I don't have the 6X45 but I run the 6X47 based of the .222 Rem Mag case. I'm able to push a 70 grain bullet at 3066 fps pretty easily out of a 20" barrel. I killed a pronghorn buck at 300 yards two years ago with a 70 grain Nosler ballistic tip bullet. At longer ranges a varmint bullet will hold together pretty well. My problem is though I wouldn't use the bullet at close range as I wouldn't trust it enough to make good penetration. I've been in a search for a little tougher bullet and I think I may have found it.

While digging through my stash of 6mm bullets the other day I found a partial box of 85 grain Sierra Game Kings. I've searched for reviews on this bullet and it seems to be pretty tough and holds up well even with MV's above 3000 fps from .243 and 6mm Rem rifles. I used a 1:12 twist barrel for my build and if I was to do it over again I'd probably go at least a 1:10 but then I might not be able to get the velocity I'm getting. These bullets should stabalize from my barrel as well because they are nearly the same length as the 70 grain NBT my rifle likes. I'm hoping for a 2800 fps out of the Sierra as that will get me above 1000 ft-lbs of energy at 100 yards, which will keep me legal with Colorado's big game regulations.

I've had great results with 55-70 grain bullets by Nosler and Sierra finding groups easily going under 1/2 moa if I can pull the trigger right with speeds up to 3300 fps. I couldn't get 80 grain Remington or Winchester bulk bullets to shoot better than MOA at 100 yards. I haven't tried any of the 80 grain Speer's yet, but realisticly at the speeds you are going to push bullets I doubt you'll really need to use 95-100 grain bullets on game. With bullets of 85 grains or less and especially if you use flat base bullets I doubt you'll have any magazine length issues.

My build:

Stevens 200 centerfeed rifle
6X47 Rem chambered Sin-Arms 20" #3 contour chrome moly barrel with 11 degree target crown
SSS Competition Trigger
SSS Recoil Lug
SSS Bolt Handle
Savage metal trigger guard
Leupold VX-II 4-12X40AO fine duplex (Burris 2-7X35 ballistic plex pictured, what I had before I got the Leupold)








Typical groups with the rifle 70 grain NBT and Sierrak BK:




Best group with Winchester 80 grain PP:




Sorry for the long post!