RTI RPB .25 barrel and slug sizing

Hey guys . . . I just picked up one of the subjected from the rtishop in Spain. It will likely be here before the end of the week. Question for any of you who may have one - .249, .250. .253, etc . . . . what size slug have you found to work best with yours? Obviously mine be be different but . . . . here's hoping for some consistency in their mfg process and 8 out of 10 are <XX> sized . . . ? That'd be spiffy. :) Stephen ( I think that's his name - the guy from AVS slugs ) is able to produce .25 cal ammo in various sizes - hoping I can get a ballpark / rough idea as to what this barrel might be from those of you who have one.

Thanks . . .