I have a new M&P10 with the following mods prior to firing the first round:
(1) Troy TRX 13.5 free float tube
(2) VLTOR low profile gas block
(3) Geissele SSA-E trigger
(4) Nikon Monarch 4-16x
The bolt was wet with Frog Lube when it came back from the gunsmith and I left it as it was.

Started with Hornady 125 gr custom lite in the factory steel mag (5 rounds per mag). Misfeed on the second round. First round extracted, 4-5 feet out about 90 degrees. The 2nd round was about half way up the ramp with the bolt jammed against it.

Switched to 10 round PMag. Tried again with same ammo. Same result. I assumed the "lite" loads were insufficient to properly cycle and I put them aside.

Swabbed the barrel. Switched to 10 round PMag with Hornady TAP 168gr AMAX. Scoped zeroed by the 3rd round. 1-2" groups. Four iterations, barrel swabbed after each set, 5 rounds each, no misfeeds.

Then factory mag with Federal Fusion 180 gr.
Four iterations, 5 rounds each, a few clicks up to re-zero and no misfeeds.

Now I was sure that the "wimpy girl loads" (my shooting buddy's choice of words) were the problem.

With scope near zero, it was time to step up the game. Loaded 5 rounds of Black Hills Match 150gr BTHP at $2 per round into the PMag. Much to my suprise, it behaved exactly like the Hornady 125gr Lite. The bolt jammed on the 2nd round half way up the ramp. With factory mag. Then the PMag. Then with more Frog Lube on everything except the scope. 2nd round failed to feed each time - half way up the ramp with case rammed and dented just below the shoulder by the bolt.

Switched to 10 round PMag with Hornady Whitetail 150gr Interlock. Four iterations, 5 rounds each, no misfeeds. Scoped zeroed by the 3rd round. Tightest groups yet 1-2" with many touching and some near same hole. She defintely loves this ammo. Good to know because (1) this is a hunting rifle and (2) it was the cheapest of the 5 that I tried.

So, I'm guessing she misbehaves with the Hornady 125gr Lite because it's underpowered. Is the same true of the heavenly ordained Black Hills 150gr Match?

Expert opinions, ponderings and pontifications welcomed.