Gunsmithing Lining up the gas block

[Shooting Impulse]

Hey guys! An easy question, I'm sure but a question non-the-less.
How do you line up a gas block that is not pinned in place? I'm using a MI low profile gas block that is secured with screws. What is a good method to ensure all the gas holes are lined up?
Thank you in advance for your help!!
-Chris

 

[HPLLC]

Re: Lining up the gas block

Flip the block upside down- take the allen screw out (you'll notice the gas hole is drilled through one of the allen holes, and center the allen hole on the gas port hole. You'll notice that that leaves the gas block about 1/32" from the shoulder on the barrel. That's because they are made to be compatible with handguard retainers.

Well you probably won't be using one, but need to account for that space. Tighten the other set screw till it secures the block with the hole centered over the gas port. Now take some tape and loop it around the barrel to where it meets the block. That way when you flip the whole mess over you can touch the tape and know your front rear alignment is good.

flip the barrel over and dead center of the top of the gas block put a piece of tape lengthwise on the barrel as a witness mark for the hole recess location.

Now flip the gas block over, touch the tape for front rear alignment, allign the hole center axially with the tape running lengthwise, tighten one screw and dot the center of the hole with a sharpy, or tap it with a center punch.

Now put the other screw in, and remove the first so you can dot/or center punch the other hole if you want. Now remove the block, drill the recesses, and install the block with thread locker on the threads.

Done. Now you can install a gas tube, plug the barrel and blow to test gas flows through the port and tube.

How would a machinist do it? He would use a collet block to fixture the hole straight up- touching his (gas port size) drill bit dead center, set a vise stop, raise the quill, change drill bits, and flip the block over, touch off the vise stop, and sink the recess with a center drill, then use the horizontal way to move the required dimension to drill the other recess, but that's with a Bridgeport ($3500-$5500 used) and a collet block, vise and a shop. It's the right way, but it costs $5500 plus overhead for the shop. Trust me the tape will work, and it's the way to do it for $100 in your home with a drill press.

 

[Phylodog]

Re: Lining up the gas block

Low pro gas blocks are designed to be installed with a handguard retaining ring? I just built an upper and used a retaining ring and low pro gas block for the first time. The gas ports didn't align properly due to the retaining ring forcing the gas block away from the barrel shoulder. You could see the evidence when I removed the gas block after test firing. The rifle cycled fine but would not lock back on an empty mag. That gas block is at my smith's getting decked off the thickness of the retaining ring to bring things back into alignment.

I'm asking here, as I really don't know if there is a standard approach for those manufacturing the gas blocks. I've installed a dozen low pro gas blocks up against the barrel shoulder and they all ran great without a retaining ring on there.

 

[FNARSHOOTER]

Re: Lining up the gas block

I have found blocks that line up pushed all the way back and those that need to be spaced for a retaining ring. Sometimes its the barrel that is the deciding factor. Some blocks have a oval port to be used either way and on top of that all some gastubes don't line up and partly block the passage.Add to that undersized ports in the barrels and it's a nightmare.The answer is MEASURE EVERYTHING do the math and line up and fit the parts. If you can't do the math or don't have the tools. Take it to a pro BEFORE you screw it up ,much cheaper than after.

 

[LoneWolfUSMC]

Re: Lining up the gas block

Depends on the block.

The MI block I just installed on a 20" HABR was designed to be used without the cap.

To be sure I use the "depth" measuring function on a set of calipers and measure the port distance from the back of the block. I then compare this with the distance of the barrel port from the shoulder. generally the hole in the gas block is over sized or slotted, so a little misalignment is not the end of the world, however I like to get it as close as possible.

 

[Shooting Impulse]

Re: Lining up the gas block

Thanks for all the feedback! This helps alot.

 

[Phylodog]

Re: Lining up the gas block

This was the first I've ever installed with a cap and they've all lined up perfectly without. That's why I was asking about gas blocks being designed to work with a retaining ring/cap. Hasn't been my experience.