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Your 6x45 with a suppressor will gain both velocity and accuracy. I use a Sonic 35, I can remove baffles for the 6x45, and add them for the 243AI, so it isn't too heavy on the light 6x45.

Give...

2750fps with an 85gn bullet from an 18" barrel is about the best you can get I think. You might get a tinch more with a suppressor. I guess the faster powder you can get is what you need.
I have a...