View Full Version : Low profile gas block indexing
ilikeguns111
03-23-11, 18:25
How do you index a low profile gas block? I find it difficult to know if I have my gas block perfectly alined.
Also How do you know if your gas block requires a gap or should be pushed all the way back?
The low profile gas block I'm using is the Vltor clamp on one.
If you turn the gas block upside down, you will see the hole in the bottom of it. That exactly corresponds to the actual covered hole in the top of the block. Then perfectly center the upside down block over the hole (eyeball it directly from above in good light). You will see how much gap you need front/rear, and can take a feeler gauge measurement of that. At this point also, what I do is use a fine sharpie pen to mark a dot on the barrel at front center of the gas block so you know where the center of the hole is. What I also then do as a belt and braces measure is take the block off the seat altogether, and I use a metal ruler straight edge against the seat and make 2 parallel lines on the barrel which correspond to the left/right edges of the hole in the barrel. Extend these lines past where your gas block will go.
Then put the block back on, using your feeler gauge to correctly gap the front/rear clearance. Then, you can then center the block for left/right, using your dot mark and the two parallel lines to get it centered. A nice thing about the VLTOR blocks is that they have the symbol on them - and I find that assists you getting it exactly level. Once happy, I then torque the screws down to 55-60 in/lbs (using no loctite at this point). I then go to the range and test fire to make sure all is well. I then come back and remove each screw individually, degrease the screw and threads and use high temp loctite/rocksett and torque them back down.
Dirtyboy333
03-23-11, 23:52
Interesting. Thanks for the pointers bc I was wondering the same thing.
I've only witnessed one lo pro gas block install, so I'm far from an expert. But the inlet on the gas block was much larger than the barrel port.... so there was some margin for error in positioning the block on the barrel.
I have a vltor low pro on mine. Not the clamp on, but the one withthe set screws. It does require a gap. I didn't pat attention to this at first, installed it all the way back, and while the rifle functioned, it wouldn't lock the bolt open on the last round consistently. Realized my mistake, fixed the alignment and haven't had an issue since. Still need to get the jig to drill it for a pin.
I have a vltor low pro on mine. Not the clamp on, but the one withthe set screws. It does require a gap.
Worth nothing that depends as much on the barrel as well as the block.
As Markm said, the hole in the block is bigger than the hole in the barrel so there is some margin for error. Of the 4 that I have personally done for myself and friends, it has looked to me that the blocks would be ok all the way back on the seat; just a tiny bit off center but still within the overall diameter of the gas block hole. But different barrels may be different so you do have to check each and every time.
In any case, being a bit OCD about it, I make sure I do gap it correctly, however slight that may be :) I personally think that aligning these low pro blocks is the part of an AR assembly with the most potential for a mistake, so worth taking your time about it.
My first gas block install was a Troy Mk18 type with two set screws. I just visually aligned it so it was vertical and never had a problem. The opening in the block is larger than the gas port, as others have stated.
My last three were all Noveske pinned blocks. As long as it was visually vertical, and the pin lined up, rocksett on the one set screw and done.
If you turn the gas block upside down, you will see the hole in the bottom of it. That exactly corresponds to the actual covered hole in the top of the block. Then perfectly center the upside down block over the hole (eyeball it directly from above in good light). You will see how much gap you need front/rear, and can take a feeler gauge measurement of that. At this point also, what I do is use a fine sharpie pen to mark a dot on the barrel at front center of the gas block so you know where the center of the hole is. What I also then do as a belt and braces measure is take the block off the seat altogether, and I use a metal ruler straight edge against the seat and make 2 parallel lines on the barrel which correspond to the left/right edges of the hole in the barrel. Extend these lines past where your gas block will go.
Then put the block back on, using your feeler gauge to correctly gap the front/rear clearance. Then, you can then center the block for left/right, using your dot mark and the two parallel lines to get it centered. A nice thing about the VLTOR blocks is that they have the symbol on them - and I find that assists you getting it exactly level. Once happy, I then torque the screws down to 55-60 in/lbs (using no loctite at this point). I then go to the range and test fire to make sure all is well. I then come back and remove each screw individually, degrease the screw and threads and use high temp loctite/rocksett and torque them back down.
Probably the most detailed gas block attatchment i've ever come across. Blig plus on the Rocksett, I love the stuff. Where did the torque spec come from?
Where did the torque spec come from?
It was actually one of Grant's posts (from 3 years back - post #7 - thanks Grant :))
https://www.m4carbine.net/showthread.php?t=11660
I know VLTOR recommend's 40in/lb for their sight tower, which of course is different but I imagine they would recommend the same setting for the low pro...so 55-60in/lb is possibly a little much, but as stated I've now done 4 in total all with these same gas blocks (and my same OCD method, lol), and have had no trouble at all. As per what Grant said in his post, I doubt these will be moving anywhere.
Dirtyboy333
03-25-11, 00:22
I've only witnessed one lo pro gas block install, so I'm far from an expert. But the inlet on the gas block was much larger than the barrel port.... so there was some margin for error in positioning the block on the barrel.
Sweet. That's what I like to hear. My DD block will be here soon and installing it is the only part of my whole 1st build that had me a lil nervous and it's not a " connect an upper/lower" build its a part by part build.
Ive never seen an unmounted gas block and was actually just thinking that the blocks port could be made larger to make installation easier and u just confirmed that. Ha
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