Contrary to an earlier statement, pinching caps into an elliptical shape is not inviting a multiple ignition.
The copper cap is pinched into an elliptical. It is then placed over a round nipple. The soft copper cap form itself around the round nipple, but the "springiness" of the elliptical shape is retained.
I have fired cap and ball revolvers since 1970, and often pinched the caps into an elliptical. This helps the cap cling to the nipple, helping to prevent its loss from falling off, or recoil.
Incidentally, I don't believe that multiple ignitions begin at the front of the cylinder, when flame somehow squirts past the ball. Haven't believed that in years.
I believe that caps fall off, or are loose enough on the nipple, and flame squirts into the nipple of other chambers.
Back in the 1970s, with the same revolver, I experienced multiple ignition on three separate occasions. This was with black powder, a .451 ball, Crisco smeared over the ball, and a cap not pinched placed over the nipple. Back then, I didn't know of this practice.
That revolver was irrepairably damaged on the third incident.
Later, when I obtained another cap and ball revolver, I learned of pinching the caps. I have never had a multiple ignition since, in a variety of revolvers.
The assertion that pinching caps invites multiple ignition is news to me. I've never heard that. Not in more than 40 years of shooting cap and ball revolvers.
