I am getting things together to do a Lee Speed type gun on the Australian #1. I am aware the #4 is stronger but I am wondering about the #1 as I prefer the esthetics of the #1. Darryl stated that the # 4 was 55,000 PSI capable and would work fine with the 45-90. I have been checking pressure number on some cartridges and came up with a load behind a 400 grain bullet that gives 1926 feet per second at 28,000 PSI( This is in a 45-70). This develops 3295 pounds of muzzle energy. Assuming these facts are correct, the # 1 should handle this with no problems. The reason I was interested in the 45-90(if the case will fit) is because I wondered if the larger case would develop less pressure. I went back to Taylor and found that the 450 3 1/4 developed 17 tons of pressure and the 450 3 1/2 developed 13 tons. If these numbers are correct, then the longer case developes less pressure. If the 45-90 will fit, will the longer case reduce pressure in the # 1 ??. I am not trying to make a 458 out of this (and no, I would not take a 45-70 after anything in Africa at any time and any place). Also, I was wondering if the 35 Winchester would fit this action as the cartridge is shorter than the 405. Anyone have any experience with the 375 JDJ which is based on the 444 Marlin ??