I just flew from UK to US and back, going through about 3 security checks each way. They did a random frisk in the UK. The only time I got anything swabed was a random check of my laptop in Minneapolis. I had no problems at all. I was wearing the jacket I shoot in, and I've shot .22, .223, gallery rifle and black powder.
I suppose if that didn't set off their sniffers freshly washed hands after a reloading session wouldn't set off alarms. I don't know just how sensitive those swabs are. Someone else can run with that one.