If you have auto-reload turned on and you fire the LAST bullet in your MOA/FEL-IX magazine, the game prevents you from switching to your sidearm or knife for around half a second.
This may not seem like much, but it’s a SERIOUS pain in the ass when I tag someone with my sniper and then want to finish them off with my machine pistol but I can’t switch in time and my opponent kills me before I can put the final 1 or 2 bullets into them.
I’m pretty sure that this doesn’t happen with most other guns in the game, but not 100%.