Why don't you just use a .30 carbine? Cheaper reamer, cheaper brass, readily available bullets.
Already quite common 6mm/223. Quite a few Mini's converted to it.
6 x 45mm looks like a perfectly fine cartridge and very accurate, but it's about 2800 fps. I think I'm going to go with the whisper, a subsonic round, for the novelty and variety of it, plus......it's subsonic, and that really appeals to me. A typical loading only loses about 70fps between the muzzle and the target at 200 yards.
There are alot of good 6mm bullets out, especially now that the 6mm benchrest is so popular, but for availability, I think .30 caliber still has a definite advantage. Also, with subsonic.... I'll be able to use cast lead bullets, without adding too much antimony, and maybe without even using gas checks. That will be new for me!
I might be less interested in a subsonic loading if I lived in the mountains or the praries, but I live in northern ontario, and where I shoot, we're surrounded by dense bush, and high berms on my range. There's no wind most of the time, and I often am the only person there. Most of the members only show up to sight in their rifles for hunting season, and there's only about 150, all told. It would be really nice to shoot with just a little cotton in my ears instead of both plugs and muffs.
The term ".300 whisper" is trademarked, but the .30-221 isn't, and is the same cartridge. Shilen makes ready to install barrels chambered in it, for savage rifles; fireball brass is already as cheap or cheaper than the hornet brass I go through, and dies are available.
Nope, I think the whisper is the ideal large and slow loading on this switchbarrel project, for me.
Also; can you imagine how long a stainless shilen bull barrel will last, never pushing those .30 caliber pills more than 1100 fps? I expect to see pistol barrel type longevity...
