Other than cpacity are there any differences between the first 3 side arms on COD 4?

May be...

I know the deagle is more powerful but between:

-USP .45

-M1911 .45

-M9

What is the difference [i know M9 has higher capacity]

i dont think there is much differrence

but from experience i would have to say that the M9 would probably kill better than the rest

the desert eagle will still lay waste to all of them tho