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.
The barrel needs to be dimpled for those set screws. It’s really not a difficult operation and can be done by the end user. I can understand though if you want it professionally done to make sure it’s done cleanly.
Honestly, I’m quite surprised DD didn’t dimple the barrel when they installed the Syrac.
The dimples serve a larger purpose than indexing the block.
Check out the instructions Geissele includes with their GBs. Should provide some helpful info for you.
Dimpling at home is easy if you’re handy at all hand have a drill. I just take a pointy punch and make a small starting dimple so the drill bit doesn’t wander. Then I take a drill bit and start drilling away until the dimple is deep enough. Drilling on barrel steel goes pretty slow so it’s not very easy to go too deep.
Dimple the barrel. Use McMaster Carr knurled cup tip screws. Use Resbond 907TS blue or loctite high temp red threadlocker (271 IIRC). Enjoy your repeating rifle again.
To repeat- you can dimple the barrel yourself. All the dimple needs to be is a shallow drill start. Barrel steel isn’t very hard as steel goes, and it’s easy to go too deep.
Use blue Loktite on the screws and stake them lightly. You can use a light coating of Never Seez or green Loktite on the barrel itself to seal the gas block against leakage. If you use Loktite on the barrel, only use the green and make sure it’s made to wick
Some think that a free floated handguard will protect a gas block underneath against impacts. In fact a rail provides little protection against side impacts. A side impact against the rail will be transmitted to the projecting top of the gas block with very little diminution and of course this will tend to twist the block. If the block twists the plenum and the gas port can be misaligned.
In my mind, this is the most important reason for dimpling, to provide stronger resistance against twisting.
On second thought, there would also be a forward force from the pressure in the gas tube. If we take the max gas tube pressure as 2kpsi, and the i.d. of the gas tube as .125 (iirc), the the maximum forward force would be about 24 lbs.
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
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:
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).
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.
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.
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 ?
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.
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.
