Re: bought used lyman deerstalker; issues flint,sling
I use hand-knapped flints in my buddy's deerstalker. Not sure where those particular flints came from since my dad gave them to me, but I believe they are English knapped flints. Great spark, I am on 20+ shots with the one that is in there. I also have great success with this rifle and really like it. I whacked a groundhog with it this summer, ~90 yards off-hand with a PRB over... 85 grains of 3f? IIRC. It's a great gun, congrats on your purchase and esp. on your first flintlock deer. It's a great accomplishment! As far as your sling problem... I have yet to be able to solve the same problem myself. I never ended up putting a sling on it because of the lug being too tight to take the swivel. Not sure how it's set up never having looked at it, but could you grab the swivel with pliers maybe and unscrew the lug from the ramrod guide, then screw it all back together? I'll take a look at my rifle.
Edit: You should be able to do what I suggested above from looking at the rifle. Just loosen the entire lug and tighten the screw to the barrel, and then screw the lug back in. I'd give it a shot?
A bad day hunting rabbits beats a good day of anything else!