I built one on a Stiller Tac 30 with McMillan A3, Krieger 1-12 twist barrel, jewel trigger. Originally it was 24" but cut it back to 18" when my suppressor came along.
I personally went with 1-12" twist because that will get you to the 85's and where I feel the 6x45 shines is in the 65-80gr bullet range. I've got several other rifles in 6mm and if I need a heavier high BC bullet, there are better power plant options for heavies out there than the little 223 case.
However, for your shooting pleasure inside say 500 yards on somewhat calm days, there is nothing much more fun or cheaper than the 6x45. I had one in an AR too and liked the chambering enough to go full tilt on the build. If you like it in the AR it only gets twice better in the bolt gun.
-get the bullet out of the case for more powder capacity (no more 2.26" handicap)
-Get the bullet near the lands (no more 2.26" handicap that keeps anything more pointy than a shoe box in a "jump" even with a zero freebore) for better accuracy **** the best of all advantages
-Better bullet options (no more 2.26" limit, opens doors to bullets like the Berger 69gr HBCHP and it's slender design that is too deep in the case at 2.26")
-Stop having to look on the ground for brass
-Bolt guns in 6x45 are just cool
-Bolt guns in 6x45 make your friends jealous & then they build one too
It's cheap to shoot (almost free brass with little powder charge), has little recoil & pop (especially "canned") & barrel should be good for several thousand rounds. ANd the more you shoot, the better you are. So it makes a lot of sense... Especially when it shoots like it does. It's "almost" as good as the 6BR on paper, even using range brass...