I have used the following cartridges and calibers for long range varminting, long range being 400 to 1000 yards. I have used .223, 22-250, 220Swift, 243AI, 6MMAI and 6x284. All of the cartridges and calibers I mentioned were all used with fast twist barrels for long bullets. If you noticed, I did not include the 6BR in the cartridge list. The reason, my dumb butt never owned one. All it took was one day of shooting varmints with a friends custom 6BR, and I was hooked. For small varmints like Pdogs and Squirrels, the 6BR is a perfect long range varmint cartridge out to 1000 yards. With the right bullet, 105grn A-Max, 105grn Berger VLD, Lapua 105grn Scenar or Sierra 107grn MK it is super accurate and has plenty of energy to kill a Pdog or squirrel at a 1000. If your going to shoot bigger varmints, like Groundhogs or Coyotes out to 1000 yards, than I would look at the 6x47 Lapua. However, for small varmints from 0 to 1000 yards, the 6BR is king in my book and that's why I am finally having one built. So my vote would be for a 6BR with a 1-8 twist barrel with a 236 bore. The 1-8 twist will allow you to shoot anything from 55 to 107grn bullets. If you go with a slower twist, like 12 or 14, you will only be able to shoot the lighter bullets and those bullets will not help in the long range department. Another excellent attribute about the 6BR is the Lapua 6BR Brass. It is as close to perfect as you can get. The 6BR Lapua brass allows you to have a Match Chamber and no-turn .272 neck that requires no turning at all. A loaded 6BR round, with Lapua 6BR Brass, measures .270, that allows for .002 clearance. That's basically a tight neck chamber without the turning. I have had my share of turning necks, and I most say I am sick of it. The 6x47 Lapua would be a good cartridge, but I am going to stick with the 6BR this time around. I am building a full custom this time, so I am looking forward to taking this one on the hunts next year. Once again, my vote is for the 6BR. Good luck and have fun.