Hi CMOS,
If you can, find a 4'x4' piece of 1/2" ply, mark a black dot in the center, retreat about 25yds, aim at the dot and shoot it (with #8 or #9 bird shot).
With your cylinder barrel, you may cover most or even all of the wood with your shot pattern. Inspect the pattern carefully. There will be some clear patches with few or no shot (holes, suprisingly big too, eh!) and towards the outside edges of the pattern there will be stray shot.
Lengthening the forcing cone is supposed to clean this up and to regularize the pattern. When the crimp at the end of a cartridge opens in the chamber, the shot then travels through the forcing cone, where it gets somewhat compressed as it enters the barrel. By lengthening the forcing cone, you are slowing the compression of the shot. This reduces deformity in the individual pellets and to some extent smooths out the progress of the shot and the wad (which is pushing the shot) down the barrel. As a result of this and less deformities, the shot flies truer, therefore the pattern is better. It is not tighter, but it should not have as many holes in it or as many stray shot.
If you need a tighter pattern, you have to get chokes, its as simple as that.
To throw a little spanner into the works, most modern, plastic shotgun wads rotate somewhat in a smooth barrel (not nearly like rifling, though). Shot emerges from the barrel spinning. Further the individual pellets travel down range at slightly different velocities creating whats called a shot string or trailing shot. Therefore, when a shot fired at a piece of plywood 25 - 30 yds. downrange meets up with the stationary, solid, vertical plane, the pellets will strike it over a period of time. So, is the pattern left on the board, representative of the quality of pattern thrown by your gun with a specific cartridge.
Talking about fishing, these lures are getting very expensive and won't make a bit of difference to the guy casting flies, for bass, in a sport fisherman, off the coast of Florida.
Blue Bunny, keep on posting. I like it.
ENJOY SHOTGUNNING and try ISSF Skeet.