Hunting Washington Forum

Equipment & Gear => Guns and Ammo => Topic started by: Fl0und3rz on April 12, 2017, 08:46:58 PM

Title: Adjustable Gas Blocks
Post by: Fl0und3rz on April 12, 2017, 08:46:58 PM: So I picked up a couple of adjustable gas blocks for a few rifles, and I am an adjustable gas block noob.

This one
https://www.odinworks.com/Tunable_Gas_Block_p/gb-tune-ss.htm

for a 16" Alexander Arms chambered grendel mid-length gas.

And this one
http://www.seekinsprecision.com/seekins-precision-low-profile-adjustable-gas-block-750-dia.html

For a 20" 1:8 rifle-length gas.

The first link has this vid on adjustment.

But my questions for the experts are: what should I be shooting for as far as a testing/adjusting regime to ensure reliability, proper recoil and ejection, loads to use? Any words of wisdom are appreciated.
Title: Adjustable Gas Blocks
Post by: DJ_Mack on April 12, 2017, 11:20:46 PM: You are aiming for enough pressure to cycle your bolt and for the bolt to lock back when the mag is empty. It's like shooting a pistol with a hand load that doesn't have enough powder and it stovepipes. If it is open all the way you get over gassed. Which means when you shoot a lot of rounds more gas will pour back into your face. But the real problem is a very firm and hard action that doesn't need to be there, which causes you to come off of target. If it isn't open enough you will not get full action and it will create jams. I hope this helps. Let me know if you need more detail.

So in short shoot one round at a time and keep opening the gas block until your bolt locks back. Once it does you are almost perfect. When it locks back open it a quarter of a turn more and you are perfectly tuned.

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Title: Re: Adjustable Gas Blocks
Post by: Fl0und3rz on April 13, 2017, 09:29:52 AM: Quote from: DJ_Mack on April 12, 2017, 11:20:46 PM
So in short shoot one round at a time and keep opening the gas block until your bolt locks back. Once it does you are almost perfect. When it locks back open it a quarter of a turn more and you are perfectly tuned.

This does help. Thank you.

As far as the .223/5.56, I plan on shooting all manner of loads from 55 grain to 77 grain. Would it be best to get it set for 55 grain, assuming that 62, 69, and 77 will cycle as well?

Of course I plan on testing it. At this point I am mostly trying to figure out what to take to the range to avoid multiple trips.
Title: Re: Adjustable Gas Blocks
Post by: aaronoto on April 13, 2017, 10:57:48 AM: In addition to bolt lock back on last round, watch your ejection pattern. A properly gassed gun should be ejecting brass between 3-4 o'clock (barrel being 12 o'clock).

I wouldn't run an adjustable gas block unless you're running a suppressor though, and even then I wouldn't run one unless it was a suppressed SBR. You can get reliable operation and ejection with 55-77g ammo with a standard carbine spring and an H or H2 buffer.
Title: Re: Adjustable Gas Blocks
Post by: Fl0und3rz on April 13, 2017, 11:07:46 AM: Thanks.

The 20" 1:8 AR is not going to be a suppressed SBR, and it is with an A2 stock. The problem with this particular rifle is that is known (from internet, my prior experience with exact same rifle, and prior owners experience with this rifle) to have cycling issues (short cycling, failure to lock back). I suspect gas block misplacement, given the configuration, so the block is coming off no matter, and a new handguard and gas block are going on.

The adjustable block seemed like an advisable way to go, and some people here are sworn on them, opposite of your advice (which is not taken without appreciation).
Title: Re: Adjustable Gas Blocks
Post by: huntandjeep on April 13, 2017, 05:21:53 PM: I just installed and dialed in the Seekins you linked yesterday , on my 16" suppressed barrel. Night and day difference from the old gas block to the new one. Seems like the recoil is alot more tame. Once I got the rifle dialed in to where the bolt would stay open after one round , I gave another 1/8 turn to the adjustment screw on the gas block and called it good.
Title: Re: Adjustable Gas Blocks
Post by: Fl0und3rz on April 13, 2017, 07:11:32 PM: Nice.