The target's shape and colour, as .500 Nitro suggests, is vitally important to having a good sight picture & making good shots that give good information. A poor target will produce poor results that are not repeatable.

Also, 50 yards is a good range to shoot - I also suggest putting up 2 targets, side by side and shoot the left barrel at the left target, right barrel at the right target, or over on the right, under on the left. That was you'll be able to see exactly what is happening.

A 1" diameter white dot in the centre of a black square or disk makes for a good aiming point.

Also if you go to www.targetz.com - there are a lot of different targets that can be downloaded and printed off. Click on TARGETS, then down the page to target # 10142 as described below, is a good one for 50 yard shooting with a bead.

Concentric 1" wide black rings, 1" apart on a white background makes a good target for bead front sights as the bead is easily centred inside the next larger ring.

Measure the distance between your two barrel's centres so you'll be able to judge if the barrels are crossing or diverging their groups. Measure from the centre of a 3 to 5 shto group (each barrel) 1 or two shots is usually not enough to judge by. You should use at least 3 shots out of each barrel to get a good idea of how that load is shooting, accuracy wise as well as regulation wise.