I just have remembered the Quick Loading weapon enhancement, which allows me to both have ass-slow mundane firearms for commoners and quickly reloaded magical firearms for adventurers within the same game. Thus there is much less need to make the firearms base damage scale with level/HD, as there is a cheap enhancement to get full-attacks going.
In the same breath, I have added heavily reduced reloading times for masterwork firearms (fluffed as breech-loaders) and masterwork ammo (fluffed as paper cartridges), which pushes the presumed techlevel of Ravenloft a bit but not too much as far as I am concerned. For dedicated gunners they will probably only matter for a few levels before Quick Loading gets affordable, anyway, and still be too expensive for the grimey Commoner conscript NPC armies.
Also, both Blunderbusses and Volley Guns now fill a cone, with the latter just filling a bigger cone.