Small game is killed by damage to vital organs and body structures brought about by subsonic pellets. The idea of hydrostatic shock being involved as in a supersonic rifle bullet is false.
Any mushroomed pellets won't aid the killing effect; if they were deformed prior to striking the target then they will be travelling at reduced velocity and thus have less lethality, and if they deformed when striking bone within the animal, then their job has been done.
About three lifetimes ago I did a fair bit of work on nickel coating of lead shot with IMI Kynoch in Witton.
copper and nickle plated shot is even harder than high antimony shot.
Actually, they aren't. The coating is so thin that any crushing test will detect hardly any difference. The coatings work by resisting and preventing the lead pellets cold welding together under the pressure of their initial acceleration, and thus not allowing the pattern to degrade.
There is a suggestion that they penetrate better than plain lead, but I never got involved in measuring that side of things. A bit of anecdotal evidence for you however ...
When I was shooting wood pigeon big time I found that an Eley nickel plated trap No 7 (Brit) was about the best cartridge I could use, very markedly so for those birds that dropped into nearby trees or settled on the ground in the decoy pattern. With the birds wings folded an ordinary shell wasn't always very reliable, but the trap job seemed much superior.
Others may have seen something similar?
Eug
