This rationale makes a lot of sense, particularly with a more square load. I could see a loss of SOME pattern density in the center, but not really a hole. To that end, someone on the SSM Board posted the following which I thought was interesting . . .
This question comes up from time to time, so I wanted to share some pattern results from three different spreader loads. The three shells I patterned were RST Spreaders (1 oz of 8s), Polywad Spred-Rs (1 1/8 oz 8s), and Fiocchi Interceptors (1 oz 8s). The RSTs and Polywads met the nominal pellet counts of 410 and 461 respectively, but the Fiocchis had 423 pellets.
I shot these patterns to see if using these loads would allow my "pheasant" gun to work for grouse and woodcock. I used a Verney-Carron 12 ga. sxs with 28" barrels stamped 18.4mm and choked R 0.008 and L 0.023. For an indirect comparison, this gun shot 70% and 65% patterns at 25 and 35 yards using Federal Top Gun loads (1 oz. of 8s).
I shot five patterns for each load at 15 and 25 yards (reflecting typical grouse and woodcock shots).
15 yards:
RST - 92% (range 90-93%)
Fiocchi - 86% (range 84-88%)
Polywad - 77% (range 69-81%)
25 yards:
RST - 71% (range 57-80%)
Fiocchi - 64% (58-74%)
Polywad - 41% (range 36-55%)
So, based on these patterns, the Polywads open faster, but lose pattern efficiency quickly. The Fiocchis offered some improvement for the IC choke in the right barrel, but the RSTs did not fare as well in that regard. Both the RSTs and Fiocchis had less variability in their patterns than the Polywads.
I used HunterJohn pattern sheets that have a life-sized duck outline in the center, and counted pellet strikes on the duck to measure density at the center of the pattern (maybe not statistically accurate but seems to make field sense). I came up with the following percentages of pellet strikes:
15 yards:
RST - 27% (range 24-31%)
Fiocchi - 24% (range 20-33)
Polywad - 10% (range 5-20%)
25 yards:
RST - 13% (range 10-14%)
Fiocchi - 12% (range 11-14%)
Polywad - 5% (range 4-8%)
Based on these patterns, the RSTs and Fiocchis had significantly more pellet strikes on the pattern "center" compared to the Polywads.
My take-away was that, at least out of this gun, the Polywads will provide a more open pattern, but the trade-off is less density in the center and a pattern that will not be effective much past 20 yards, even out of a tight Mod. choke. Overall, the Fiocchis offered the best performance for opening the IC choke while maintaining good performance at 25 yards out of the second barrel - both in terms of overall pattern efficiency and pellet strikes at the center. YMMV of course depending on the gun and load used.
