Hi
Got a question for you knowledgeable folks. I have a Bushmaster with a 20" HBar on an A2 receiver and I was wondering what it would take to swap it out to a flat-top (A4) for scope mounted varmint shooting and long range stuff. Estimated costs and ideas as far as receiver make and if there is anyone able to perform this sort of work near St. Louis information appreciated.
Thanks in advance !  Merry Christmas !!

~$100 for a stripped flattop upper receiver and transfer over all the little parts or spend $20-30 more for new uper parts.  

Tools needed to do it yourself:  Small hammer, pin punches, electrical tape (to protect surrounding finish when tapping in the pins), barrel nut wrench ($20), a "vise block" ($several bucks) and I think that's about it.

Check out what's for sale in the "New Upper parts" section in the EE.