I have never been able to find where x size patch works with any bore diameter. There are too many variables (exact bore diameter, patch thickness, jag or loop, diameter of the jag or loop, etc.). Since the late 70s when I started, it was always "grab a patch that looks proper based on the package size recommendations". From there, it may work perfectly, or not. Often, or most times, I get the closest working size and try it out, then it may work out. If it is too loose, try a bigger one, and if that is too tight, trim it a bit bigger than the loose one. Sorry that I can't answer your question and give you an exact size, but this is what you have to work with.What size patches are you using in your 30cal barrels (308 and 30br in my case)?
Im using a Dewey 30cal rod and jag if it makes any difference .
Also any of you make your own ? If so what material do you use?
Thanks