with the flintlock 3" to 4" at 50 yds. is best I can manage.
This is good enough.
But, I have some questions to be thought about.
I also must say that I agree with,
Personally, I don't trust "minute of deer".
And also disagree with the pie plate/paper plate comparison that is often made (it does not include a margin of error).
Your 3 to 4 inch group at 50 yards is half of that vital area analogy. But, you need to stick to that 50 yards or less limit.
The questions I would ponder here.
Are those 3 to 4 inch, "best I can do," groups off the bench, standing free-hand, or from supported field positions such as kneeling or sitting?
If freestyle standing, how often do you get shots at deer where this position
must be used?
One rifle instructor you are all familiar with, or should be, said quite often, "if you can get closer, get closer, of you can get steadier, get steadier."
I doubt these 3 to 4 inch groups are the best the rifle can do. The type of lock mechanism should not effect accuracy intol shooter interaction with it becomes a factor. What is the best group off a bench? I get 3 to 4 inch groups with my smoothbores off the bench.
Can you get a more supported field position and shoot better?
Can you on a personal level, stick to that 50 yard limit and be selective in the shots you take? If so, I think you are good to go.