I've previously performed shooting comparisons of several different coatings in a 6x45 and in a 357 rifle, and those comparisons led me to settle on oil-based polyurethane, but disappointing performance with the urethane coated plain base in a 6BR is forcing me to try a little harder.
So this time I'll be doing some different kinds of comparison tests, trying to understand what characteristics make a good coating, and trying to understand how coated bullets fail. The shoot-out will include oil-based polyurethane, an electrostatic applied polyester powder coat, an electrostatic applied silicone powder coat, and zombie green hi-tek coating.
Today was my first time ESC'ing bullets, so I'm sure I have a lot to learn about it, but here is how I went about it. First, I made fixture to hold the bullets base-up, because I'm going to be testing plain base bullets and I suspect that it is important that the base receive a good coat. I used a 1/4” center drill to drill an array of holes in an aluminum plate. The depth of the hole was chosen so that the coating would stop at the top lube groove, that way any “flash” would end up in the lube groove where it would do the least harm.
Using this base-up method, the base ends up getting a thicker coat than the rest of the bullet. That's not necessarily a bad thing, though, depending on your favorite theory of how coatings work. I believe coatings function similar to a gas check, protecting the base from melting and gas cutting, so I'm happy with the base receiving a thicker coating.
The silicone powder does not stick as well as polyester powder so my first batch of silicone powder coat turned out a little thin. About that time I noticed that the air pressure was dropping down to 5 psi while spraying, so I adjusted the regulator up to the recommended 8 psi and sprayed a second batch, deliberately putting it on a little thicker. This is that second batch.
If the shooting results are black and white, I may be able to wrap up this shoot-out in one day. But if the results are “muddled” then testing may drag on for a while. We'll see.
I'm also performing an oven test to determine at what temperature the coatings “fail.” I'm not sure if that's relevant to the shooting performance, but it might be.