BPs in particular can be hard to pop as they get older. If you have an experienced keeper or herp vet- probing is the best way to id the sex of your snakes.

I pop babies & if I see hemis- they are boys; when they get older & probe the "girls" just to be sure. VPI has a great vid on how to do both methods, but I practiced with my Herp vet & other keepers to get comfortable with both methods. It takes time & I am still more comfortable probing than popping.