Thats interesting maybe they were gunnery trainers.
When I* trained on Chieftain Mk5 and the CVR[T] series in the 70's we used dummy turrets, with a .22 calibre rifle mounted, against rubber scale tanks, some that moved by a piano wire and motor, on an indoor 25 meter range, to practice the duties used in the turret and those techniques that were part of a gunners job. This is of course prior to laser sights, when gunners had to estimate fall of shot and such things when firing. It was of course cheaper too.
Thanks for sharing such interesting and unusual pictures.
Regards,
John