Non-dimpled Barrel and Set Screw Adj Gas Block Install - Advise

[BufordTJustice]

I too was curious about a torque spec. After not finding anything I settled on 30-35in-lbs and red 272 loctite after dimpling only the rear set screw location. Clint at Black River Tactical and BCM recomended to just do the rear dimple. Not all gas blocks have the same distance to center between screws, btw. Check out BRD engineering for a dimple jig

Yep. I dimpled both on one barrel and things got interesting when a new gas block did NOT line up with the front screw dimple.

[lysander]

Yes, I have searched and found some good information but would like some additional advise about install of an adjustable gas block on my DD MK18 please.

Won't get into all the gory details but a Syrac adjustable gas block was installed by DD for me as part of a warranty repair agreement for a problem child MK18 I have had fits with since day one (for the record, though frustrating, DD has bent over backwards to help me and their warranty administrator has been nothing short of outstanding). I run the upper dedicated suppressed. Well, after just a couple hundred rounds after warranty repair, the upper become a single shot out of the blue yesterday. The problem? The gas block had come loose and was sliding down the barrel cutting off the gas. Here's my setup:

DD MK18 10.3 barrel
Syrac Gen II adjustable gas block - set screws
Dedicated suppressed upper - running a GemTech Trek Titanium
Apparently DD does not dimple their barrels. Found that out last night upon tear down of the upper. Further, it does not appear the block was installed using any thread locker/Loctite.

After my research, it appears as though dimpling isn't critical and resetting the block with degreased threads and red Loctite on the set screws should work.

Is there a torque spec I should use for the set screws? Is very hand tight with the red Loctite sufficient?

Long run, is just best to have the barrel dimpled? Seems the main purpose of dimples is simply timing of the block. There are clear marks on the barrel from the previous install I can repeat without the dimples.

If it is recommended I get the barrel dimpled, any recommendations on a gunsmith? We have nobody around here who can do it. I have asked. I will need to have this sent out for smithing. Pain in the arse.

Any other advice/recommendations? First time with this. Thanks.

You can get away without dimpling, but why risk it?

Depending on the size set screw you are working with the axial clamping force is fairly high, I'll leave to others to decide if they are high enough. Below is the recommended maximum torque (in-lbs) and maximum available axial clamping force (lbs, the maximum force necessary to slide the collar along the shaft while held by one set screw) for three common size set screws:

Alloy steel screw and collar
Screw size // torque // maximum axial clamping force
8-32 // 20 // 375
10-32 // 35 // 550
1/4 - 20 // 90 // 950

Stainless steel screw and collar
Screw size // torque // maximum axial clamping force
8-32 // 15 // 200
10-32 // 25 // 300
1/4 - 20 // 70 // 550

EDIT: This is based on a quality ASME B18.3 cup point set screw.
EDIT #2: The use of 2 set screws will not give you twice the clamp load, the fastener closest to the load will always bear most of the load. In this case the screw closest to the gas block shoulder (the one you should dimple).

[arptsprt]

Good information and advise, as usual. Thanks everyone.

I am going to dimple the barrel myself this week. Rear dimple only. I'll have to contact Syrac Ordinance for the spec on their set screws.

[Joe Mamma]

Good information and advise, as usual. Thanks everyone.

I am going to dimple the barrel myself this week. Rear dimple only. I'll have to contact Syrac Ordinance for the spec on their set screws.

The set screws are 10-32 thread and 3/32 hex head. I'm guessing that they are probably 316 stainless steel, but let me know if I am wrong on the material.

One thing Syrac will probably not volunteer is the fact that their adjustment screws can seize up pretty easily (just getting carbon fouled from regular use). My suggestion is to put a drop of CLP on it and make sure you move the screw back and forth every couple of hundred rounds or so.

Joe Mamma

[Laust]

I too was curious about a torque spec. After not finding anything I settled on 30-35in-lbs and red 272 loctite after dimpling only the rear set screw location. Clint at Black River Tactical and BCM recomended to just do the rear dimple. Not all gas blocks have the same distance to center between screws, btw. Check out BRD engineering for a dimple jig

For everyone that builds, this place is excellent.

[arptsprt]

You are correct on the material.

Funny about the adjustment screw comment. I had read that and my initial thought was a stuck adjustment screw as the culprit. It was as I was playing around with adjustment screw when I noticed the movement on the entire gas block itself. I will certainly be aware to lube as you recommend - in fact it already got a treatment of Fireclean.

The set screws are 10-32 thread and 3/32 hex head. I'm guessing that they are probably 316 stainless steel, but let me know if I am wrong on the material.

One thing Syrac will probably not volunteer is the fact that their adjustment screws can seize up pretty easily (just getting carbon fouled from regular use). My suggestion is to put a drop of CLP on it and make sure you move the screw back and forth every couple of hundred rounds or so.

Joe Mamma

[BufordTJustice]

For everyone that builds, this place is excellent.

Yep. Clint is good people and might know a little thing or two about the AR platform.

Seriously, his stuff is made to exacting specifications and is VERY reasonably priced.

[Blak1508]

As you guys had just stated, I just ran into the situation on a barrel where I had a installed Geissele Nitride Super Gas Block with just the set screws on a BCM BFH barrel. I have gone back and forth about dimpling the GB. Recently I started shooting suppressed so I deinstalled the GSGB and I installed a set screw SRL adjustable GB and I noticed that the holes for the set screws did not line up at all from where the holes on the Geissele were anchored, the Geissele holes appeared to be closer together in reference to the GB while the SLR's were wider apart. What if I had dimpled the first GB? Does this compromise the exterior of the barrel assumed I had dimpled the Geissele block? As in would I have an issue dimpling another GB ?

[Clint]

That's why we recommend dimpling only the rear set screw.

This rear set screw is always directly opposite the gas port on all gas blocks, so any block will line up on a barrel with one dimple.

A shallow dimple will not compromise the integrity of the barrel and significantly increases the holding power of the set screw, especially if the set screw is the knurled type that we supply with our gas blocks.

As you guys had just stated, I just ran into the situation on a barrel where I had a installed Geissele Nitride Super Gas Block with just the set screws on a BCM BFH barrel. I have gone back and forth about dimpling the GB. Recently I started shooting suppressed so I deinstalled the GSGB and I installed a set screw SRL adjustable GB and I noticed that the holes for the set screws did not line up at all from where the holes on the Geissele were anchored, the Geissele holes appeared to be closer together in reference to the GB while the SLR's were wider apart. What if I had dimpled the first GB? Does this compromise the exterior of the barrel assumed I had dimpled the Geissele block? As in would I have an issue dimpling another GB ?

[Blak1508]

Thank you for the Info Sir, I usually dimple my GB but on that exact build I had not in anticipation that I would be moving to an adjustable. In the future I will always dimple the rear set at the very least. Once again I appreciate it.