What interested me, so I did a bit of reading, was that my BCG injection was with a "jet injector". It turns out that, even in the mid-1970s when I had it, these weren't new technology, and I found a 1970 paper discussing their use (
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2427792/pdf/bullwho00209-0064.pdf).
The conclusion of this particular report is that the calibration of the dose is less accurate than vaccination by syringe and that "the risk of unpleasant reactions is ... increased".
So I guess I was lucky in that I found the injection completely painless and had no after-effects.