Weight limits were being established by the mid-1890s, which likely put the end to 10g guns in competition. Shot was limited to 1 1/4 oz. for both 10g and 12g so no advantage to 10g

At the First DuPont Grand Smokeless Championship Handicap Live-bird Tournament October 1895 all guns were 8 pounds or less, and the usual load was 1 1/4 oz. shot with 3 1/2 Dr.Eq. Bulk Smokeless powder. Gauge was not listed but it is assumed all were 12g.
https://digital.la84.org/digital/collection/p17103coll17/id/53099/rec/2

The 1898 GAH at Live Birds limited guns to 8# 'naked' ie the barrel guard and 'recoil boot' were not counted

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