Here's my barrels, the original and a home made, i find i use the homemade more often, i used to use river gravel but now i use ballbearing, works much better and faster especially when used with barreling soap B.
Barrels without the fins in are for stone polishing as the stones need to slide
Metal barrels all have fins inside usually 3 to tumble.
in the homemade one i used some offcuts from plastic corner protectors and epoxy to stick them in.
The machine is a bit yukky as the bought barrel sometimes leaks,and also you need to oil the spindles, i got it of fleabay for 20€
the rubber bands are made from old car tire innertube to help grip and lift the barrel clear of the rollers