Thank you all for your contribution.
My demand is: A deer rifle with a shotgun for buckshot, a small game rifle with a small game shotgun, a .22LR (cheap practising + legal demands while trapping in my state) and a shotgun/rifle combo for coyote hunting. I life in New England, so the typical distance for deer is less than 50 yards (I hunt them with a bow at a distance of 20 yards), small game less than 30 yards (so far hunting them with an airgun) and coyote less than 100 yards, maybe a little bit more.
As a humble person who is very much into experimenting with technical things and who thinks that one gun with one shot is all you need, I figured out this solution:
The 12/30-30 "as is" with a LeveRevolution or hand loaded should do the job for deer in the brush and in the open field.
The 12/30-30 with a sub caliber insert in .32 ACP and a 20ga (or .410) insert / .22WMR insert in the 12ga could be a small game combo or double rifle
The 12/30-30 with a sub caliber insert in .30 Carbine (<100 yards) or just it's 30-30 and a 20ga insert could be a coyote combo
The 12/30-30 with an insert barrel in .22 WMR and / or .22LR could be good for target practizing, the short .22WMR insert barrel plus an adapter to .22LR could cover the legal requirement while trapping
Another insert barrel in 375 or 444 could make a double rifle for black bear, moose and larger.
This would basically be a 24F with three holes in the stock, one for the 10" insert in .22WMR, one or the 12/20ga adapter and one for the 12/.410 adapter. The insert barrel in 375 or 444 would only be in the backpack on special occasions and a fine, long insert for .22LR would be the option for the trip to the indoor range.
A Krieghoff insert would be nice, but I didn't find a source or a price, not even on the German website. I found the MCA site but those guys seem to be too busy to answer silly questions about their stuff.
I am also willing to try different adapters or to make chamber adapters myself (not a complete insert barrel, I don't have access to machinery of that kind). See my future combo as a tool for making distant holes in combination with an ongoing project.
My idea of accuracy: The vital area of a deer or a coyote in less than 200 yards in the field with the 30-30, the head of a squirrel in 50 yards with an adapter / insert barrel and somewhat in the MOA range with a decent insert barrel in .22LR or .22 WMR on the range for having fun up to 200 yards.
Does anyone know if the 24F will be available with the Accutrigger? I dry fired several 24F at my local gun dealer and the trigger did not impress me (compared to an Accutrigger or a Thompson Center).
I have to admit that I grew up in a part of this world where you don't have the right to own a gun, so far my only firearm is a T/C muzzleloader. Does this all make sense or is this all a pipe dream of someone who has no idea?
Thank you for any input.