If I was going for a Semiautomatics Pistol Caliber Carbine it would be a 50AE.
I really dont see the reason for a 357 sig over a 357 magnum if they where both semiautomatics (like the Desert Eagle).
"I ask, Sir, What is the militia?" "Its the whole of the people. To disarm the people is the best and most effectual way to enslave them" -George Mason Co-Author of the second amendment.