As far as pressures. The old paper shells were much thicker than plastics. Definitely raised pressures in them. The other thing was they seeeed to increase gun recoil...noticed more so in break open shotguns which seemed to have more drop in the stock. Increased pressures more so with 3 inch in 2 3/4 inch chambers. Back when I worked on guns I did the conversions on Browning 16 ga making the ejection port longer. Also extended the chamber and forcing cone. They did seem to shoot better patterns by doing so. Not a hard job but it was more time consuming on the Browning. I also remember fitting a few 3 inch M-12 bbls to 2 3/4 inch guns but it was a bit more extensive. Not many know the original length of 410s was 2 inch and originally the 28 was marked as 2 7/8 inches. The plastic wads sealed the bore better than the old card wads so they could use somewhat smoother bores. Powder charges were reduced with plastic wads too
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