Shooting in prone position with bipods,it's not unusual to "cloverleaf" 3 shots into the same hole at 100 yds.I've shot Remington ammo,black hills,UPC,federal,and some Ultramax i got from sportsmans guide.I haven't really noticed a huge difference in any of them,but I prefer the rem. Varmint loads,since I mostly use it for hunting groundhogs.I had really good luck with the blackhills too for the price.
I usually shoot a 52-55 grn bullet,and I think the rate of twist is 1 in 28,but I can't remember for sure.I'll have to look in my owners manual to see if it says and get back to you.