You can go to benchrest.com and look at the ads by the major barrel makers and installers. You don't say "how big." That 17 is not a small, light action. Great for magnums. .243? No recoil felt... The big names have a wait. (Surprise.) Hope you weren't thinking of yesterday...
To tell the truth I'm still deciding on caliber. Based on some recommendations I've had I decided against chambering it for a magnum. Not so much for pressure reasons, but rather I heard from many that it was just difficult to get it setup in such a way that the cartridges feed reliably.
With that in mind I've been waffling around, but the 3 that I'm thinking about are 6.5x55, .35 Whelan, or 9.3x62mm.
I had a 6.5x55 M96 Swedish sporter once upon a time. I liked the round, but the rifle just wasn't as accurate as I'd like (2.5" - 3" groups at 100), and I hated the pressure restrictions of the small ring Mauser when it came to handloading. I sold the rifle a while back and told myself I'd get another. Benefits there is that I have 2 die sets, brass, and plenty of bullets still left over since I fully plan to get another 6.5x55 before too long. I've already got the .257 Roberts though which is close-ish in performance, so it's not like I'm filling a hole in my arsenal.
.35 Whelan or 9.3x62 would be nice too. I have sporting rifles in 8mm Mauser and .30-06, but nothing bigger than that, so a medium bore thumper would be nice if I ever take a hunting trip that needs it, but normally the biggest things I hunt are whitetail (about 200 lbs max) and feral hogs (about 350 lbs max). Also, ammo prices for either of these is higher - particularly for 9.3x62.
No hurry on it though. I've been piecing this thing together for a long while now. I've got other rifles to hunt and shoot with
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