Panzerace,
I you want them to be clean, fast, simple and consistent, just use decal film. Most Hobby shops should have it in stock, and if not defintley easy enough to find on line. 1 sheet should be enough to do just about every tank you own or will own that you want to add kill rings too. Solid decal sheet ususally only runs a couple bucks a sheet, and is available in any color you would most likely use (white, yellow, red, or black).

Simple cut to width with a sharp x-acto and a straignt edge then cut to length and then wrap around the barrel, all you have to concern yourself with is consistent spacing, piece of cake!

Just my 2 cents!

Streetsquid