When I go from 100 yards to 192 yds I require 16 - 18 minutes.
A few years ago, I used my Sierra Infinity program, and using Eley TEAM in the 1040 range, needed 40 minutes to go from 100 metres to 300 yards.
Shooting at a black mark on the bank, about 300 metres, another person spotting said I was close enough to go at 300 yds.
7 shots with one lot was just over 7 inches, and 5 shots with the other was just under 7".
This was a BSA Martini Int'l Mk II using target sights. That was the tail end of the ammo and the rifle has been sold too.