it could be underfeeding.

intuitively, its hard to see how much heavier rats are. a hopper mouse is at 7-15 grams, a weaned rat is at 30-45 grams. that 3 to 1.

adult/jumbo mice and rats diverge even more. extra large mouse: 25-45 grams, extra large rat: 275-375 grams. thats close to 10 to 1. when a very large BP is hooked on mice, a feeding can really be 7 mice in a row.

for a young BP, rule of thumb is that the food they get every 7 days should be around 10-15% of body weight. so your BP is well in the range of weaned rats, and would need 3 or 4 hopper mouse or one really big extra large mouse.

also i would suggest you switch to grams completely. ounces are becoming more and more obsolete. feet and gallons are still going strong, but ounces are really unusual by now.

here is what i found and use as reference for the weights:

http://www.rodentpro.com/catalog.asp...el=frozen_rats
http://www.rodentpro.com/catalog.asp...el=frozen_mice


but i dont know about the weight loss of your corn snake, that seems really unusual, there may be an underlying issue here. maybe something like an infection or internal parasites. maybe its just a fluctuation, but the numbers look almost too dramatic for just a random fluctuation.