- Since he stated the bullets were fitted with bastic heads, bastic may be a material of some kind.
Cuttin' Edge, a Dalek Bounty Hunter of the Wayfarer during the Second Dalek War, used bastic-headed ammunition to infect a Dalek with a virus that gradually ate away at its (Time War) casing. However, the Dalek was able to trasmit defence protocols to other Daleks, so the bullets no longer caused them damage afterwards. (PROSE: Prisoner of the Daleks)
Eventually, Dalek force field technology advanced to the point where bastic bullets were no longer effective against them. This was the case in the Battle of the Game Station in 200,100, although at least one Dalek was blinded after being shot in the eyestalk. (TV: The Parting of the Ways)