The tumblers you are using are of better quality than the ones
I use (Harbor Freight) and have mine tumbling for weeks at a time.
So, I doubt that a more expensive tumbler would solve your problem.
I use the same, cheap, Harbor Freight tumbler, except I only use it
with stainless steel shot for burnishing sterling silver. I load it
about 3/4 full with approximately 1 teaspoon of burnishing soap, and
fill with water about 1/4" above the shot. Never had a problem
James in SoFl