I may look stupid, but I'm not dumb

So I finally got all the pieces of the Uzi made and fitted, and working the way they're supposed to.  The only thing left to do was test it before paint(because I didn't want to paint it and find out I still had to grind on something).  While I am prone to making poor decisions, I try not to do dangerous things with guns.  Especially guns that I've made.  Double especially guns that I've made that have essentially just sheetmetal between explosions exploding and my face.  So what's a guy to do?  Get a long rope and hide behind a tree of course.  So I clamped the gun in a portable workbench and tied a rope around the trigger and pulled it from behind a big tree.

Started with one round in the gun to make sure it wouldn't explode, then stepped up to two and then three to make sure it worked as a proper semi-auto.  So how did it go?  Well, it didn't explode, and every round that it chambered fired.  But it also didn't work great.  Just about every other round FTE'd.  Stovepipe after stovepipe as the spent casings didn't want to leave the gun.  I also noticed that the casings that did properly eject didn't go far, maybe a foot or two.

I spent some time troubleshooting, tweaking my top cover clearance(which should be around .010" ), making sure everything moved nice and free, testing both mags I have and getting the same results, and finally thinking that maybe my new bolt actually needed the big ejection scallop cut in it that the factory semi Uzi bolts have(which I very much didn't want to add). 

And then I remembered to actually watch the video I'd taken.  Seeing it in slo-mo, it was clear that the bolt was short cycling, i.e. not going back as far as it should.  Between the short cycling and the spent casings not ejecting with any real force, it occurred to me that maybe the gun was fine, but the ammo wasn't.  Up to that point, I'd been using some Armscor 124gr FMJ that I bought many years ago but never used when I started a Suomi project(that never got finished...).  While it's probably fine for other 9mm guns, it just didn't seem zippy enough for the heavy Uzi bolt.  So I bought a box of Winchester NATO 124gr FMJ, which the internet told me was pretty hot, and my FTE problems went away.  Not only were the cases ejecting, they were now flying out and landing 8'-10' away.  Let that be a lesson, if something seems amiss with a gun, try some different ammo first.