Lots of potential causes. Here is an easy solution,take a neoprene fishing glove cut the finger or fingers off, cut the fingers to about 3/4 " pcs or the size you require.Slip the cut piece over the area that you want to protect.Works great, inexpensive,and many pieces. If your trigger finger is getting hit by the back of the front trigger when you fire the second barrel,put a bandaid or two over the area, and wear shooting gloves. If you have both problems you may have to cut a small slit in the glove just above the neoprene area to allow the glove to fit.I'm very familiar with the problem, started shooting driven birds with a Charler Lancaster 1913 o/u, s/g, 16, small trigger guard, close triggers, and light weight! . takes a while for the knot on your finger to go down.
