Re: long range groundhog rifle
I have both a 6BR and 6x47 Lapua. The BR is a single shot so I can't claim to know if it feeds, but I've heard they can be made to feed by a competent 'smith. The 6x47 is built on a 700 BDL short action and it feeds flawlessly. Really not a whole lot of difference between the 6x47 and the 243. I have and shoot both and a 100 fps difference is hard to see. Theoretically, the 6x47 should be more accurate, because it's a custom barrel, but my 700VLS in 243 thinks it's a custom. If I had to do over, I wouldn't have gone 6x47, since my 243 is basically the same thing. The 6x47 has more cost in dies and brass they can be tough to find. The 243AI, 6mm or 6mmAI in a fast (8) twist would be a great choice. More HP than the others.
There are also some other 6mm variants, such as the 6XC, 6BRDX, etc. that are being used by long range guys. Again, you get into the more expensive die and brass issues.