The only way to do it is a pain.
You have to get the weapon registered to your Armory. As long as it's on the count you can take it over and bring it back. Your best bet to do this is to talk to the NCOIC of your Armory. It's not going to be the same paperwork as checking your weapon into the Armory. So make sure it's the right paperwork you sign. The later will get your weapon in a no go status on the trip back.
However be warned. That in a fire fight should the need arise to trade a magazine with someone you will be screwing yourself or the man next to you.
I will say that nothing stops a threat like a .45
Keep your eyes open and your head on a swivel.
If you get a funny feeling in your gut, trust it!