Kimber 84M Montana Rebarrel, 6 CM or 243 AI?

[Tanner]

I’ve got a handy little Montana 6.5 CM cut to 16” that shoots pretty well, but seeing as it’s winter and I can never leave well enough alone, I’m thinking about a rebarrel to a 6mm cartridge for use as an all around backpacking rifle.

I’ve got a 6.5x47 and a 6 Creed already so I’ll have some overlap regardless, but ideally I’d like to shoot 115 DTACs in this Montana, and get them close to 3,000fps. I know the Creed won’t get there in an 18” barrel, as mine shoots them at 2830 via a 19”. You folks shooting 243 AI’s these days, please chime in with what you’re seeing for velocity’s…. It’s been 10+ years since I owned one and I was shooting 105 BTHPs at 3150, in a 24” Shilen.

I wouldn’t mind having a different cartridge here as to not have to keep brass separate between 2 different chambers.

For what it’s worth, this rifle will be cut to a max of 18” and likely be a 1-7.5” Lilja in their Montana dupe contour.

 

[pods8 (Rugged Stitching)]

What cartridges length does the Montana accommodate? IE would 6-284 fit? That’d give you a velocity bump over the creed while still maybe fitting the action length and standard bolt face.

 

[Tanner]

What cartridges length does the Montana accommodate? IE would 6-284 fit? That’d give you a velocity bump over the creed while still maybe fitting the action length and standard bolt face.

I’d love to do a 6-284 but the 84M only allows 2.82” max COAL, think a guy would need an 84L to make use of the 284 case.

 

[PathFinder]

My 243 AI is a 20" Tikka with the throat cut for the 115 DTAC to jump .060" with the boatail at the neck/shoulder junction. 2950 with H1000 is a pretty reasonable load (48.5 grains) in Alpha brass. There's probably more velocity to be had with RL23, N565 or N560. I pushed it all the way up to 51 grains and 3075 fps, but that was leaving an ejector mark on Alpha brass so probably pretty hot.
COAL is longer than 2.82", I'll have to measure and see exactly what they come out to.