring the bolt would not lock back."
This usually means the compressed spring is too long stopping rearward travel of the BCG before full travel. This is not the way the system is supposed to work.
If the H3 buffer is allowing the bolt to reach full travel and function, I'd use it vs the 3 oz. I like to see AR's tossing brass at around 4:00 and 6-8' seems excessive.
We have and use AR's that eject at 2-3 o'clock when used suppressed but keep in mind these are hunting guns and often fire less than 10 rounds per year in suppressed mode. We also have 'suppressor tuned' AR's that eject at 4-5 o'clock when fired w/o the device. These may fail to lock open on an empty mag but this is not an issue outside the realm of FTF combat.

 

[KneverKnew]

Gee, I though getting it down to 6'-8' from 10'-12' was doing good.
I will continue my adjustment tests.

 

[Mobuck]

No kidding? The typical AR 15 .223 should drop brass within 3-4' when fired from the bench and a bit more firing off-hand. My 'adjusted for low noise' AR's drop cases on the edge of the 4' wide shooting table or just off the edge.

 

[KneverKnew]

I understand the 3'-4' for a 5.56 but does that same rule apply to 308?

 

[Mobuck]

No idea because I have not even seen one in person let alone fired one. Some 'ideas' just aren't as great as hoped for.