WHICH BARREL SHOULD YOU SET UP WITH A CHOKE YOU WANT TO SHOOT FIRST IN AN OVER AND UNDER, THE TOP OR BOTTOM, AND WHY?

Set whatever barrel you want to shoot first if you have choke tubes, just use the more open chokes for the first shot and tighter ones for the follow up. If you have fixed chokes you will want the more open choke first as that shot is typically the closer one and the tighter pattern will hold longer for the second shot. The barrels are regulated to have the patterns meet at 40 yards on most guns. You will typically find the top barrel to have a tighter choke on fixed guns also. By far the best thing you can do is get out and pattern the gun, shoot at a 30 inch circle at 40 yards and see what it does and where each barrel shoots. You will gain more info from that than anything else.

You want to shoot the under barrel first. This is because it is lower and more in line with the stock, therefore the recoil will be directed straight back with less muzzle jump. Less muzzle jump will theoretically allow you to get back on the target faster for a second shot with the top barrel if needed.

Thank-you, I've been shooting this way, the bottom barrel first, top second, with the more open choke on bottom, I just never knew if that was correct and why. I appreciate the response!

My O/U shoots bottom barrel first. I never thought about switching it, but maybe cause it shoots just the way I like.

I have sxs guns now but when I had O/U's I shot the bottom barrel first, generally. It seemed to have less muzzle jump.