HI,
Have been working on a wet tumbler. Making it from a treadmill. Have a 15 & a 9 inch piece of 8 inch pvc schedule 80 pipe to use for drums. My questions are. How many pounds of pins should I use in each drum? What size pins do you recommend? What RPMS should I turn 8 inch drums? Should be easy to change as it is dc motor and will be wired to be variable. Been playing with it with a 12 volt lithium drill battery and am getting 34 RPMS with it. Also have several feet of 6 inch schedule 40 pvc. If I decide to make smaller drums, what RPM should 6 inch drums turn?

Thanks in advance
Doug

When you make the "drums" there must be "ribs" or some other device on the inside walls of the drum to mix up the tumbling media and brass. Smooth walls will just have the mix slide inside and the quality of the polish will be poor. (been there done that)
I use a 1/3 mix of tumbling media to brass and a squirt of Dawn dish detergent.
By the size the will fit through the neck of you caliber cases. You will get stuck media in primer pockets and some times in a case as well.
A coat hanger wire works well in dislodging the stuck media.So does a inertia bullet puller.
Lee decapping die clears the primer pocket instantly.
Most of the tumbling media is not high nickel stainless-steel and it will rust.
Since the media is expensive you can also use steel .177 BB's. They will rust but last a long time.
Make sure you have a strong magnet on hand. You will dump media at some point and the magnet makes clean up a breeze.
I dry and separate the media from the brass on a surplus autoclave screen pan. It cuts down on the drying time and rust.
My drums are running about 50 RPM.

I have a Thumler's I bought in 1976, and I use a pint of steel BB's, a cup of water, and one drop of dish soap.
I'm not sure what the RPM is, but it's not fast, and as RapidRob said, you need a rib or something inside (like you see in a clothes dryer) to agitate the contents gently as it turns to achieve the desired effect. (the inside of a Thumler's drum is not round)