I think that a Jeager rifle is a great choice.
Back when I thought that the caplock rifle was the only sensible b.p. rifle, I decided that if I was going to have something as useless as a flint, it would be because I put it together. With a nod toward my Germanic heritige(1/4), I picked a jeager.
I haven't bothered picking up a caplock since I started hunting with it.
THAT is the bad boy of hunting rifles.
A 15-18mm rifle would be perfect for practically any forest game on four feet, most certainly boar and stag. The one I built is 58, but if I did it again I may go 20ga or larger after the reports of others on the board.
There are techniques that will make that rifle more dependible than not.

I have never really had a problem with flints in general(could just be luck), but the angle that it is knapped and the heat treatment of the frizzen are very important to a good spark. I use a piece of sheet lead to hold the flint into the hammer.
Keeping the flash hole clear and the priming powder to the outside of the pan make a huge difference as well.

Once again, I am sure that others can fill in details and gaps to the techniques especially when the weather doesn't cooperate.

Cheers

Tom