The Siamese is a modified M98 mauser isn't it? Therefore it has a mag capacity length of 3.115 to 3.31" depending... The 45-90 Win has a case length of 2.4 and COAL of ~2.90" to whatever you want to seat the bullet at. There is also the 45-110 Sharps Straight or 27/8" that could be use or trimmed to give you a max mag length of 3.30" fairly easily.
I converted a SMLE 2a 308 Isapore to 458 American and can shoot 45-70 to 45-100 case lengths but at a max COAL of ~3.06 due to the constraints of the SMLE mag...I also use a 458 WM case cut to ~2.3" to get the COAL I want for crimping in the cannelure of the bullet I happen to be shooting. I actually used a 458 WM reamer but marked the barrel 458 American for safety sake.
If it were my rig I would just rechamber to 45-100 and load to whatever COAL the mag allows and call it good...keeping the pressure within the strength of the receiver. I would ALSO the headspace and then maybe just rechamber to the belted mag case just like I did with my SMLE...the headspace should be around 0.060" and if you chamber right BOTH the belted mag AND 45-70 to 45-10 cases can be used. With the SMLE 2a 308, 12 round magazine I can feed a couple of rimmed cases from the top, then 458 Am below that.
I load only to ~45KCUP, because that is the receiver's spec, right at 2000fs with AA2460 and 450gr hard cast bullets, but with a M98 you should be able to go a bit faster, safely. I like the 450 gr bullets as a good compromise between a "standard" 400 gr and a "heavy hitter" 500 gr. TrueShot 435 gr is another very good, unbelievablely uniform as to diameter and weight bullet that shoots very well ~2150fs and would definitely go faster in a M98.
You would be in the 458 WM range of ballistics with a 45-100 case as my 45-2.6" measures 2.6"(DUH
), or near Lott with the 45-110 Sharps Straight.
I wouldn't mind finding a "cheap" Siamese floating around loose...I can always use another toy to play with. Hahahahaha
Hey...that ol' grampa cartridge will eat your lunch if it is loaded in a modern receiver at modern pressures...I garoontee, MON CHER.
Lots of ways to jump here.
LUCK
