This is my second try at putting a red dot on my 1377. I have the steel breach installed. First I tried two different cheap reflex sights that were defective. Ordered a Bushnell TRS-25 and mounted it on a dovetail to picatinny adapter. Tried to sight it in today. It’s shooting 4” low. Good groups at 10 yrds but can’t get it to elevate aim point. Maxed out elevation with no change... Is shimming my only option?