What is the maximum chamber pressure for a M1 (30 cal. ), I want to build a wildcat M1 in a .357 Mag. cal.and would like to get the spec's for safety reasons.
Check Handloads.com or one of reloading manuals. I think SAAMI pressure for 30 carbine is 40,000, but check.
Not sure you would gain anything by converting a carbine to .357. Milspec 30 carbine ammo (110 gr @ 1955 fps +/-) meets or exceeds .357 mag energy when the .357 is fired from a handgun. For energy transfer try using soft point ammo instead of FMJ. Soft points feed like FMJs and have less tendency to pass through than FMJs.
Also, you'd have to find a barrel with the correct bore size. There are some replacement barrels for carbines, but they are all in 30 carbine. Not sure I'd want to rechamber and bore out an old carbine barrel to a greater diameter. Not sure how that would affect the safe pressure level of the chamber.