I popped my adult kingsnake without any issue, the key is to not pop them all the way. Only enough to tell it is a male. That said, one thing males have that females don’t is a obvious “speed bump”. Start at the cloaca and gently press your finger down, then run it the length of the tail until you feel an obvious bump or a kinda drop off feeling. That will be where the hemipenes stop. It is hard to describe but if you feel it you will know.