Some years back I had a really odd experience with spreaders through open chokes. I had just purchased a 16 gauge Uggie and a case of spreaders. Since this gun was going to be used on blue grouse at 10000 feet, and I was expecting something on the tight side of improved cylinder and modified for the Uggie, I thought the spreaders might help a bit with high altitude pattern spread. I went to the skeet range and proceeded to shoot the worst round of skeet in my life. Of the few clays I hit, many really disintegrated, and sometimes we heard an odd whistling sound after the shot. A trip to the pattern board showed that the majority of spreaders out of the improved cylinder barrel (later measured closer to skeet) where not opening at all. The pattern board at 25 yards showed something akin to a fuzzy slug: a very sharply defined center hole with a sprinkling of shot around the edges for an inch or two. A call to the manufacturer revealed that they had just started a new wad in that load. The consensus after some tests was that the spreader insert was acting as a cap to the shot and the open choke wasn't disrupting the shot column enough to get things working the right way.
