I have acquired a Parker Bros. "Trojan" 16. Really nice gun. They had a different standard for "entry level" in 1924. But I can't get a measurement on the chamber length. Visually I can see the transition, but I can't "catch" the corner of my scale to determine if the chamber is 65 or 70mm. I have plenty of RST 2 1/2" shells, so that's my default. But does anyone know when, if ever, Parker switched to a 2 3/4" chamber?