Here's something I pulled off the Internet a while back. Haven't tried it myself so I can't vouch for it.
"The Chinese 120-round AR15/M16 drum is very simple to use, same instructions to load and operate as the AK47 75 & 100-round drums. Excellent drum magazine, very reliable, as good as any other drum on the market. The 120-round AR15/M16 drum is also the highest capacity for the AR out there. It can be kept loaded forever, when you want to use it, just crank it up about 6 times and it's ready to go.
To load the drum:
Release the cover-clips to open the front cover.
There will be a spring-tension release button in the middle of the drum, pressit to release any spring tension, press hard if you have wound the crank. You will hear a loud snap of the spring releasing if there is any tension.
There will be a metal-follower that has to be in the very middle of the drum, this follower travels in a track so rotate it so that it is in the middle of the drum. When the drum is empty, it ends up in the feed-tube, so it must be returned to the middle of the drum before loading.
Once the follower is returned to the middle of the drum, which is the full-up position, open up your ammo boxes and fill it up with 120 rounds. Fill all of the spaces with your rounds. Once you have done this, turn the rotating follower to advance rounds into the feed-tube. If there are any empty spaces, fill and top off the drum.
Close the cover of the drum and crank the handle to put spring tension on the ammo to keep it from falling out. About 2 cranks will do. This is how you should store the loaded drum if you want one loaded. It can be stored indefinately, this way. When you need to use it, crank it up about 6 times and fire away."
Have fun and safe shooting.