I've heard that the PTR's are picky when it comes to ammo. They are designed to shoot civilian .308 ammo not 7.62 surplus. Have you found that to be the case with your PTR? This guy looks to have the same rifle as your first post. He talks about some of the ammo sensitivity issues his PTR had.
http://www.gothamsurvival.com/?tag=ptr-91-review
I'm not sure what's going on in that guy's rifle, but all three of mine have no problem with everything I've fed them, and odly, everything HE fed them. The only problems I've had is with indian/türk surplus and WQ3130. Like I said earlier, nothings perfect, and I know the other platforms have some ammo issues as well.
That said, that guy's story is pretty abnormal, even for a "finnicky PTR". Yes, the PTR has some issues with some types of ammo, but odly every type he mentioned isn't one...lol???

: PMC and PPU are candy.... He has a really abnormal problem there. He said he should have gotten a DSA, I hope he wouldn't have gotten one with a improperly built weak receiver, aluminium upper, shattering bolt, worn pins, stuck regulator, poorly made lower, or expects to shoot the same junk surplus ammo, or steel cases in it. See how easy it is to find problems? If you couldn't go to DSA's official site, or FALfiles, and read for yourself, you'd think I was making all that up...
Also, to a couple other points, there is a tapco AR stock made for the PTR. The Magpul PTR stock is god of them all, but I haven't managed to scrape up $200 for one yet...I'm going to eventually, but I'm looking at adding a GI to my PTR collection as another beater...The GI has no ammo problems, btw...
If it were up to me, PTR would built every rifle to H&K chamber specs, but they believe in it for some reason, the GI is the answer to the bitching about ammo...
Anyways, once you find the one box of ammo the PTR actually can shoot (LOL

) you can do things like this without failure:
I performed these tests prior to getting my other 2 PTRs, but well after breaking in this rifle. If I had gone by my first range trip and not allowed the PTR another chance, I'd be the first one to jump in these threads and call them sh*t, because my first range trip I was effing furious...