So I built/assembled a M16A4 clone.  Del-Ton 1/9 twist 20" barrel and gas tube.  Everything else except for the fire control group is Palmetto State Armory (upper, lower, lower parts kit, BCG, upper parts).

























 

Can you be more descriptive of your failure to feed?  Does the bolt simply fail to pick up a round and leave the chamber empty? Does the bolt ride over the round in the magazine and hang up on the side of the cartridge in the magazine?  Does the round hang up under the feed ramp?  Does the round hang up on sharp edges on the feed ramp?  Does the round hang up inside the barrel extension against the breech face?  Does the round mostly feed, but just fail to chamber completely?

Pics would be good.

It will extract and eject the previously fired round, but the bolt doesn't always pick up the next round.  The bolt rides over the round.  It's not jamming at all.


 

It might be short stroking, where the bolt comes back far enough to ejection, but not quite far enough to get behind the next round to let it present and feed.  You can test for that by loading a single round into the magazine, then insert the the mag, chamber and fire.  If the bolt doesn't lock back on the now-empty magazine you're short stroking, and that's a gas issue with the upper.

That's my best, first guess as to your issue, since it's only having problems with Tula and BB - which tend to be loaded less hot than most.

With it only occurring every five rounds or so, it's like it's ALMOST got enough oomph to cycle, and that may ease over time with break-in and better lubing, and perhaps drop from a heavy buffer to a lighter buffer if you're running something like an H or H2 buffer now.

Interesting... their was an instance of the bolt not locking back on an empty magazine.  It happened at least once with a brand new pmag.  But I don't remember if it happened more than once.  I chalked it up to a bad magazine.

Since I don't use steel cased ammo in any AR's, I'm partial to factory brass cased or my own reloads, which I've been reloading for 30+ yrs.  Tula is well document for being a bit underpowered..if I were you, I'd shoot it or trade it away on some good quality brass factory ammo.  Get into reloading as well...you will soon find out that you can reload your own ammo, and be just as accurate or better, than paying top dollar per rd.  Just my opinion, hope it helps,  

Rifle buffers should be more or less identical - all the variability comes with the carbine buffers.  See if it's short stroking, and maybe try extra lube until you've got a few hundred rounds through it to break it in.

I have used Silver Bear 55gr. HP ammo and it runs great.  Wouldn't hesitate to buy more.  Don't know about the brown bear.

My mid length M4, which I had also taken out that day, shoots steel cased ammo perfectly fine.  But I had read or heard that it could be the source of my problem.  


 

Some rifles don't run underpowered steel cased ammo reliably, others eat everything. I'm gonna bet you have one of the picky ones, i'd save the steel for the m4geries and shoot brass out the a4 clone.

Alright.  So yesterday is the first time I've gotten another chance to take my rifle out and fire it.