one other thing to think about, the osprey kit is about $100 more than other kits that i have checked into.$100 may not seem like a lot to you, but it is for me!
I have seen them for 319.00. And that comes with the bolt carrier. I haven't looked at the the other kits as I had this one already and wanted to use it. I am not trying to sale the kits just telling people about my experience with them.