Re: Which Caliber???
I'd go with a 6mm in one form or another. The smaller the case the tighter the groups seem to be - 6br or 6ppc. The larger the case the better the splat.
The old 243 would be a sweet compromise. Need more splat? The 243wssm is a screamer and surprisingly accurate.
My pick was the 243. 87vmax a shade under 3200fps. The first shot opportunity was a big jack under thirty yards. You couldn't find a piece big enough to identify as rabbit.
A few days later a friend and I were parked on the edge of a long valley. The valley was covered in snow, thin grass, and thin sage. We shot jacks from fifty yards to 550 yards. It was amusing. They made quite smear on the snow. Seemed every time we shot one two more would hop up to sniff it. Pop, giggle, pop, giggle.
For even more splat you could run the 58vmax at 3800.