My truck gun is a .243 ( Remington 700) put together from parts. 21" barrel HS precision stock and various sourced factory remington parts. with 6x Weaver it weighs under 8 lbs. and with three main loads will kill bunnies to eat up to deer sized gun.
Loads:
55 gr Nosler Shots bullet Loaded to 2400fps with Unique
55 Gr Nos. Varmagedeon HP with IMR 8208 to 4000fps
95 gr Berger VLD with RL -17 3175fps.

These three loads cover all I ever need from a truck gun and more. Only bad thing is the Varmagedeon load is very destructive on fur or edibles.
But a Kimber( your choice) in 243 is a good choice.