Has anyone here ever encountered a defective YHM-9384 gas block?

[Harold]

I've built five AR-15s which have all used YHM gas block front sights and I've never had a problem with any of them (or any other YHM product) until now, when I'm trying for the first time to use a YHM low profile gas block on my (apparently cursed) LR-308 project.

I just ruined a roll pin and bent my 5/64 roll pin punch (I should've stopped pounding on it but I was talking to someone and not fully paying attention to what I was doing).

Apparently the gas tube pin hole in the gas block is improperly located; it is not on the diameter of the gas tube. To put it in geometric terms, the axis of the gas tube pin hole would be a chord which is parallel to the diameter but offset from it by 0.010" or something like that (in this case 0.010" closer to the bore of the gas block).

So far in trying to put this LR-308 upper together I've replaced a barrel and a bolt carrier assy., and I've sent back a too big/not-as-advertised barrel nut and associated hardware and handguard. The only part that I haven't had to return/replace *so far* is the Aero Precision M5 upper receiver, but in light of everything else that's happened I'm beginning to suspect that it too may have some treacherous latent defect that I just haven't discovered yet.

I think I'm on the verge of cutting my losses by giving up on this project.

 

[Stephen G]

Thats the stuff which makes it fun though

 

[Bongo Lewi]

No. But I have had issues with matching barrels to gas blocks. I have seen poor fit and different sized ports in barrels (for the same caliber) that gave me fits trying to get the gas system working reliably. I would recommend running an adjustable block on any large frame AR platform.

 

[Harold]

Thats the stuff which makes it fun though

I'm up for a mild to moderate challenge, but the steady stream of faulty parts and pettily dishonest sellers I've encountered so far takes the fun out of it for me . I have a low tolerance for that. I will never again buy anything from "Windham Weaponry."

I emailed YHM about the gas block issue and they immediately sent me a Fedex shipping label so hopefully I'll receive a properly machined gas block by next week some time.

No. But I have had issues with matching barrels to gas blocks. I have seen poor fit and different sized ports in barrels (for the same caliber) that gave me fits trying to get the gas system working reliably. I would recommend running an adjustable block on any large frame AR platform.

Based on what I've learned so far, that sounds like sage advice. My biggest concern right now is getting the gas tube geometry right so that it's properly aligned with the carrier key and the engagement of the two occurs without any mechanical resistance or deflection of the the tube. (In my previous AR-15 experience, this was not a big deal but this thing is more difficult). If I can get to that point (using the cheap YHM gas block) I will probably invest in an adjustable block).

 

[Harold]

Just in case anyone's interested, I should mention that I used a set of $20 Harbor Freight numbered drill bits as a quick and easy way to check the gas block. I put a 5/64" drill bit through the roll pin hole (a number 47 drill bit should work here also), and then by trial and error I found the largest size drill bit that would fit both above and below the 5/64" drill bit. (The test drill bits are inserted perpendicular to the 5/64" drill bit, i.e. they're where the gas tube would be). On a good gas block, I found that a number 55 drill bit was the largest that would fit both above and below the 5/64" drill bit, whereas on the defective gas block, the drill bit sizes that would fit above and below were different. I think there is probably enough give in the roll pin to accommodate an offset of a few thousandths but not beyond that. And BTW that numbered drill bit set is useful for measuring other things like the barrel gas port size, etc.

Edit: I looked at my notes, and in the case of the bad gas block, the largest drill bit which could be inserted above the 5/64" drill bit (which stands in for the roll pin) was a #53 (0.0595" diameter) and the largest drill bit which would fit below it was a #57 (0.043" diameter). So the gas tube roll pin hole was offset from center by about (0.0595 - 0.043)/2 = 0.00825," which is way too much.

 

[Harold]

According to someone I spoke with today at YHM, the gas block I returned was found to be (to my amazement), "in spec., but towards the high end" (or something like that, according to their "quality" dept.). But luckily for me they're graciously going to send me another one anyway (some time next week). So there must be something seriously wrong with the several different gas tubes I tried to install into the subject gas block (both of which were somehow easily installable into a similar product - a YHM gas block front sight); or the culprit might be my fickle roll pin punch which is either just not a reliable team player or apparently didn't get the message that the gas block really is "in spec." and instead arbitrarily decided to bend rather than to install the pin.