I use the slapshot for the wild boar, I don't risk getting close to them when injecting! never had a lost or broken needle. The domestic pigs are in radials so they can be enticed into the hurdle pen for vaccinating etc, I usually bucket feed them on the fence line and vaccinate them in the open, but I have been working with them for a few years so have developed the rapport with my stock.
Another option to restrain pigs for injecting, tagging etc, is to use a rope noose through the mouth and upper jaw,as the pig pulls back, you hold them steady and you can do any quick operation such as injecting, tagging or ringing.