Gas Block and Barrel Dimpling

[MrRightWing]

I'm working on my first build and just realized that the barrel I ordered doesn't have dimples for the gas block (I have the YHM low profile gas block). Do I need to have my barrel dimpled or would it work just as well to use some loctite? I'm not too worried about not getting it lined up correctly the first time but I am worried about it moving after firing.

[MrRightWing]

Just realized this should be in the Technical Discussion. If a moderator sees this, would you kindly move it :)

[JasonM]

Dimpling for a set screw gas block is a very good idea.

[Hmac]

Dimpling for a set screw gas block is a very good idea.

And then having it drilled and pinned...

LocTite loosens under heat. Not the best choice for a gas block.

[RGoose]

I recommend sending the barrel and gas block off to ADCO or a similar service to have the gas block drilled for pins or dimpled at the very least.

[Hmac]

I've had barrel work done by ADCO, Rainier, and AR15Barrels. All three places did an excellent job. ADCO was the most expensive, Rainier was the most friendly and communicative, AR15Barrels was the cheapest. They all took about 2 weeks, IIRC.

Rainier, for example, wants $30 to pin a gas block, ADCO charges $55 for the same service. You'd have to email or call, but I'd bet that you could get your gas block dimpled, drilled, and pinned at Rainier or AR15Barrles for under $50. (ADCO wants $55 just for the pinning).

[fixit69]

Just my experience. I used low profile gas block on an upper with no dimpling, just loctite. The short version is, the gas block worked loose in a few rounds and turned my ar into a single shot.

Dimple it and or pin it.

[Dr Dues]

FWIW...

I've always wondered why the MK 12 has an exposed LPGB that is not pinned.

I prefer a pinned LPGB, but have two Factory BCM uppers w/ Free float rails...neither GB is pinned. BCM machines a substantial dimple in the barrel and when fixed, don't move.

One of the uppers has only 2-3 thousand rds through the tube and no issues thus far.....
The other upper, a 11.5" has about 6 thousand rds and has had no issues (the GB on this upper I used Rocksett on the set screws, and staked them...Because).

[jw0312]

Just my experience. I used low profile gas block on an upper with no dimpling, just loctite. The short version is, the gas block worked loose in a few rounds and turned my ar into a single shot.

Dimple it and or pin it.

I had a similar experience once. Loctite alone ain't enough!

[Hmac]

You guys are talking Loctite 266 Hi-Temp, right? Blue or red Loctite won't do anything given the heat involved. Or are you actually using "Loctite" as a generic "kleenex" label for Rocksett or similar high temperature threadlocker?

[MistWolf]

The gas block has to deal with lots of heat and not just high temperatures. Locktite is not a permanent thread locker.

If you're going to pin your gas block, set screws and dimpling are not needed

[Hmac]

If you're going to pin your gas block, set screws and dumpling are not needed

That's a good point, but I don't know if it's true or not. Dimpling is about a $10 gunsmithing service, even from an otherwise expensive place like ADCO. The barrels I've had pinned always came pre-dimpled so it's not something I've ever investigated.

[MrRightWing]

Thanks for the info. Looks like at the very least I should get it dimpled.

Edit: I found a local gunsmith that will dimple and pin it for $40. Is that a fair price?

[Hmac]

Edit: I found a local gunsmith that will dimple and pin it for $40. Is that a fair price?

If he has the right skills and appropriate jigs, it's as good as you'd get from Rainier, and significantly better if you take into account the cost of shipping and turnaround time. Pinning alone is $55 plus two-way shipping at ADCO.

[elephantrider]

If you are pinning your GB you do not neccessarily need to use a set screw, but here is my recomendation to do it anyway.

I've found the Vltor low profile gas blocks to be so tight that the set screw is just a little added insurance against coming loose.

A Centurion Arms low profile gas block, which is designed to be pinned, is looser. It has one threaded hole for a single set screw even though it is designed to be pinned. When the set screw is tightened it pulls the gas block tight against the gas port in the barrel. This potentially creates a little better gas seal around the port.

I would suspect that your YHM block will be on the looser side of things, so the set screw might help with the gas seal around the port in the barrel similar to a Centurion gas block.

[BC98]

I've used the barrel dimpling jig that Rainier Arms sells on two barrels with good success. I did rocksett both screws on the gas block in place and have had no issues. It may be another option.

[Merle]

I've used set screw gas blocks without dimpled barrels with no problem. Even with 30 round mag dumps there was never any loosening.

[Clint]

At the very least use Rocksett on the set screws.

I feel it works much better than loctite in this application.

A dimple is better.

A pin is best.

[Hmac]

I wouldn't use a pair of set screws on a round barrel on a rifle that had any kind of important function. The potential for failure is just too great. No quality manufacturer would sell a rifle set up that way.

[AR15barrels]

I recommend a single dimple and installation with rocksett as my standard means of assembling a sets few attached gas block to a barrel.
When people want a cross pin as well, I still drill a detent and set a setscrew into the detent to hold the gas block in place while I cross drill the gas block and barrel as a mated pair.

[MrRightWing]

My gunsmith drilled two set screw dimples for me for free! Think I'll go with that. Thanks for all input! Great info from this forum, as usual!

[jjslice]

Tighten the set screws onto the barrel. Mark where you need to drill by where the set screws left a mark and drill with a bit so there's enough for the set screw to sit into. Not that difficult