A quick look at a number of SXS's muzzles shows the top of the rib in relation to the top of the barrels varies greatly. A LC Smith that I own has its rib much higher than the top of the barrels and a French gun that I own has its's rib below the top of it's barrels. I don't think that you can judge where the pattern center will hit by looking at the gun. You must pattern it to see. It all basicly boils down to stock fit assuming that you always hold your cheak to the stock. Case in point. I purchased a 28Ga with it's stock a full inch longer than I normally shoot wich is 14 1/4". The gun with it's long stock showed some barrel when mounted and I was able to hit with it regardless of the overly long stock for me. I removed 1" to make it 14 1/4" and now it showed what seemed to me to be an excessive amount of barrel. I thought that wow this gun is going to shoot high and was going to start to rasp the stock comb down so that I would only see a "normal" amont of rib. I took it to the pattern sheet with a rasp ready to start grinding away and wouldn't you know that that gun centers it's pattern 50/50 to the bead! Thank God I patterned it before I started rasping away wood or I would have to restock. It shows alot of barrel when mounted but hits dead on. I was actually hopeing that I could make it shoot slightly high but it shoots well like it is. I think stacking beads and what is the proper amount of rib showing is a bunch of molarky. Where the gun shoots for you is what counts. A center pattern or one that's a little high is best. I even shot trap with a field dimension stock as I don't want to spoil myself using a trap stock. That's fine if that's all you shoot but when you do it all it pays to keep the pattern center near the bead and adjust your swing for the diffrent shots that occur.