Daryl
Not very deep 0.010 " max.
The hard lead 0.735" balls did not over tighten the tubes.
Even the full bore hard lead slugs 0.750" long with 3 x 0.110" bands (0.330") bearing surface did not cause choke removal issues.
Nitro.

Edit: I quoted 20 ga ball size not 12 ga, corrected.