I am assuming since it is being bore sighted you are using a fully rifled barrel possibly with a scope? If not don't bother with the saboted slugs, they will not work worth a flip. However from what I can gather you got a slug barrel with it.

I will say what the others did, you just need to try different loads to see what you and your gun like. It does get expensive, no doubt.

I have a buddy that has a 12 ga 11-87 and his likes the regular winchester saboted lead slugs in 3 inch. They are accurate and they work. I personally feel the better bullet designs like JCC mentioned would be better, but hey he kills deer with it so he is inclined not to change. And his slugs are a bit cheaper.

As far as not using 2 3/4 inch slugs in it. I don't know about that and I am pretty certain JCC will dissagree with that as well. Most of the 2 3/4 inch slugs work better and can have just as much power. You may find the faster slugs will not shoot well out of your barrel. From what I have seen most average slug guns like 1700 fps or under to shoot accurately out to 100 yards and beyond. You get up around 1900 fps and the accuracy seems to fall off at longer distances.

I will give you two more loads to look at as well. The federals with the barnes Expander bullets. Not the lighter faster ones (although you can give them a try if you want), but the one ounce slower versions. The barnes are a very proven bullet in the inline muzzle loading circle. Also look at the winchester Platinums, they shoot pretty well out of most guns too. I think the barnes would expand better though.

I have pretty much narrowed it down to these two bullets in my H&R ultra. I have not tried the core lokts or copper solids yet either though.

Paul