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I think so. A lot of the LARPing gun people who would claim it's OPTIMAL to do one or the other aren't factoring in the fact that you don't know when you have to reload or not. No popup saying out of ammo, right? So in a situation where youhave a rifle you're holding empty, you hear it click, what does your brain do? Maybe you drop it and draw a sidearm, maybe you have trained to put in a fresh mag quickly.
seems like the military would figure out which one is most optimal and then train that way.
from what I gather on quora switching to sidearm is easier because it requires less hand-eye coordination and fine motor control. Reloading you must eject the magazine, retrieve another, then insert it, and requires both hands. Sidearm you just drop the rifle and then pull out pistol with one hand.