Have no idea what it will do to accuracy , probally nothing. Kick, well if it's light, it will kick more. Velocity, you cut off 6" of any barrel and you lose velocity. A guess off the top of my head, I'd say you effectively taken a 300 weatherby and turned it into a 30-06 with a huge amount of muzzel flash.
I agree, at least not enough vel. difference to justify the round.
Fast powder will help, but not enough.
As Drilling Man stated, the Wea. was designed for a 26" tube & they still work pretty good with a 24". Concerning the brake, remember that the
blast will increase even more with a brake being screwed onto a 20" barrel as opposed to the 24". Yes, hearing protection is vital & if you shoot it
once even while hunting with a brake on this 20"& no protection, you will pay, I promise!! If you got a good deal on this gun, I would either sell it
or have a 26" or longer Lilja installed. If you want a 300Wea. you might as well get the Wea. performance.