To chamber a round, lock the bolt back on an empty gun, lock CH in receiver, insert loaded mag, and hit bolt release. Do not use the CH except to lock the bolt back. Safety should be on.
Second method, most widely used and recommended. Insert loaded mag in unloaded weapon, pull back ch and let it fly. Safety should be on.
In all cases keep your finger away from the trigger. Do not touch the trigger. Keep your dirtys digits off the trigger. Do I make myself clear?
Riding the CH down is sure to cause a jam.
Before anyone raises objections (which you could with the way I type sometimes), this is the method by which the gun reloads itself when firing. The bolt must move forward with enough energy to strip the cartridge from the mag and move it into the chamber and lock the bolt. The first round out of a fully loaded mag has the most pressure on it and is hardest to move so let the recoil spring do it duty.