No, he just shot it until a ring formed. Might have taken 5 shots or 30. Then he reset the barrel and rechambered it and tried a different test. Some of Bell's tests did show a higher pressure at the bullet's base than, what was it, an inch below that. It's not an abnormally high pressure load that does the ringing but the result of the directed pressure wall hitting the bullets base and exerting its concentrated force sideways. It's like a shaped charge effect - https://en.wikipedia.org/wiki/Shaped_charge