SHB p.39
Drilling a "dimple" in the barrel would NOT be considered an outlawed external modification as it would not be visible when the revolver is fully assembled and ready to use:
SHB p.33
Up until the December 2015 TG Summit, it was a MSV for retrieving dropped rounds:
2) Should the MSV for retrieval of dropped/ejected ammo be deleted?
PASSED - For 88.56% Against 11.07% Abstain .37%
Regarding dropped/ejected rounds...suggest reading the Ammunition Conventions section on p.28 of the SHB.
The shooter may retrieve them if done safely.