Gas Block Set Screw Torque [Archive]

prepare

04-11-20, 06:19

Is there a torque spec for gas block set screws?

jsbhike

04-11-20, 08:48

Barring specific instructions from the gas block company there are guides like this.

https://www.aftfasteners.com/socket-set-screws-dimensions-mechanical-properties/

prepare

04-11-20, 08:57

I don't recall ever seeing a manufactures torque spec for GB set screws.

bamashooter

04-12-20, 15:15

I've seen them expressed from 20-30 inch pounds. I always just tighten the crap out of them knowing I could probably go another 1/8th turn or so if the tool or item didn't snap.

prepare

04-12-20, 16:40

Being as though LPGB's aren't mil-spec there is no mil torque specification.

titsonritz

04-14-20, 22:50

I use the German spec, gutentight

Leonidas24

04-15-20, 02:51

I recall a study done a few years ago in which the torque on the gas block screws was proportional to deformation of the bore. The more a screw was tightened whether it was into a dimple or not resulted in measurable strain in the steel of the barrel that affected accuracy. If I can find the article I'll post it.

Otherwise 20-25 in-lbs with a drop of red loctite on each screw and I've never had one back out on any of my guns or customers' guns.

prepare

04-15-20, 03:59

I recall a study done a few years ago in which the torque on the gas block screws was proportional to deformation of the bore. The more a screw was tightened whether it was into a dimple or not resulted in measurable strain in the steel of the barrel that affected accuracy. If I can find the article I'll post it.

Otherwise 20-25 in-lbs with a drop of red loctite on each screw and I've never had one back out on any of my guns or customers' guns.

I would definitely be interested in that study and who conducted it.

WS6

04-15-20, 05:42

Bore deformation is a thing, if minute. If it's on a "work gun", I'd say 25 in-lb and rocksett. If it's on a "accuracy first, last, always" gun, I'd say 10 in-lb and rocksett, with witness mark in a location you can easily check it.

prepare

04-15-20, 07:03

The LPGB is one of the few components that there's no TDP for. Perhaps the study that Leonidas24 mentioned above contains some actual testing data.

Leonidas24

04-15-20, 11:14

Set Screw Gas Block Internal Deflection (https://www.m4carbine.net/showthread.php?172573-Set-Screw-Gas-Block-Internal-Deflection)

So it wasn't a scientific study per se; one of the members here ran an FEA simulation plugging in numbers and force exertions through a medium and reported the results. Bore deflection measured .00001-.00003". Other info I found was primarily from the 6mmAR forums and most of the guys there refuse to use set screw gas blocks. Keep in mind these guys are printing 1/4" MOA groups and every variable is being accounted for.

OP: Get a FAT Wrench from Wheeler if you don't have one already. Well worth the investment. Set it to 20 in-lbs and secure your screws with red loctite. If you're still concerned with them backing out then 2 minutes with a center punch to stake the screws will take care of any concerns.

edit: https://www.engineersedge.com/torque_table_sae.htm

bruin

04-15-20, 11:21

I use the German spec, gutentightAs I learned from IG, this.

I have experienced a LPGB sliding up because the screws loosened, with the barrel dimpled and red loctite. Insufficient screw torque (mea culpa), around 15 in-lbs IIRC. Now I get them as tight as I can hand holding the short leg of an Allen key.

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