I have two 10.5 inch Nitrided finish barrels and two Odin Works nitrided finish low profile gas blocks for a couple pistol builds. I slid both gas blocks on the barrels and both slid on and rotate freely on the barrels. My previous builds have used WOA stainless barrels and Troy or MI low profile gas blocks. Those were all snug fits and required a hardwood block and small hammer to fit. Both 10.5 inch barrels measure .750 exactly at the gas port. The internal diameter of the Odin Works gas blocks measured .752 and .7535. Odin Works states the internal diameter between .7505-0.751. Is this going to be a potential problem or is this within an acceptable range?
How are you measuring the ID of the blocks? What tool?
Based purely on how the gas block seats by hand, it should be very snug on the actual gas block journal.
If I can turn it easily by hand, it’s not going on my gun. That’s my personal opinion…It’s served me well.
I am using the inner dimension claws on a set of digital calipers.
Yep. I just replaced a gas block on someone’s barrel for that reason. The block was sloppy and there was no doubt that it contributed to the short stroking. Some of the most consistent blocks I have seen are the BCM, Sadlak and Geissele. Geissele seems a little larger, but you do have the option to pin it and two set screws.
Exactly. Another block that fits properly is Clint’s Black River Tactical micro pin gas block. Nice and tight. His was tight enough that one could probably do away with one set screw and no pin.
Forgot about his, you are correct.
Thanks for the mention guys. 
The clearances and tolerances in the gas system are some of the tightest in the whole AR design.
The gas block should fit closely with both the barrel and gas tube.
The gas tube should fit closely with the gas key.
With these parts, a nominal clearance of .001" is just about perfect.
Parts with clearances of 2-4 thou will leak excessively and definitely cause issues.
Clint, wouldn’t a set screw block, like the OP has, eliminate the need for a perfect fit? The screws will pull the GB tight against the barrel. Not trying to make excuses for the loose block but in his case it probably doesn’t matter.
Double Post
IMO, no.
Practical experience shows that proper fit does matter.
Set screws will also do nothing for the gas tube fit.
As an example, why did the short stroking issue go away when IG replaced the loose block?
I contacted the manufacturer. The response is below. I was thinking along the lines of GH41 in that the set screws would seal the block to the port once tightened. The problem with that is I believe it would cause about half the gas block to be out of contact with the barrel as I have pictured below (albeit on a much less exaggerated scale). That doesn’t seem like an ideal way to secure the gas block. At this point it seems my options are to return it to the dealer for an exchange with a 15% restocking fee or mount them and hope for the best. Since these are for 10.5 inch barreled AR’s I really didn’t need to add variables into the gas system like this. Odin Works seem to get almost across the board good reviews on this block so maybe Im missing something but I trust the expertise here. Personally I don’t mind scratching the barrel up a bit when I mount a gas block. I just want a tight seal.
Michael,
The ID of our low pro gas blocks are .7515-.7520". The feel of the block with a difference of .001 is the difference of having to twist it on (which many customers don’t like because it can leave a scratch) versus sliding right on.
Can you try them out and let me know how they work? We ship about 1500 gas blocks a month and we have not had a single issue of one leaking.
Keep me posted. If they don’t work flawlessly for you, we will figure something out.
Thanks!
John
ODIN Works
Sent: Saturday, January 17, 2015 4:37pm
To: Info@ODINWorks.com
Subject: Problem with low profile gas blocks
I ordered two Odin Works low profile gas blocks from Joe Bob’s Outfitter’s for two .750 diameter AR barrels. The internal dimensions on both gas blocks are too large. Both gas blocks are loose and move freely on either barrel. The internal diameters according to my digital calipers are .7520 and .7535. Your help would be greatly appreciated.
Thank you
That’s the diameter of our “oversized” blocks that are for use with coated barrels.
Many barrel prints call out .749 +/- .0005
I think Im going to dimple the bottom of the barrel for the set screws and use a ton of red loctite on the smallest one and return the larger. Hopefully that will work.
I’m going to caution you on using a ton of loc-tite on those screws. When you use a lot, it has a tendency to wick out of the screws and dimple and into between the barrel and gas block for even more bonding area. I only use blue 242 on my gas block screws and one time used a bit too much. The next time I went to swap the barrel nut (for a lighter one) on that gun I couldn’t get the gas block to budge after taking the set screws out. I ended up having to put a propane torch (usually use a heat gun) on it for a good amount of time and then it still wasn’t easy to move the gas block. I tried clamping the block with some channel locks to see if I could twist it to break free (didn’t work), also tried tapping the gas block forward with a hammer and punch at the rear (didn’t work), and finally was able to get it to work by hitting the gas block at the top which rotated it ever so slightly to break free from the loctite.
When I slid (tapped) the gas block off I could see where a bunch of loctite had wicked between the gas block and screw and held everything together.
I built an AR for a friend last fall that had an Odin barrel and gas block and the fit was very tight (tighter than any of my BCM, SLR, V7, ect.) blocks.
I wasn’t referring to the loctite on the screws, although I will use plenty. My intention is to hose that entire gas block down with red Loctite so it doesn’t budge. If it never comes off again then all the better. What chaps me about the gas block is their website states the Internal Diameter range as 0.7505-0.751. John at Odin works tells me .7515-.07520 but mine are .7520 and .7530. If they were .7505-.7510 as represented when I made the purchase this entire thread would not exist.
If you’re going to do that, you should use the green sleeve retainer formula. If you do, you might as well weld it on. Seriously.
You answered your own question. Per the mfgs. tolerances, both gas blocks are out of spec. Exchange them or return them for something that is accurately and consistently manufactured.
Remember that he is measuring the id with a caliper. Not the most accurate tool to use even if it is a good one!
Ok, so what is the most accurate and practical method for measuring the internal diameter of a tube then?