Im going to show you how to lower your weapon in Halo reach
Step 1: Make sure your network is offline
Step 2: Get in any game that does not involve being online
Step 3:Hold these buttons - X, B, right thumb stick, and down on the D-pad. Hold all those buttons for at least 3 seconds and your weapon is lowered.
Notice: You will not see your weapon on your screen. If you want to undo the lower your weapon trick you can click the grenade button, melee, turn in monitor if your on forge, shoot, or just click all the buttons again.
Tip: This can be good for a machinima. But this can only work if this is offline.
So thats how to lower your weapon in Halo reach.