M&P10 feed problem

[tcutlermd]

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. But is the same true of the heavenly ordained Black Hills 150gr Match?

Looking for a smith's opinion before I start changing gas blocks and bolts. Or should I leave it as is and accept that some factory loads are not going to work?

Thanks for your input.

TC

 

[LlindeX]

I'd venture a guess that your issue has to do with the alignment of your new gas block. How did you verify proper alignment when you replaced the factory block with the new one?

 

[Fastbolt]

The M&P 10 one of our snipers tested was fine with any of his normal ammo.

Suggestion (Hint) ...

Before starting to modify a new weapon, consider test-fire & function-testing before modifications are done.

That way, if stoppages start occurring after modification, you have a little bit better idea of where to start looking at probable causes. Better to have an established baseline of performance, right? Might be nice to know if the rifle would've run as intended & desired, with the loads you selected, with the original gas block.

However, it's certainly not surprising that one or another brand/load of ammo might not always provide for optimal feeding/functioning in every semiauto rifle. That's why we test-fire and assess. If the "problems" go away when other ammo used? There you go.

Also, if this is an agency weapon, you could ask to speak with the engineering staff at the factory and get some info about the various loads they used during R&D and continued production/development testing.