I'm looking at making a whacky build which involves using a large double hackbut. Unfortunately, the rules in regards to the size increase come across as unclear.
For one thing, a small double hackbut is a 2d10 weapon, but increases to 2d12 for some reason, when usually a 2d10 weapon increases to 4d8. This is a bit confusing.
There is precedent for converting 1d12 to 2d6, however it is effectively a houserule or fiat to use this as it is a throwback to old school D&D where each 1d12 could just be converted to 2d6 and then adjusted. This would make a large double hackbut 6d6 (2d12 converts to 4d6, then size increases to 6d6).
Some opinions would be quite appreciated.