Hey Bill, I'm gonna address 6x45.
1. 6x45 is a great caliber for AR's & bolts in states that require .243caliber for deer. 55gr up to 95gr in an AR, and over 100gr in a bolt. Def not a 1000yd round. But a round that is gaining in popularity due to extremely cheap brass and bullets.
2. Its a barrel swap and go.