Home Forums Hunting & Shooting AR and Tactical Rifles Problems with 9MM AR

I pieced together a 9mm AR last year and have been happily shooting it since. It has a polymer no-name lower with a decent trigger, the upper was assembled by the same friend who built the lower. Everything functions as it should and it shoots well with the DHA ammo I bought last year. I did install a 9mm rated buffer.

I decided to load some 80gr Barnes TAC-TX bullets today. Using Hodgdon's data the COL is 1.025" and I loaded mine to 1.030". Almost every one of them jams between the front of the bolt, the magazine feed lips, or the bottom of the barrel. When they do rarely feed in the bullet gets jammed deeper into the case. The only way I have found they stay the same length is if I drop one into the chamber manually. After experimenting with heavier crimps and cutting cannelures into the bullets I have about given up. I tested some of the manufactured ammo and while it feeds flawlessly all the bullets are jammed into the cases too.

What's the problem here? Is my main spring too heavy? Would a 300BLK subsonic spring be more appropriate or are 9mm specific springs made for these applications?

Thanks, Dinny

Since it's been sitting here for a week with no answer, I'll answer it for you. And it's a combination of things. Everything worked fine before you changed the buffer and started making those short light bullets, so I'm going to say those two things are directly the cause of why it's not working anymore.

As to what I think is causing the gun to not work anymore:

1. Your loads.

2. The overall length of your loads

3. The heavy 9mm buffer may be contributing to it, but I think it's going to boil back down to both #1 and #2.

Since factory loads feed ok, it’s got to be something having to do with your loads.

Remember 9mm headspaces on the mouth of the case so you don’t want to crimp very much, just enough to take out any flare you might have used to ease bullet seating. A little taper crimp is what you need.

Since the bullets are being seated deeper during feeding, you’ll need to get more neck tension. A smaller expanding plug for your expander die is called for so you might want to machine it down or use a drill to run it against a whetstone. Maybe try to figure out a way to flare the case mouth so you can start bullets, but not expand the area right below the case mouth.

I worked in the AR industry for a company that build everything from raw stock, except some screws and springs. I was on the design team for products, including a 9mm PCC. PCCs are finicky about ammo, particularly the shape of the bullet. This has a lot to do with the feed ramp profile on the barrel. Rudy at Macon Armory has barrels with a feed guarantee; he used to rework feed ramps if you sent your barrel in, don't know if he still does.

The bullets getting jammed into the cases, even on the ones that feed, are symptomatic of a feed ramp issue, and it's dangerous (can give high pressures).

PCCs that are straight blowback have a lot of reciprocating mass, more than regular ARs. They are hard on fire control groups (pins have a lot of force on them) and bolt catches (if you have last round bolt hold open). Plastic wouldn't be my choice for a PCC lower for those reasons. You might start getting multiple rounds fired on one trigger pull from FCG pin holes wallowing, or even the ring that holds the buffer tube cracking where it meets the top ledge of the lower.

Reloading for PCCs is the same as reloading for pistols. navlav8r's suggestion about crimp is good. Another is do the plunk test to make sure you have the correct length to ogive for your chamber.

Stop loading 80gr Barnes TAC-TX bullets.