With my eyes aging rapidly, I’m considering this path as a compromise between mid-distance accuracy and taking the occasional duck or pheasant. I’ve got a 24 (.223/12) and a Valmet combination (.308/12) I’m considering this for. Not very classic, and I’m concerned about durability in the conditions of Montana—but iron sights are getting pretty tough.

A mate of mine put an Aimpoint Micro on a combo, and he loves it. Personally though I prefer a scope whose bottom end is about 1x to 1.5x. I have used several combos with such scopes, and they work well for birds, running game etc with the shotgun, while allowing you to take a good aim, even in poor light, with the rifle. I have shot trap with a combo equipped with a 1.5 - 6x, and shot any number of birds with that gun and with my drilling with its 1.5 - 6x.

The trick to it, if there is one, is to use the scope on its lowest magnification for the shotgun, mounting smoothly and looking straight through it to focus on the bird (ie ignoring the reticle). With a 1x or 1.5x magnification it is easy to do this, unless perhaps the scope was mounted such that you aren't looking through it when you mount the gun.

Dan oz is spot on. A low power scope can be mounted lower on the weapon so you dont have to build up the stock to have your eye aligned when the butt hits your shoulder.

combo gun


Drilling

I've recently acquired a 20 guage double, with rifled bores. I've shot it with the open sights and a Venom Vortex reflex or reddot or whatever it is called. I got to carry it the few times I was able to get in the woods in deer season. It carries nicely, nochange in balance or feel. It comes to my eye just like open sights, except I can see it more clearly. I can shoot better groups with it than I can with open sights. I suspect I would like it for birds, with the caveat that I am a poke and shoot, instinct shooter, not a place the bead, swing and follow through. I watch the bird and bring up the gun and shoot.
My drilling and BBF's all have scopes and I never pay much attention to them on birds, but they sure effect the handling.
Just my experience,
Bfly

I need pichers...

scope is the only way to go

I have a Blaser BBF97 12 ga over 308, and I have an Aimpoint H1 micro red dot, S&B 1-4 illuminated scope, and a Swarovski Z6i 1.7-10 all set up on QD mounts and sighted in. I choose the optic based on what the conditions might be.

I can also shoot it with open sights.

on the valmet, modify a set of low ruger rings, thats whats on the valmet in the pic above

I put a 2.5-8x36 Leupold on my Savage 24 .22 Mag./20 gauge and it made the shotgun barrel nearly useless for me on anything moving. A peep sight that nearly doubled the sighting radius over the stock barrel mounted open sight was a way better compromise for my rifle and eyesight.