ar15 gas problem

[edward_kaleigh]

hey everyone, today i want out to shoot a brand new bushmaster predator upper. i already had a bushmaster moe carbine and just bought the predator upper to put on it to shoot longer ranges. well the upper was short stroking. i thought maybe it was just needing broke in and ran 150 rounds threw it but it just kept up. sometimes it would not pick up a round and almost always would not lock back on last round. just to make sure while we were at the range we tried a different bolt in the upper and spring and buffer and on a different lower and nothing improved.
so when i got home i broke the gun down, i took of the free float tube and noticed about 1.5 to 2 inches up the gas tube from the gas block were carbon marks also in the free float tube. so i took of the gas block and the gas port was clear and .087 in diameter witch seems to be good but the gas block to gas tube fit seemed loose. the gas tube was also normal diameter. i cant seem to think of anything elce but the gas block. i do not know how much carbon is normal on the gas tube by the gas block but is seams like a lot. my other ar only has a small amount maybe 1/4 inch carbon mark on the tube.
i would rather not send the gun to bushmaster, it would just seem be to fix it myself. if a 30 to 40 dollar yankee gas block will fix it that is much easier than sending it back.

 

[jscandale]

Ed,

Answering questions about flaws in a gas system without having the rifle in hand is a bit tough since there are so may variables, however I'll try to give you some good info and you can make a better informed decision.

You mentioned that the current gas port diameter is .087" and I am assuming that it is a 20" bbl with a standard rifle length gas tube. If that is the case, I can tell you that my standard gas port dimension for all service rifles is .094".

You also mentioned that the gas block seems loose. Is it a set screw type gas block or just a milled A2 front sight that Bushmaster frequently uses? The reason I ask is because a standard A2 port location is .270" from the shoulder where most commercial blocks are .300" Not really that big a deal, but it's something for you to know if replacing the gas block. If you want to modify the milled A2 type gas block very quickly and effectively, just run an 8-32 tap through the hole in the bottom of the rear ring directly acrsoss from the gas port location and insert an 1/8" 8-32 set screw. Once it is in place, use green loctite around the rings to lock it in place.

Once you have achieved the gas block problem and let the loctite dry, shoot the rifle and you will probably notice a minimal amount of carbon around the gas tube where it enters the gas block. Don't worry about it. Once you fire it about 100 rounds or so, all of the tiny air spaces will self seal with carbon blowback and you won't have that issue.

Hope that info helps.

JS

 

[edward_kaleigh]

ok i double checked the gas port .088 to .089

from shoulder to gas port is .276 on barrel (and yes it is the milled a2 front sight post)

and i did not mean the gas block is loose on the barrel, i meant the gas tube seemed loose in the gas block, and i had about 150 to 175 rounds threw it and it did not seal like you said.

and thanks for the heads up on commercial gas blocks, i did not know there was a difference

 

[edward_kaleigh]

also 20" barrel

 

[jscandale]

If it's loose in the block to the point that it wiggles, I'd replace the either the block or the tube. The hole in the block should accept a .180" drill bit, but no larger.
Even at .088 or .089", it's on the small side. You'd be surprised on what a few thousands will do especially if you are using a medium burning powder and lighter bullets.

JS

 

[jscandale]

If you would like a YHM pinch type block with .030" milled off the back, let me know. I usually keep them in stock.

JS

 

[chuckbuster243]

If it's loose in the block to the point that it wiggles, I'd replace the either the block or the tube. The hole in the block should accept a .180" drill bit, but no larger.
Even at .088 or .089", it's on the small side. You'd be surprised on what a few thousands will do especially if you are using a medium burning powder and lighter bullets.

JS

+1

 

[edward_kaleigh]

OK, i called bushmaster, i told them about the gun short stroking and they went threw out all the normal questions, different mags, ammo ect. Then i asked them what there normal gas port size was for rifle gas systems. he looked at a chart and said .093, then said hold on, when he came back he backed off the measurement and said send the gun in for "evaluation". Then i asked what is the turn around time for repairs and he said 6 to 8 weeks. To me that is way to long.
i also called to gun smith across town and asked to gas port size and he also said .093 and said he would turn the barrel if i wanted to accept after market gas blocks for 50 bucks, if i need to change it out. so i have a drill bit index that has .089 .093 .096 so i guess i have a project next weekend. i have a .087 by the way, so i guess i start working it up.
does anyone have any other suggestions.

 

[jscandale]

Ed,

Here's the quick and easy fix right at home. Remove the gas block to the point of the gas port being exposed. If you have some numbered drills, use a #43, then a #42 to gradually open the hole. Use a tap handle or a small drill chuck to twist the drill. Insert a 3/16" wood dowell in the barrel so you don't go through and nick the other side of the bore.
Your problem will be solved!

I'll add that after I drill the gas port, I always finish ream to size with a chucking reamer which you can also do if you care to buy the reamer, but you'll be just fine with the drill reaming method.

JS

 

[edward_kaleigh]

thanks everyone ;D PROBLEM SOLVED ;D

i got my dads drill bit kit for machine work and drilled it out to .093 and it was working half the time, then took it to .096 and works great. Thanks jscandale for the tips, i used an old brass rod to protect the other side of the barrel. Now all i have to do is buy a nice scope and mounts. 2 days is a lot better than 6 to 8 weeks. i lost a lot of respect for remington, because i have had to get a ruger repaired and it took 1 1/2 weeks out and back to my door. to me it is not the end of the world if a gun has a problem that is a mass produced gun but i do want service in a timely manner.

i decide to ask the question here because i have been lurking and noticed everyone here is knowledgeable and not a smartass. a lot of ar forms are just full of morons.

thanks great forum

 

[jscandale]

I am happy it worked out for you.

JS