if they start to look thin, i'll step up the frequency for a little while b/c to me, that means growth spurt and they need more food. easiest way to check is just to see if the tail (the part past the cloaca, not the whole "red tail" part) is sufficiently full and rounded and not saggy or tapering too strongly. if it's healthy looking, then you're probably feeding at ok intervals. a lot of people will say, "i feed every 5-7 days and my snakes tail is perfect"... but a lot of those people haven't tried feeding less often and in my opinion, are probably feeding a little too often. just keep in mind when feeding, in the wild, these animals probably go for periods of time w/out eating that would blow your mind. want proof... ever seen a 5ft cbb bcc give birth? probably not unless it was fed conservatively. do you see wc bcc giving birth at 5 ft... yup! not often, but it happens! and that's b/c they're sexually mature (age), not "the right size"... whatever that is.
anyway... i've gone on waaaaaaay too long and i'll shut up now. those are just my observations, come up w/ your own 
jb
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Jonathan Brady
My Kingsnake Photo Gallery