Re: twist rate for a 450 bushmaster
I see 2 questions that need to be answered above.
1) Twist rate obviously
2) How are you going to get the chamber cut?
Let's address #2 first.
You can take a barrel from an 450 Bushy AR and stuff it onto the nose of the FN action. You most likely will need the reamer to clean up things while the barrel is being headspaced to the action. This assumes the threads are the same, which I doubt.
So, you really need to chop the threads off and rechamber it. You need the reamer this way as well.
You're going to need to find a 'smith with one already (which is probably going to be very difficult since it's such a new, proprietary caliber). This probably means you're going to be on the phone with PTG or Clymer to get a reamer, or if your gunsmith is willing to do it, make a reamer himself.
This leads me back to #1
Since you need a reamer either way, and a barrel straight from Bushmaster is not likely to be cheap, I'd suggest a fast twist blank in the contour you want from someone like Adams and Bennett. They're cheap barrels, but for what this caliber is capable of and being used for, it's more than acceptable accuracy grade.
Get the faster twist barrel in a 1:16-1:20
