I think the best fix is to make feeding better and make a tremendous combination ist o set them up as a 45-90.
The extra length should make them feed better.And 458
WIN power is possible.Simple reamer job.Ed.

I had one years ago. (Trying to buy it back.) Mine was converted by Shaw, but I sent in the action and think the barrel was 20" or 22". Never had feeding problems and the gun would take a lot hotter loads than my shoulder would.

Burned most of jug of 5744 through it, but I forget the charge.

From what I've gathered, a 500gr bullet (+/- a few grains) is the optimal Gas Checked CAST bullet (RN or Potsell design, not Flat point, for feeding issues) for the twist and a 350gr bullet weight in a JACKETED design is the optimal bullet weight (1 in 18" twist, 24" barrel). Correct?

Also, if I decide to 'do it right' with the action/caliber, a 45-90 or 450 Alaskan chamber change (I'm leaning toward the latter, personal choice) and also to mill out the rear action port for ejection issues. Correct?

Thanks

I had a .45-70 Siamese Mauser for awhile. It was quite accurate with 350-grain Hornady RNs at around 1700 fps, but like others have said, it had occasional failures to feed. I've gotten rid of it in favor of a Guide Gun for .45-70 loads at 1700 fps and a Whitworth .458 WM downloaded to 2150 fps or thereabouts if I have need for a .450 Marlin equivalent.

All of the Siamese Mausers I've seen in 45-70 would either fail to feed or eject in one form or another. The 450 Alaskan which is based on the .348 win case is much better suited to this action than the 45-70. Because of the rim, the mag of a Siamese Mauser is designed to stagger the cartridges and frankly, I don't think a 45-90 will even fit in the mag. I'd bet the feeding problems would be even worse. I have done a .405 win on a Siamese Mauser that worked out pretty well FYI. Most of the guys who own these things tend to push them. The Siamese Mauser like all 98's was designed for 45Kpsi cartridges and will set back the locking lugs on a steady diet of 60-65Kpsi loads. I've never heard of one blowing up though and as a Kid I tried to once blow up a Siamese Mauser witha full case of bulleseye fired with a long string. As others have reported, the action held. the brass vaporized and the extractor departed the planet, but the action did not fragment like a 1917 Enfield or 1917 M98 Mauser did.-Rob

Changing mag single stack will make it feed.If it couldn't
be demolished by bullseye, I wouldn't be afraid doing one
in 458Win. They have been done in the 2 in version call 458
American.They been done in 7.62 x 54 Russian also which is
50 k psi pressure.Bolt lugs are as bigger than on 98s and has the same stile safety lug..Ed.