Great choice on the 50776, that is at the top of my short list. The other one on my list is the 51411.
I do like 18.5 inch barrels and 7 shot capacity from the factory makes it even better. Would have a 14 inch barrel if it was legal!
My TR 500 came with a tri rail and it had to go, just not for me. Got a Hogue off of eBay and I really like the feel. Never tried the Magpul but that should work great.
Thought about changing the stock for a Hogue overmolded, but really have no problem with the 12 inch LOP that came on the TR 500.
Let us know how that bad boy shoots.