Courtesy of David Noreen
Loaded Smokeless powder shotshells were first listed by Union Metallic Cartridge Co. in the 1891 catalog. The “standard” 12 gauge shells were in 2 5/8 or 2 3/4 inch lengths, but paper 12-gauge shells were however offered in 2 5/8, 2 3/4, 2 7/8, 3 and 3 1/4 inch lengths.

At the first Grand Smokeless Championship Handicap Live-bird Tournament given by the E.I. Du Pont De Nemours & Co. October, 1895 Capt. John L. Brewer used a Greener gun of high grade. His shells were the U.M.C. Trap, 3 1/4 inches long, 4 Drams of DuPont (Bulk) powder by measure; one trap wad, two pink felts, 1/4 inch 11-gauge wad and one ordinary 12-gauge pink edge wad over the powder and 1 1/4 ounces of No. 7 chilled shot.
The loads used are listed here, but not the shell lengths. Most competitors used 3 1/2 Dr. Eq. Bulk Smokeless. The longer shells did not hold more shot, but additional wadding.

The “Cast Iron Medal”, emblematic of the Live Bird Championship of America, was shot on Watson’s Shooting Grounds in 1897.
R.O. Heikes (using a Winchester 1897 pump) won the match by killing 91 out of 100 birds, taking the “Cast Iron Medal” and the $200 (about $6,500 today!).
Grimm killed 87 out of the 100 birds, using an L.C. Smith gun, 3 1/4 drams DuPont powder in a 3-inch U.M.C. Smokeless shell, for first barrel, and 3 1/2 drams DuPont powder in a 3 1/4-inch U.M.C. Trap shell in second barrel, 1 1/4 ounces No. 7 chilled shot in both barrels.

In 1898, Von Lengerke & Antoine, Chicago offered the “Gilbert Live Bird” load: 3 1/2 drams DuPont Bulk with 1 1/4 oz. No. 7 chilled shot in a 3 inch Leader shell, loaded by the Winchester Repeating Arms Co.

Wm. Cashmore Pigeon gun

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The 3" boomer era began with Western’s 3 inch ‘Record’ with 1 3/8 oz. of shot released in 1923; U.S. Cartridge Co. ‘Climax Heavies’ followed in 1927. Peters also introduced a 3 inch ‘High Velocity’ and eventually the ‘DeLuxe Target’ 3” with 1 3/8 oz. / 4 Dr. Eq. and 1 5/8 oz. / 4 1/4 Dr. Eq. to compete with the Winchester/Western 1 5/8 oz. 12 gauge 3” magnum introduced in 1935.