If the leather is thin enough to wrap around the ball, then use it. But take your micrometer, or caliper with you when you go to that junk yard. No sense spending lots of time, much less money, getting some fabric that is too thick to fit your gun.
For Wads, you would usually want thicker leather than what is used on car seats, and other upholstery. That is where belts, skirting leather, harness leather, etc. serve you better, than something much thinner.
Now, If you cut the thin leather fabric larger, similar to using .58 cal. wood wads in a .54 cal. rifle, then you might be able to use that leather for wads, too. I have never tried that. I have used wool felt wads, but not the oversized variety yet, that RB suggested in a post some time ago.
You raise a good suggestion to explore. :thumbsup: