For an underbarrel tube- place gun on safe, tilt muzzle up at a 45 degree angle, and turn gun so that trigger is up. Twist the end of the magazine tube to unlock it, pull tube out until the loading port is open. Drop cartridges in the opening one at a time, bullet towads the muzzle. When you have loaded the number of rounds the rifle holds, slide tube back down, twist to lock in place. Turn rifle back over, operate bolt to chamber a cartridge.
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