In 1900, the year you say your gun was rebarreled to 28-gauge, I only find the few 28-gauge shells North American ammunition companies were offering to be 2 1/2 inch with a load of 1 3/4 drams of either bulk smokeless powder or black powder pushing 5/8 ounce of shot. By 1901, I find that in addition to the above, UMC was also offering 28-gauge NPEs in 2 7/8 inch length. A few years later the loaded cartridge listing offered the 2 7/8 inch hull with 2 drams of powder, but still only the 5/8 ounce of shot. The high velocity 28-gauge loading using progressive burning powder in a 2 7/8 inch hull pushing 3/4 ounce of shot came out in 1932. Shortly before WW-II the ammunition companies began phasing in the 2 3/4 inch 28-gauge shell and pretty quickly after the War the 2 1/2 inch and 2 7/8 inch 28-gauge shells were gone from their offerings.
RST offers a delightful little 2 1/2 inch 1 3/4 dram equiv. 5/8 ounce of shot 28-gauge shell, delivered to your door in most states.
http://www.rstshells.com/rst_classic...shotshells.htm
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