I have a rifle site barrel on my 390 20 ga. I would like to put a ff3 on it but haven't found one that fit. The gun is centered but shooting about 15" low. I have no more adjustment left in the sights. I can compensate but I have young shooters that will use this gun and I want to take out the guess work. I would put a saddle mount on it if anyone makes it, but I don't want to drill it.