Let me ask you another question guys. How does that 516$ rifle compare to the m&p 15? Would it be worth it to build it myself or would it still be an inferior product compared to the M&P?
Depends on what
you like/want. The one you can build for about the same price as the M&P will have a forward assist & dust cover, and it will also sport your choice of buttstock, and the upgraded Magpul grip and hand guard. To me, it's a no-brainer. But I personally cannot stand M4 stocks, A2 grips and A2 handguards. They're ugly and uncomfortable.
However, if having the S&W warranty is a big deal to you, then that's a factor to consider. But do remember that the AR-15 is a very easily serviced weapon, every part replaceable at home with just some basic tools and an armorer's wrench.
Quality wise, I'd pit anything PSA is putting out under the PTAC or Freedom labels against the M&P Sport parts. The PSA premiums are a step up. All the PSA stuff is up to spec, with 7075-T6 receiver forgings, 4150 CMV or 416 stainless barrels w/M4 ramps, 8620 steel M16 bolt carriers with 158 carpenter steel bolts, etc.
This is the PTAC 1:7 stainless MOE upper, PSA MOE lower build kit & PSA bolt carrier group/charging handle combo I put together this last Friday on an Ares Armor 80% billet lower I finished out a couple weeks back. I'm into it for $546 after shipping:
Tell me that doesn't look a whole lot nicer than the M&P Sport. I can tell
you that it definitely shoots nicer.
If you decide to sell later the Bargain basement SW will likely be easier to sell and bring more than a bargain basement home build.
That's conjecture. ARs really
are the sum of their parts, and their is no second hand warranty, so that becomes a moot point on the used market. I am positive I could resell a Magpulled-out PSA build for more than an M&P Sport or DPMS Oracle.