I’ve never shot Pyrodex with 209s, but since it works with caps, I suspect any 209, except maybe the special 777 ones, will be fine. Those might even work, but are a bit weaker to reduce buildup with 777 and its kin.
Never had an issue with blowback or sticking primers in a break-action, but I suppose it might happen. With the primer supply being what it is, I doubt you can pick and choose. Keep that flash channel clean regardless.
