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Set Screw or Clamp on?

hewlett260

Sergeant
Full Member
Minuteman
Feb 19, 2011
513
3
35
California (Hell)
Looking to get a low profile Gas Block. I have a carbine length gas system and the hand-guard is a Samson Evolution rail 9 Ex. Because the rail goes over the Gas-Block, I don't really need an adjustable one. Looking to see what the benefits and shortcomings of each set screw vs. clamp on is. Any input helps.
 
Set screw is easy to line up and install if your barrel is dimpled for the set screws (usually just one dimple). It is the weakest method of securing a gas block. They are usually tied with pinned GBs for smallest size.

Clamping is much stronger - not quite as good as pinned, but VLTOR demonstrated a couple years ago that their clamping gas block wouldn't slip til over 100ft-lbs, and the barrel started slipping at the receiver before that point. You have to manually align them, but it's not a big deal. They tend to be a bit larger and won't fit under the smallest diameter rails, like a Troy TRX-Extreme or Alpha.
 
The only way I would go the set screw route is if I planned on drilling and pinning it. If you don't want to bother with that a good clamp on works great. If you are concerned about the screws loosening you can always stake them.

Sent from my Galaxy S3 using Tapatalk 2.
 
Clamp GB's won't fit in all free float rails. Not sure about the rail your using. As far as strength goes, I don't really have issues running set screw gas blocks (especially if the barrel is dimpled) since the block is covered by the handguard anyways. If your handguard is smashed so hard that it hits your gas block enough to twist it, you've probably got bigger things to worry about.
 
I have run both without issues. I prefer a set screw though, with a dimpled barrel. Less chance of slip and lower profile to fit under more rails.
 
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I have run both without issues. I prefer a set screw though, with a dimpled <strike>rail</strike>barrel. Less chance of slip and lower profile to fit under more rails.

+1 (assumed you meant dimpled barrel... That's the only way I'd go.
 
Just make sure you use a steel gas block on CLGS & MLGS guns. You can also red loc-tite the gas block in place, which will also help with the seal and accuracy. This is a common technique used by hi-power shooters and accuracy freaks.

I also found that in addition to the smaller ID handguards like the Troy TRX Extreme, the MI Lo-pro SS Gen II also will not fit over certain clamp-on gas blocks.
 
I have read that the clamp ons supposedly effect accuracy less that the set screw versions. I don't really know it that is correct or not. Can anybody confirm?
 
I have read that the clamp ons supposedly effect accuracy less that the set screw versions. I don't really know it that is correct or not. Can anybody confirm?

The thinking is that a clamp-on applies more even pressure circumferentially, while a set screw applies vertical pressure, pulling the bottom away from the journal, with tension on the screw.

With a dimpled barrel, the set screw doesn't need to be tightened crazy, but acts as an index to prevent movement of the block. Combined with red loc-tite, it's the best way to attach a set screw gas block, without cranking down on the torque.
 
Go with clamp on. I went with that on my last build and that block doesn't move and no, I didn't use the blue stuff. The gas block I went with is a Yankee Hill Machine low profile block. If you go with it, it's the only block they have where you don't leave the gap for what would be the end cap if your rail isn't a free float. This block pushes all the way back to the shoulder and made alignment pretty easy. I found that out the hard way because I didn't get instructions with it and the bolt couldn't go back all the way and would close on an empty chamber as a result. Their website has all their instructions in pdf form. I snug the screws and have had that rifle/block in service for over a year and it goes to the range every month.
 
What is the best way to align them? I will be doing this in a couple days so it would be very helpful to know.

1) Put the gas block on the barrel upside down (but with the back towards the back) and determine how the gas port in the gas block interfaces with the gas port on the barrel. On many/most gas blocks, room was left for a conventional handguard cap, so without that cap you will need to leave a gap between the gas block and the shoulder on the barrel to get perfect fore/aft alignment. On some gas blocks (noted above) no room was left and you just push the gas block against the barrel shoulder. Note any gap you need - a feeler gauge measurement would be ideal, but you can probably eyeball it and be fine, the port on the block is usually much larger than the port on the barrel (unless you have a 300BLK barrel, or something funny like a 16" with rifle length gas).
2) Put the barrel in your upper with the pin in place at the nut area, and confirm that the gas port is pointing perfectly vertical. It should be, and will on any decent barrel.
3) Install the barrel in your upper per whatever directions.
4) Install the gas tube into the block before assembling it onto the barrel - not required, but will usually make things easier.
5) Install the gas block onto the barrel. Align it perfectly vertical based on eyeball, straight edge use, or fancy tools if you're a machinist. If it's not a sight base, the vertical alignment only needs to be good enough for the gas block port to fully cover the barrel port, and again, the barrel port is usually much smaller than the block port. Align the gas block fore/aft based on whatever gap, or no gap, is needed per step #1. Again, a feeler gauge measurement would be ideal if there is a gap required.
6) Tighten the gas block clamps. On non-serious-use ARs I have not used any locking chemicals and haven't had any problems. For a serious-use assembly I would probably want to use Rockset, since it's highly heat resistant but also removable without destroying anything. Blue or purple Loctite weakens at gas block temperatures, and red Loctite makes disassembly a pain, at best.
 
I recently got a kies brand clamp on gb and it made installation a breeze on my rifle length gas barrel and 13" hand guard, however, I'm going to a 16" with mid length gas and no way will it ever fit under the HG I've got (cheap utg;) now so looks like I'm going back to a set screw. Might want to keep that in mind. If that's not an issue then clamp on is for sure the way I would go.
 
I recently built two ARs and I used clamp on for both. One rail was Seekins bar and the other a ymh. Under the Seekins went the vltor gas block,and I can't remember what I used under the other, but they both fit fine for me. Its easy to line up the gas port I just made marks on the barrel and the gas block for center. I might have considered set screw style if the barrels came dimpled, but after five hundred rounds they haven't slipped and are working great.