Steps:
1. Group up with another player.
2. Acquire a two-handed weapon.
2. Find another two-handed weapon.
3. Put the gun you have on your back and pick up the new into your hands..
4. crouch and press spacebar to raise the weapon.
5. Log out and the other player will notice the gun in hand drop to the ground.
6. Have the other player pick up the weapon.
7. The player who logged out, log back in (easier to log in a steam friend through the message system).
8. Notice you still have gun in hand and the other player has the one that was dropped.