I want to paint some dummy rounds to use for practice for my 38. I tried model paint but it goes on thick and rubs off very easily. Any ideas?

Drill a hole in the side of the casings.

Blue the cases.

I use a red sharpie marker

__________________
Regards,
Guy-Harold Smith II

Easy. It doesn't rub off?

I tried to do that but the case kept moving and if I put it in a vice I think I might bend the cartridge.

I just paint the back of the cartridge Black. It lasts pretty much for ever unless you use them every day. Mine are still in excellent shape after 10 years or so. Revolvers do not mark up the rear of dummy cartridges except where the primer gets hit.

Drill a big hole through the primer pocket and spray paint the bottoms with fluorescent safety colors. There's not much friction against the head of a revolver casing.
Edit: CHief38 had the same suggestion, only faster.

I'm sure it will eventuality rub off a bit on the high spots, but it stays in enough of the recesses around the rim, the lettering of the head stamp and the step from the case to the bullet to be pretty obvious. I have yet to need to mark them a second time, but do keep plenty of markers on the bench in case the need ever arises to touch them up.

__________________
Regards,
Guy-Harold Smith II

A wooden dowel would make a better holder and prevent crushing

This seems to be easy to over-think. My "dummy" rds are just empty cases with a bullet seated and crimped, no primer. Easy to see there's no primer with rds in a revolver cylinder. If I wanted more (speedloaders loaded with dummies where you can't see there's no primer?) I'd color the bullet with a sharpie.

I use empty cases without primers. The practice rounds never get anywhere near live ammunition, so a mix-up is unlikely. Still, I always double check to be certain none have primers when I use them.

I punch out the primers and replace it with a piece of colored rubber or soft plastic and a drop of super glue to keep it there. Then drill a hole or two into the side of the brass casing.

A drill press and a center drill bit will help.

CARBIDE CENTER DRILL | Brownells

Blue Dykem machinist's marking spray is what I use.

__________________
-jwk-
US Army '72-'95

Black Magic Marker doesn't rub off very fast, especially from the head. Just mark a few stripes around each case.

A black paint marker or a good old Sharpie will last a long time. Use the Red Ink from the IRS - that will be around forever!