Which Chambering for a Straight-Pull Guide Gun?

[barnbwt]

I'm trying to decide on which cartridge I'd like to try rechambering a Steyr M95 to,
but I'm a bit at a loss as to which direction I should take. I wish to end up with a straight-pull bolt-action guide-gun. The actions of these rifles have been successfully chambered in 8x57 Mauser, and the 8x56R Nazi surplus mine shot was over 51000psi if I recall--so the action appears stout enough for anything up to (but not including) full-on 458 Win magnum.

I'm new to large bores (my largest other caliber is 30-06) so I only have a modest familiarity with the various cartridges/families of this realm, and even less idea of their performance and uses relative to eachother. Hopefully, some of ya'll will weigh in on which you like (and why). Belted vs. rimmed, etc.

My only requirement is that the cases be straight-wall, or very near it (with no neck) since I've come to realize I shoot easily reloaded cases a lot more often . I'd also prefer something commonly available (not from Wal-Mart, but just not some boutique wildcat) or stupid-simple to form from another common case. I came up with several candidates below vying for the nomination; please suggest others you feel have similar attributes, as well.

My size envelope limits are:
-.608" Rim/base diameter same as 45/70 or smaller (and that's pushing it)
-Overall length 3.228 (8mm Mauser fits) and perhaps a tad longer

In ascending order (I think) of power level:
.444 Marlin** (I'm aiming for power well above most pistol rounds)
.454 Casull (probably too short to feed right)
.460 S&W
.450 Marlin*
.45-70 (the .602" rim of this is probably as big as can possibly fit on the bolt face)
.458 Win Mag* (Loaded-down to sub-SAAMI specs to stay below present bolt-loads. This guy may also be too long to fit with heavy rounds)

*the M95 is designed to feed rimmed cases from an en-bloc clip (for now). With the possible exception of 444, I will need to replace the magazine system and modify the extractor quite a bit. I'd prefer a sturdier solution to the current feed system, so rimmed/non-rimmed is a non-issue, unless one is more reliable than the other (in both feeding and chambering)
**I've seen firsthand accounts of folks successfully doing this in 444, & heard of it being done in 45-70. 444 requires little other work than a new barrel, supposedly, but is the least "fun" of the candidates

SO, which do ya'll prefer?
I suppose I could start with the smallest-volume round and work my way up in my rechamberings; that way I could stop once I find the right cartridge . Removing metal's easier than adding it, no? I'll have enough pennies in the jar in ~2 weeks to buy a barrel, so I need to get my ducks in a row now

TCB

 

[RPRNY]

Not on your list, I suppose because you have already discounted them but thought I would throw them out:

8mm Rem Mag. Too long? 3.65" OAL, and/or to much pressure 65,000 psi?
.325 WSM - length is okay but again, 65,000 psi
8x68 s (or RS for a rimmed version) which should fit for length as it was made to be chambered in the Gewehr 98 and is slightly lower pressure at 63,000 psi. This would be a cartridge contemporaneous with the rifle as well.
And finally, 9.3x62 Mauser, the great German African cartridge. Will fit for length at 3.29" and at 55,000 psi should be okay for your rifle. This is a classic and ideal for your project.

Not sure I understand the issue with loading for a bottleneck cartridge? Reloading for bottleneck rifle cartridges is pretty straightforward...

From your list however, I would go with 45-70 if you can make it work. It meets your other criteria, can be loaded to various levels, is a widely available factory ammo, has plenty of punch and is "guide gun" material.

 

[Gordon]

9.3x62 would certainly be my recommendation.The 286 grain 9.3 bullets are fantastic at 2200-2400 fps ,maybe better than .375 H&H, almost.