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Ghostwall, or anything that don't disconnect you from the servers while lagging.

This is a pretty useful glitch, especially for snipers.

We will assume that you would be on a hiding spot, where you are pretty far away from a resupply box location.

1) Kill enemies.
2) When you have no ammo left, flip your switch.
3) Run to a re-supply box location and restock your ammo.
4) Unflip your switch.
5) Ta-da. You'll be teleported back to your previous location where you flipped your switch, with full ammo!

This is a lot faster than going to re-stock your ammo and going back to your hiding spot.

Re-stocking ammo or getting weapons from dead bodies are all client-sided, apparently!