gas leak at gas block. Need help.

[thenodnarb]

Finally replaced my barrel after "blowing up" the last one with a couple squibs.

My last barrel had a vltor low pro gas block, and the gas tube was a cut down carbine tube(to the pistol location). This time I tried a cheaper YHM block with another cut down carbine tube. Since the YHM has a gas tube hole that is drilled through, I had to plug the back end with a set screw(screwed directly into the gas tube).

I test fired it yesterday and was getting basically no BCG movement. This was with 9.3g of 2200 behind a 168grain hot cor. Previously I was able to cycle with only 6 grains of 2200. I'm using an A2 stock with a carbine buffer spring, and all the weights removed from the A2 buffer. The only thing that has changed from the last setup is the gas block. I tried plugging the chamber with my finger and blowing into the bore. Most of the pressure escapes around the gas block somewhere.

I ordered a pistol length gas tube and its on the way and hopefully it fits my barrel correctly. I'm curious to hear from other people to see if they can think of anything I may be doing wrong. I think I may be leaking gas from where the roll pin goes through the gas block. When I first drilled the hole, I think I may have drilled it slightly too big so the roll pin is really only holding the tube in but not sealing around the hole drilled.

thanks for your patience reading this and any advice you can give.

[mstarling]

If the gas tube isn't quite long enough or the fit to the gas key is not quite right, you will see anything from short stroking to no BCG movement. Have used the YHM gas block with no problems but required a good tube.

Did you mean 2200 or 2400 for the powder?

You mentioned a "blow up" ... did you stick bullet(s) in the bore or get a detonation? What load(s) were you using that gave you that result?

[rsilvers]

I think you need to wait until you have a real gas tube and then see what happens.

I can't see how a carbine buffer spring is a good idea. It it too short. Also you should put back a normal buffer. Why are you doing all these strange things - to be able to use really fast powder to be quieter?

[thenodnarb]

woops. was using 2400.

I shot multiple squibs down the barrel with extremely light loads. I was successfully shooting 6 gr or 2400 with 168 BTHP hot cors. Then I switched to a 220 grain nosler partition with only 6 grains of 2400. I was trying to get it as quiet as I could without a suppressor (since i live in Komifornia). What I failed to realize is that the partition has a very long part of the bullet that contacts the rifling which caused a considerable amount of drag. The loads were so light they didn't blow up the barrel but rather escaped through the gas tube and the chamber I guess. What stopped me was that the last squib blew so much pressure down the gas tube that it sheared off the gas key and jammed up the receiver. luckily there was no damage other than to the barrel and gas block and gas key. I was able to save the whole BCG by just drilling out the gas key bolts and bolting the gas key back on. The barrel, gas block and gas tube were all damaged.

back to the new issue: I'm pretty sure the gas tube is lined up with the gas block since I was able to mark and drill the gas tube while it was on the gas block(the set screw mounting holes line up with the gas tube hole). I made sure the gas tube fit into the carrier straight and to its full depth. I'm also pretty sure the gas block is lined up with the gas port.

Shouldn't the gas block and tube be fairly air tight? I know some gases can excape around the block, but it should be better sealing than what I've got going on.

[mstarling]

I do not understand what you have told us here. There should have been no need to put a drill bit down the hole in the block to allow the gas tube to fit ... so there should be no problem with proper fit of the tube to the block.

There needs to be a notch for the gas block pin, and a hole in the tube to allow gas to flow out of the barrel port into it. Is that hole properly aligned?

I suspect the new tube will fit better and should certainly have the gas port and pin notch in the right place.

[thenodnarb]

Originally Posted by rsilvers

I think you need to wait until you have a real gas tube and then see what happens.

I can't see how a carbine buffer spring is a good idea. It it too short. Also you should put back a normal buffer. Why are you doing all these strange things - to be able to use really fast powder to be quieter?

I've heard of other people doing this(on this site) to help with cycling. To be honest, it works. Its just not working now because I have no gas directed back into the action. I'm only posting this because I'm concerned that a pistol gas tube wont be the correct length. I think that because...again....people on this site have mentioned that on their barrels, a pistol length tube wasn't correct and they had to custom make one out of a longer tube.

Kind of a moot point since I don't even want to bother with light loads anymore. I'm happy with 9ish grains of 2400 which is plenty for the bullets I'm shooting.

If the gas tube works, then great. If it doesn't fit, then I don't know what I'll do since i'm not really getting any helpful answers. I thought this stuff was pretty common for ar-15 whispers, but apparently not.

[thenodnarb]

Originally Posted by mstarling

I do not understand what you have told us here. There should have been no need to put a drill bit down the hole in the block to allow the gas tube to fit ... so there should be no problem with proper fit of the tube to the block.

There needs to be a notch for the gas block pin, and a hole in the tube to allow gas to flow out of the barrel port into it. Is that hole properly aligned?

I suspect the new tube will fit better and should certainly have the gas port and pin notch in the right place.

i'm clearly not explaining things right. I'll just wait for the gas tube to come in, and post a picture if things don't work out right.

[i8asquirrel]

Thenodnard
1st glad you didn't get injured when your weapon failed (thats some scary shit)
2nd I was running a carbine buffer in my whisper and was told on one of the gun foruoms that it could do what happened to you. luckily I changed it before any misshap. I run a standard length buffer that has had the weights removed to a weight of 1100 grains. works great!
3rd I run a pistol length tube on a 16 " barrel. I have seen guys using custom length tube 1.5" shorter than standard pistol lenght..
This is a worthwhile project,you will have alot of fun when you get the thing running. They are whicked fun

[sha-ul]

I think this is what he was referring to as the mishap



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