Height of express sites for s/s

[Mizar]

Hello. I plan to make an express rear site for an old s/s 16 gauge shotgun with sawn off 20" barrel. The distance between sites will be around 15".
So, please, can you provide me with some approximate measurements about the difference between front and rear site heights - the shotgun will be sighted in to POI at 35-40 yards with Rottweil Brenneke slugs. And if someone knows what must be the angle between the sites line and the bore axis it will be great.

Thank you in advance,
Boris

 

[35Rem]

no way to know. Each barrel will probably shoot to a different point, anyway. Shotgun barrels aren't regulated like double rifle barrels.
This is even worse for sawn off shotgun barrels.

It will be a trial and error proposition. I'd start with some cheap slugs, maybe even bird shot a little closer to get an idea of regulation and sight height.

 

[Mizar]

You are right 35Rem. Also, the angle between the rib and the barrel axis is the most important. I started to think about this AFTER I posted... Well, it will be fun to find the POI.

Boris