I've hunted deer a long time with fair success. I've got a .40 flint too, though fairly new. I do plan to take a deer with it, under circumstances I can forsee to some degree.
An odd shaped bottom where a wet branch feeds a 50 foot wide creek. The longest shot is 50 yards and 5 yards wide, the next longest is 29 yards, some are 7 yards. I get one or more there every year and have for years. Lucky to be in NC, where the state now gives you all the tags you want on request in the eastern zone. Got one 4 pt. this last season at 17 yards with a cartridge gun, the first time I've ever seen a bullet impact before the recoil drove the scope off.
I am just thankful to my maker I can still hunt and make a short drag to the path I can get the truck to. Those young guys with magnum itis razz me endlessly when I seek help. You know how it is. I have to do something to keep them in awe. Heck, many of them miss, few can track, and some are even skeered in the woods at night.
Use your 40s. Set up the hunt in your favor. If you don't feel its a good shot, just wait. That's no different than watching a great deer that is too far, no matter the gun.
I once carried an 8 X 56 M-S ten years, a few days each year, without a shot until a perfect Ga. woods deer, 10 point typical @ 16" fell to it. Thats my life time eastern whitetail trophy, even though I have larger mounted. A poll isn't required to hunt as our forefathers did. The spark is in you. Lon