A P229R is chambered for .40. It’s also less of a pain to carry around than an M14 or a M240, which is a machine gun anyway.
And a M104 is not nearly subtle enough.
My eyes are on a .40 Baretta Storm.
Hmmm. What if I said 9mm to see if you were on your toes?
;)
(I think it's also available in .357 Sig. but I don't blow holes in things as often as you you do, nor does Uncle Sam pay me to do it. Thanks for your service.)