For a display replica, I’d probably start with period French ordnance manuals and museum collections rather than trying to scale it from photos. Those reducers seem to vary depending on the shell and fuze type, so a generic 27/28 cm dimension may not be reliable. Same problem with online offers, the headline number can look useful until you check the details. On a casino like
https://tropical-casino.com/ Tropical Casino, a bonus percentage or slot payout figure only makes sense with the terms around it. A straight-on museum photo with a ruler beside an original piece would still probably be enough for a wood or resin reproduction.