lots to consider. I shoot an Eliseo Tube gun with a R700 clone action by Bordon and an 8 twist kreiger medium Palma barrel of 29" in 260 Remington from the sling. It shoots much better than I do at both 600 and 1000 yds. If you can keep the barrel length near 30" you will still be able to keep the projectiles supersonic at 1000 yds (this is really critical). You have to keep the projectiles moving at about mach 1.2 at 1000 to maintain stability. A longer tube will allow you to keep your loads moderate thus saving wear on you and the rifle. Anything less than 28" is going to handicap you as the loss in velocity can make bullet selection a serious issue. Make sure your smith understands the needs of a long range shooter as a R700 action, while a good start, really needs some tweaking to perform well at 1000. Caliber selection can be an major issue. The 6.5/284 while a great long range caliber, has a limited barrel life. The 6.5 Creedmoore , the 6.5x 47 Lapua andthe 260 Rem all will perform similarly. I chose the 260 because of the easy availability of Lapua brass and additional available data.
Check out this forum and don't be afraid to ask questions. They are a great bunch of guys with tons of Long Range experience:
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