Hi guys, just recently finished my first build.



Being my first build and AR, and that I rushed it a bit, I bought a barrel that came with a low profile gas block, which I didn't realize wouldn't really work with magpul handguards. So I got a round handguard cap, and did some measuring to ensure the gas block's hole would still encompass the gas port on the barrel after being displaced by the cap. Took it to the range, and it doesn't cycle correctly. Most of the time it cycles enough to eject the round, or have it jam in the ejection port, but doesn't strip a new one. Only a handful of times would it actually eject the round and strip a new one. I narrowed it down to a gas leak between my gas block and the handguard cap. If you look closely at the following picture, you can see the lines on the handguard cap indicating the leak.



I'm looking to upgrade to an iron sight, and my LGS has this:
http://www.brownells.com/rifle-parts/gas-system-parts/gas-blocks/yhm-9395-front-sight-gas-block-no-lug-sku100002077-21446-46689.aspx

So my questions are: Will the YHM gas block + handguard cap + magpul handguards give me the same trouble? Or should i just keep my low profile and develop a taste for different handguards?

Thanks.

My guess is you don't have a gas leak, but the gas block is not sitting far enough rearward and part of the gas port on the barrel is being "shrouded", and thus not allowing enough gas to exit the barrel and down the gas tube.  You may need to ditch the handguards and go with a FF setup.

It is my understanding that low pro gas blocks are designed so that a hand guard cap can be used and the gas holes will still line up. The hole in the gas block is supposed to be larger than the barrel gas port.
If gas is leaking between the gas block and the outside surface of the barrel, that is a different problem. I'm not sure how that would be sealed. High temp gasket material may work?
One way to see if air can pass from the barrel down the gas tube is to block the chamber mouth, blow air into the muzzle and feel if air is escaping the gas tube in the upper receiver. The gas port of the barrel may be undersized.  

Any of the above could cause short stroking of the bolt carrier.

disassemble your bolt carrier....drop the stripped carrier and key into the upper...feel if it has ANY inteference with the gas tube......if it does find out why......., it could be a slightly twisted gas block.....ony take a couple of thousandths to be a significant misalignment down at the bolt carrier......Make sure that barrel nut is aligned.... when you install the barrel nut.....get it close and slip the gas tube in so it is at an angle......then use it as a pointer to align the notch in the barrel nut with the barrel.....

I had same issue that boiled down to misalignment
Sliding the block forward you can see the soot pattern around the gas hole on the barrel.

(There may be a better way but I didn’t look)
I re aligned the block by using a piece of vacuum line slipped on the gas tube (with BCG out)
Blew on the hose as I moved the block around ... got it GTG no problem

Old thread, but for what it's worth, the YHM gas block does work with the round handguard cap. My rifle functions flawlessly now.