The flints I use for all my rifles are 5/8 wide by 3/4 long. Most of them are Thomas Fuller Black English Flints, although I do have a couple Amber French flints in there also.
If you go to the 3/4 wide flints they will work fine. But sometimes in rifles they will over extend the width of the frizzen and jaw. And then you will see corners sticking too far out from the side of the frizzen. Sometimes when you shoot the wider flints they will shatter corners off. Which can ruin the flint. I use the 5/8 in my Lyman Great Plains Hunter and my two Lyman Trade Rifles and they work fine. But maybe they are made to use a 3/4. Although I just checked my Trade Rifle and that 5/8 does look the same width as the frizzen.
I have a pan flask primer that throws 3 grains. It works pretty good but the more you use it the more temperamental it can get. If you find that the little pan flask wants to stay open... take the nose off. Inside you will see a spring that basically closes the lip on it. In that, you push down in the nose, that opens the lid, releases powder and as you let up on the nose it shuts the lid. If you see that the thing is still throwing powder after being released, take some alcohol and a Q tips and clean that area. Make sure it is dry before putting it back on the tube. Then the door will open and close easier again and it works fine then.
When the flint is in the jaw, and the frizzen is on half c0ck.. there is about a 1/16-1/8 open area between them. Remember, that flint has to push on that frizzen in a downward motion to make the spark and to make that frizzen spring grab and pull it out of the way.
there have I confused you good... I know I am.