My sons 20" A2 upper has been short stroking, failing to lock back and failure to come back far enough to strip round properly. The problem is somewhat intermitent and will function properly including lock back probably 50% of the time.

I have swapped around uppers, bolt/carrier groups, buffers and buffer springs all to no avail. The other day I decided to check the alignment of the gas port to sight tower hole, that is right on the money, but after looking things over carefully there is definitely a heavy loss of gas from the sight tower where the gas tube installs. Is there any way to tighten this up to correct the problem? Or at least to temporarily get a better seal for diagnostics?

Thanks for your help.

Jeff

New gas tube??

I tried that also, several.

Is there some sort of sealent that I would use around the tube such as Lok-Tite?

Jeff

What brand of ammo were you shooting?

the hole for the tube there is one of the more precise requirements believe it or not...

the blue prints call for it to be cut with with a reamer... .180 iirc, off the top of my head.

A number 15 drill bit is .1800 and many think that is cool, but the bit actually makes the hole a tad bigger... I suspect this is your problem.

If it is not a FA gun, you should be okay with a shot of high temp stud locking compound when you install that gas tube... but just write off getting the tube out again without damaging it.

Gunzilla,

Tha t sounds like the info I need, the hole does seemto ba a bit wallowd out.

Ammo was varied, Olympic 55 grain stuf and SS109, Barnaul 55 and 62, handloads, FN ball, maybe a couple others.

Jeff

Quoted: Ammo was varied, Olympic 55 grain stuf and SS109, Barnaul 55 and 62, handloads, FN ball, maybe a couple others.

www.ar15.com/forums/topic.html?b=3&f=16&t=202971

www.ar15.com/forums/topic.html?b=3&f=16&t=201684

I know all about Olympic but have shot nearly 5000 rounds without failure in any other rifles, this rifle malfunctions with everything and I wouldnt class FN ball as problematic, Barnaul has been awesome and as accurate as my handloads in my Vmatch and heavy barrel varmint gun.

Jeff

I had the same exact problem when I built my 24" AR.  The gas leak is evident from the blacken barrel and gas tube around the gas block.

I fixed it by putting "small" amount of epoxy around the gas tube (behind the gas port hole) before I reinsert the tube into the gas block.  Some epoxy are forced out providing a seal around the gas tube.  Once dried, take it to the range.

I have not had any more cycling problem since.

That sounds like a good idea, I have some JB Weld on hand and will give it a try this weekend.

Thanks

Jeff