Odd Bullet Up Jam in NFA Based AR9

[Wvaughn7]

My dad is having a new jam that I have never seen anywhere before on here and thought I’d post to see what you all had experienced or what you think may cause this. So far it has happened with multiple bullets in RN, FP and SWC style just to eliminate that as a problem. It is only happening when there are less than 6 rounds in the magazines, but it does not happen every shot after getting that low. The bullet will turn straight toward the top of the gun and miss the chamber completely. I built me and him identical NFA STYLE guns and have personally never had this jam in mine over approximately 1500 rounds using the same magazines which are a mix of sizes from 17 round Glock, 27 and 31 round ETS and a 31 round Glock with a TF +10 extension. Both guns have unramped 16” barrels. 

[Nathanb]

 

 

not as extreme but pretty much the same thing. He ended up sending his back 

[Hi-Power Jack]

I'd start by changing out all the springs on the gun and the mags - cheap and easy,

and it just might work.      

[Wvaughn7]

Ok, I have brand new Glock and ETS mag springs I can swap in and try but will have to get some for the gun. It’s running a 7.5 ounce buffer which I think is a little heavy and has also been short stroked with 6 quarters. The gun only has about 500 through it so I wouldn’t thing springs would be bad that fast, but who knows what kind of crappy springs may be in the gun from the factory. 

[Photon]

Try a plunk test. Mine ran well for a few months and I started having ftf's. I was going to have my barrel reamed but bought a JP, running fine now. 

[Acer2428]

Why would a plunk test matter if it's not even making it to the chamber?

 

I would check your mag lips/opening. It's not a CRF, so there's only so much control any one piece has. Mag lips, mag spring, and mag catch/magazine angle are the first things I'd check. Does he have the issue with all different mags or can you narrow it down? If it's various and the same ones you're using, you'd have to look at a different buffer setup. 

 

I'm no 'smith, but I'd have to think the <6 rounds and straight up means the round is being presented too slowly for the short-stroke and the bolt is pushing on the round before it hits the feed lips, allowing it to torpedo straight up and out the front. Try backing out a few quarters to start with and see if that solves it. 

[Wvaughn7]

1 hour ago, Acer2428 said:

Why would a plunk test matter if it's not even making it to the chamber?

 

I would check your mag lips/opening. It's not a CRF, so there's only so much control any one piece has. Mag lips, mag spring, and mag catch/magazine angle are the first things I'd check. Does he have the issue with all different mags or can you narrow it down? If it's various and the same ones you're using, you'd have to look at a different buffer setup. 

 

I'm no 'smith, but I'd have to think the <6 rounds and straight up means the round is being presented too slowly for the short-stroke and the bolt is pushing on the round before it hits the feed lips, allowing it to torpedo straight up and out the front. Try backing out a few quarters to start with and see if that solves it. 

 

I agree that a plunk test has nothing to do with this issue, but I have done that and all rounds plunked fine in both guns. The chambers are very short and the rounds are only loaded to about 1.050 though. I hadn’t thought of the round not being presented to the feed lips quick enough. That the rounds could be torpedoing as you say sounds highly likely in my mind.