6.5mm Grendel. Wow, I am impressed.
I was out at the range the other day and shot an Alexander Arms AR chambered in 6.5 Grendel. The Grendel is essentially a 6mm BR necked up to 6.5mm. I was shooting 120gr Sierra MatchKings and holding under 1" at 200 yards. It was running better than 2500fps and was an absolute joy to shoot.
I think with an appropriate twist rate to stabilize the 140gr SMK's this would be a great varmint caliber.
Just thought I'd share my experience. There is a good article on the caliber at http://www.65grendel.com/
I also shot a .50 Beowulf, it was fun but definitely not long range material. Would be great bear/hog medicine though.
If some is good and more is better, then too much is just right.
My mind is a raging torrent, flooded with rivulets of thought, cascading into a waterfall of creative alternatives