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.
In reference to your concern about the chamber pressure level above it's approximately 40,000 PSI see below:
The Following Data extracted from TM 9-1276 Cal. .30 Carbines M1, M1A1, M2, M3, U.S. Government Printing Office, 1953 (paragraph 6, pages 8 & 9)
M1 M2 T3 M1A1
Number of Parts* Early: 56-58
Late: 55-56 64-65 Early: 79-81
Barrel Length 18"
Sight Radius 21.5" @ 100 yards
Overall Length 35.58" 35.63"
Overall Length-stock folded 25.51"
Weight 5.5 lbs 6.19 lbs
Trigger Pull 4.5-7 lbs
Rate of Fire (full auto) 750-775 rpm
Stock Material WWII walnut, some birch, a few cherry walnut
Stock Material post WWII walnut, birch, others walnut
*number of parts varied as minor changes were implemented and do not include a
complete breakdown of the rear sight and barrel band
.30 Carbine Ball Ammo (GI)
Weight of Bullet (aprx) 111 grains
Weight of Loaded 15 round mag .59 lbs
Weight of Loaded 30 round mag 1.07 lbs
Weight of 100 Cartridges 2.8 lbs
Muzzle Velocity (aprx) 1900-2000 fps
Chamber Pressure per sq inch (aprx) 40,000 lb
Effective Range 300 yards