Do you have a reptile/pet store near where you could buy a small and a medium and take them home to compare to your animal? If in doubt better to err on the side of too small than too large with BC.
If smalls are really that much thinner than your boa you could feed two every two weeks or so in the event that you get a bag and they seem undersized. I did the same when I was moving my Suriname from hoppers to small mice. Gave him two hoppers every 10 days until I ran out and then moved to smalls at the same interval.
I know what you mean about seeing a bump because you know there’s a rat in there hah! Small mice I’m pretty sure don’t leave a bump in either of my boas anymore, but I still feel like I see it. Luckily the lower end of my bag of large mice is only slightly larger than what I’ve been feeding for a while. Will make it easier to stair step their way up to larger prey.
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