Dusty,
Your load would certainly dispatch them humanely, however I'm guessing there wouldn't be much meat left. That sounds more like a varmint round to me.
I don't know if I would use a FMJ for small game, at least not a spitzer. You could probably get away with a roundnose or flat point .30-30 bullet.
I've been working up a load with a single buckshot for my .357magnum lever action. I used black powder which will suit me fine, but I think I'll also try to find a smokeless load too.
A .30 caliber ball will weigh about like a .22 slug, something in the neighborhood of 35 to 44 grains. I just feel better using something light for squirrels as you are generally shooting skyward which is a big no-no for any other rifle. Plus the balls are so aerodynamically poor that they behave like a flu-flu arrow where they come out fast, but slow down really quick, so they won't even go the mile that a .22 supposedly can.