I've got several barrels with various gas blocks I'd like to pin.  Since jigs to do this are pretty expensive, and I have several different types to do, I figured I'd 3D print my own for a few bucks.  A simple chunk of plastic fitted to the correct gas block size with a metal bushing to keep the drill bit lined up should do the trick.

Picture just for reference.  I still need to figure out what size hole to be drilling, and the green chunk of plastic will probably be tweaked for print-ability.

Attached File


Then I can secure it in a vise and use a hand drill, or drill press.

My question is, where should a be drilling?  Is there a rule of thumb as to how deep into the barrel you should go?  I'd imagine staying as far away from the bore as possible is best both for safety and minimizing accuracy problems.

Nice CAD


I'm guessing About 1/3 to 1/2  of the pin diameter. Most coil pins are 1/8"OD    1/3 of 1/8" = 1/24"

Some are now lowering the cutout so less barrel material needs to be removed. Less is more in this case.

You only need enough to lock it in from rotation and from moving fore and aft.

https://blackrivertactical.com/WP/BRT-MicroPin-Gas-Block-750-p17534540

If you could make an adj. in the jig for cut depth that would be sweet.



Accuracy with a 16" barrel having a pinned GB.

Thanks!

Ordered some 1/8" OD x 1/2" long coil spring pins, and a #31 size drill bushing from Grainger.

Did some more looking, and most out there seem to be like you say, 1/2 to maybe a little less the diameter of the pin.  I may just do 1/3 and call it good.

Dunno if I'll make the jig adjustable.  A little hard to do with plastic and keep the necessary rigidity.  

That whole cad drawing above took about 5 minutes, and changing hole position is trivial.  Could just make several STL files with different spacings.  Won't take much plastic to make one, you could print out a bunch of them all at once for very little money.

What do you hope to accomplish with these?

Hold the gas block on?  

I've seen some gas blocks that use them, and the specs say they're stronger than standard roll pins.

Also, it was cheaper for a 25 pack of them vs a 100 pack of standard roll pins (Grainger doesn't sell the standard stuff in packs less than 100).  Since 25 is probably more than I'll ever need to use, the stronger cheaper option is what I chose.

If you want the gas block to be rock solid you should use solid tapered pins.  Coil pins and split roll pins aren't going to be as effective.  Set screws and a dimple would to just as well.

This is for low profile gas blocks like in the picture and have limited room.  Some of which may be adjustable (could need to be field serviced).   A tapered pin would still probably be stronger, but would be less useful if you need to get a gas block apart away from a full shop.  Also, being low profile, they're protected under the handguard, don't have much leverage worries compared to a FSB, and don't have bayo lugs.

Also, all of the blocks in question already have set screws and dimpled barrels, which only leaves room for a single pin.  Since that's all the room I have, and for the reasons above, I think a coiled roll pin will serve very well as a backup holding device.

Suppose I could use a tapered pin on the non adjustable low pro blocks.  Wonder how much of an advantage tapered pins have on really skinny low pro blocks though.  They get most of their holding strength from the amount of surface area they contact, which will be a lot less on a low pro compared to a FSB.

I wouldn't even bother pinning a GB that is under a handguard.

^ This. The least amount necessary to secure the gas block. Anything you do to the barrel can distort the bore, so the less invasive the better. Criterion has measured bore deformation caused by set screw gas blocks via air gauging. A taper pin would likely cause much more deformation of the bore considering it is a wedge against the gas block and barrel. AK's have used straight pins of appropriate size to mount multiple barrel components (fsb,rsb and gb) for decades without issue, no need for taper.





BA uses coiled straight pins, no taper. Just so there is no confusion.

I would get rid of that protrusion and get the bushing closer to the gb. The shorter the drill bit, the less chance of deflection.

And they won't keep a GB from rotating.  Topic has been discussed several time on arfcom

That may or may not be the case but, one thing is for sure..Accuracy of a straight pinned barrel can not be used to determine the accuracy potential of a taper pinned barrel which is subjected to varying degrees of wedged tension against the bore.

Yeah, it will be more compact when I get the drill bushing and have actual dimensions.  The bushing is only an inch long, and I'll probably take a grinder to it to match the profile of the gasblock.  That'l give me metal all the way down, and should keep things from moving.