1. Have a gun in your inventory with nothing in your hands and that gun hot keyed.
2. drag ammo to gun and reload it.
3. as the reloading animation is playing press the red "X" on the top right of the "in hands" box.
4. quickly close the inventory screen and spam the hot key that is assigned to that gun from before to right after the animation is finished.
5.
a. you can press g and and have someone take the 2nd gun (this sometimes doesnt work) or
b. when done spamming, re-log and press g right as you log in and you should have a gun on your back and a gun on the ground.