I had to leave one of ours uncastrated last year as I just wasnt happy I had got it right with the bands, he was born with big horns and big everything but somehow the balls didnt seem to work with the band.
He went off yesterday with 4 castrated boys to the abbatoir, its not the best time of year to send them but I got fed up of him trashing the fences and charging me! (they are shetlands so normally left another few months before they go off). So recommend sending them maybe Oct time of the year they are born rather than waiting as I did if you have any entire, have learned my lesson!
I went on a lambing course at local agric college so could practice castration with the rings, would recommend it, we practiced on dead casualty lambs. Also got vet to do the first couple and watch me doing it. Still nerve wracking but I can do it myself now with reasonable confidence.