A good expanding SP or JHP would make an M1 Carbine a very good defensive weapon, since the ballistics of the .30 M1 are similar to .357 Magnum from a rifle. However, you need to ensure that your Carbine will reliably feed your chosen load.
E.g., last year MidwayUSA had a good deal on Magtech .30 Carbine JSP, so I picked up a couple of boxes to test in my Underwood. I had several failures to feed in the 1 50-round box which I tried so far. The same day, I ran ~100 rounds of GI Ball made by Remington in the early 1950s. The Ball was noticeably hotter and function was 100%.
The other factor is whether or not a JSP or JHP actually expands. You'd think that a JSP at M1 Carbine velocities would reliably expand, but I've read that Federal JSPs don't do so reliably (anyone with contrary experience please correct me).
Winchester makes a JHSP (jacketed hollow soft point) which by the looks of it, should expand. I plan to test some in my Carbine and would be interested to hear from anyone who has tested it for expansion.