This is the last thing I can think of that might be causing my rifle to be acting the way it is.

For a brief lowdown if you don't already know.

Brand new Stag M4.  16" chrome-lined upper.  came preassembled from Stag with Bolt group/etc.  I built the Stag lower myself, using one of the regular 6pos stocks and bufers from The Tic on the EE.

Fired 90 rounds initially of Winchester Value pack ammo.  .223 FMJ 55gr

All 90 shot fine except for one where the bolt slid over the top of the mag causing a minor jam.

I go to the local range where I have to buy their ammo.  Winchester Q3131.  5.56mm 55gr FMJ.

First few rounds shoot fine, and then after that it's pretty much 2 at a time before it jams.  A round will get stuck between the mag and feed ramps, or it just won't even cycle one in general.  Pull the charging handle, cycles a round, and shoots fine for another couple.

I decide to try other ammo.  I get Federal American Eagle .223 55gr FMJ.  Shoot 40 rounds fine, but it doesn't lock the bolt back after the last round is fired.  So I pull the charging handle and it locks back fine, so it's not the mag.

So obviously the bolt is going back far enough to eject every time, but not far enough to strip another round off the mag, or engage the bolt catch.

Have a new buffer spring on order, but what do you guys think of the gas tube?  Does the residue look normal?

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This is the American Eagle ammo shooting just fine....

Here are the ammo boxes.

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End of current buffer spring


By the way, there was another guy with a RRA carbine shooting that Winchester stuff just fine.  Came in about a half hour after I did.

I went to the range the following week and it still did the same thing.  Sometimes it locked the bolt back with the AE, mostly it didn't, and Q3131 still acted the same after about 5 rounds or so.

Make sure the carrier key is tight and properly staked...

Quoted: Make sure the carrier key is tight and properly staked...

Quite a few people mentioned that.  How do I know it's properly staked?  I can assure you it isn't moving though...

ETA - Here's a couple more pics...

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Here are some actions shots...and a properly staked carrier: Scroll Down

whats with all the blood and semen on the table?

I've never seen that much carbon buildup on the outside of the gas tube.  It looks to me like the gas port on the FSB is too big or the tube is too small.  You are getting a huge amount of blow by around the gas tube.  I have put thousands of rounds through a single Colt upper and had only a fraction of the carbon buildup, most of which occured within the first few dozen rounds.

Put it back together and place a small bead of white grease around the FSB -gas tube junction.  If it blows it out you'll know it's not sealing.

Quoted: I've never seen that much carbon buildup on the outside of the gas tube.  It looks to me like the gas port on the FSB is too big.  You are getting a huge amount of blow by around the gas tube.

 I was praying that I won't have to send the damn thing off to Stag :(  I'm not messing with that kind of stuff myself.

That ruins my night.

ETA: I don't have any white grease.  I'll just take your word for it because it makes sense.  I'm just going to have to ship it back to them and wait forever to get my rifle back.

Quoted:  I was praying that I won't have to send the damn thing off to Stag :(

The carbon build-up looks normal for a rifle that's been shot a lot. If it worked up until that point it should have sealed itself.

This pic dubisteinspundloch.com/Gast%20ube/DSCF4931.JPG shows what appears to be a worn out gas tube. There should be a 'bell' of sorts on the end slightly greater in diameter than the rest of the tube. That increased diameter provides the gas seal inside the gas key to operate the rifle. It appears totally worn smooth - probably from improper installation.

Considering the gas key screws are improperly staked, that's my bet. Replace gas tube and stake the gas key screws. A 10 minute job once you get the parts.

Quoted: Quoted:  I was praying that I won't have to send the damn thing off to Stag :( The carbon build-up looks normal for a rifle that's been shot a lot. If it worked up until that point it should have sealed itself. This pic dubisteinspundloch.com/Gast%20ube/DSCF4931.JPG shows what appears to be a worn out gas tube. There should be a 'bell' of sorts on the end slightly greater in diameter than the rest of the tube. That increased diameter provides the gas seal inside the gas key to operate the rifle. It appears totally worn smooth - probably from improper installation. Considering the gas key screws are improperly staked, that's my bet. Replace gas tube and stake the gas key screws. A 10 minute job once you get the parts.

I'd rather just send it back to them and let them deal with it, just in case there is 45834098503945 other problems with the damn thing.

And I have only fired a couple hundred rounds through it.

I took off work to shoot this coming Saturday at the range which is only open once a month as well, which is extremely disappointing.

I'm praying that removing the gas tube doesn't void my warranty or anything.

ETA- Did a Google search and I see what you mean by the bell on the end.  Mine apparently doesn't have that.

www.skalar.org/ar15gastube.jpg

I went ahead and took a closer look at mine.  It appears to have a VERY slight bell shape to it.  I can only feel it, but is not visible.  Maybe because of all the carbon buildup on it.

M4A1,

Would you be able to borrow a spare gas tube with the "bell" on the end and see if that helps? A different tube with the bell on it might fit tighter in the FSB too. It beats sending it back and having to wait for a while. Just a thought......

Quoted: M4A1, Would you be able to borrow a spare gas tube with the "bell" on the end and see if that helps? A different tube with the bell on it might fit tighter in the FSB too. It beats sending it back and having to wait for a while. Just a thought......

I don't know where I could get one, other than my friend's rifle, and he just got it so I'm not about to tear it apart.  By the time I order one and have it shipped, I might as well just send it back and let them look at it.

By the way, this tube was very tight in the FSB the first time I removed it.  I had to use the "light grip with pliers and tap with hammer" removal method.  This is the second time I have removed it (now for picture taking purposes) and I still have to give it a very hard tug to get it out.  I just use one of those rubber jar openers.   By no means is it not a tight fit.

The ammount of carbon buildup on the outside of the tube does not concern me. However the wear at the carrier end does.

Quoted: The ammount of carbon buildup on the outside of the tube does not concern me. However the wear at the carrier end does.

I'm just going to call them tomorrow and send the damn thing back.  I'm getting sick of spending my time and frustrating myself over something that should have been checked before it left the factory.

Could it be a poorly drilled hole on the gas tube?  Would this TAD bit make a difference?

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You can see it's got a very tiny notch at the bottom.

You are losing gas somewhere in the system. If the gas key is staked propely and the gas rings on the bolt are good, then you are down to the gas tube or the gas port as the problem.

Quoted: You are losing gas somewhere in the system. If the gas key is staked propely and the gas rings on the bolt are good, then you are down to the gas tube or the gas port as the problem.

I posted pics of the bolts on the gas key above.  The thing feels solid.

I'm going to replace the gas tube.  See link two posts up from this.