In F-TR, you can choose to shoot a .223 rather than a .308 but it requires a fast twist once you get past 500yds. In the distant past at Roy's hill, I shot a few possibles with light projectiles out of my slow-twist 700VS at 500 but they got murdered in the wind at 600. 1000 is DEF out of the question Neil.
If you changed to a fast twist 28"+ bbl and shot 77-80 grainers, you could have a play at 1000 but it wouldn't be very competitive. Stu would still be caning your butt..
Just for an experiment, you could try some 53 VMax at our next 600yd shoot. They have one of the best BCs in their weight class
Bookmarks