My Burm is a similar size to yours and some say she's small but growing slow and steady is better imo.
I've seen some videos of people ramming chicken bits and ribs down a Burms throat following a rat just to get the poor snake to grow fast which is crazy.
Admittedly I've been obsessing a bit myself but I think he'll be fine with a bigger size as long as it's only one prey item no more than once a week. I read somewhere they can eat something 5 times bigger than their head.
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