Hey everyone, new guy here not only to the site but AR's in general. I have a M&P sport 2 that I bought used from armslist. VERY good price btw! I have had the rifle for 3mnths and it ran PERFECT with all types of ammo. Bcg, buffer spring assembly, trigger, barrel everything still stock. All I have done is upgrade the furniture.
Shot great one day and the very next I have failure to feed EVERY single round. I have researched and worked my tail off trying to remedy this. I have tried everything from new mags to gas tube leak tests. I have swapped out bcg with a friends sport 2 with no results. I was wondering if anyone could help me with warranty info. Is the gun under warranty since I bought used?
Any advice is GREATLY appreciated in advance!

I would call S&W and tell them what it's doing. They will then ask you for the serial # and your mailing address so they can send you a FEDEX shipping decal.
I have bought a few S&W firearms in the past and S&W fixed a couple of them without a problem. The only firearm that I am not sure that they will repair is any LEO trade in. I own an LEO 5906 trade in and have not had any issues with it.

Have you checked the flow rate of the gas tube? Could have a blockage, sounds like the rifle is short stroking which leads one to suspect it's under gassed, and if you have the original pinned FSB has block it can't have moved so a blockage seems the next most likely cause seeing as you already eliminated leaks and tried a different BCG

I'd probably also put in a new buffer spring seeing as they are cheap, just to eliminate the chances of it being that, but don't think that would cause the symptoms you describe.

Yes I have tried new buff spring and cleaned the gas tube out. I have seriously tried everything and I'm throwing in the towel! Hopefully S&W will fix it. I love the gun it's just so frustrating back and forth to my range...thanks guys