Bevel down will throw a better shower of spark to the center of the powder pan:Bevel up will get more frizzen surface but all locks have a mind of there own use tom fuller black English flints seem one flint will give me 65 shots or better.I also like missouri flints there are a good flint sell a little cheaper then tom fuller $8.00 a dozen great for target work and the flints last also I gotten 60 shots on one flint.I set up my flints not to hit square on the frizzen for range use I go with a little off-center only for hunting I have them hit square.