Claret Dabbler would that be suitable for hares and occasion foxes as well? and do you think a FLO would allow this?
So you want short as possible and it'll be used for muntjac so you need 1000 ft-lbs minimum. Check out the pistol section of the Hodgdon load data page and have a look at the rifle cartridges in there:
Set your sights on pistol reloading data | Hodgdon Reloading
223 out of a 15" barrel is struggling with that. Not saying it can't be done like but why fight to get it up there?
The 30-30 is easily small deer legal out of a 14" barrel.
So similar to this:
View attachment 64645
If I remember correctly Bewsher500 had a lovely wee Brno Fox in .222 for sale not that long ago.
I'm not sure if it sold or not, might be worth dropping him a PM

I'll still plump for a short combination gun for the OP maybe in .223 for the rifled barrel if he's unlikely to come across deer that would warrant the .243. I have a Blaser ES67 Bockbüchsflinte in 12b/.243 and it's a sweet little thing to go kicking around the hedgerows with. Here's one similar to mine but without the original Blaser scope QD mount:
Although I suggested the CZ 527 in .223, I have to agree with hybridfiat on a larger bullet, not too fast, if the woods are not open and the game is larger than a roe deer.
Make that a CZ 527 in 7.62x39mm.