Sorry to be negative here but.....
The propane delivery folks tell me don't even think about cutting that bottle! They claim propane is in the pores of the metal and cannot be made safe enough to cut. It takes very specialized equipment to do this safely.
Having said that, there are ways to cut the propane bottle by filling them with water and cutting just above the water line. That's still a big gamble. They do go BOOM.
Sometimes you can find freon bottles that are about the same size as propane bottles. They are much safer to cut without concern of creating an explosion.
Hope this helps.