I actually used one of the Bren / 25 Pounder combinations back in the late 1950's. It was in the basement of the Armouries and we mounted it. Then we took it to a local Gun Club range, and made a wheeled dolly with a cardboard tank that we pulled across the front of the range. With Tracer, it gave an indication of where the round would go in an anti-tank role. It was a good training exercise, and after we zeroed the Bren to the sight, it was fairly accurate. The big thing was that it gave the Gunners an idea of leading a crossing tank.
We tied a ball about 8 feet in front of the target tank, and used two pulleys, the first one being open at the top. This first one was at 90 degrees to the front of the range and the second one being about 20 feet parallel to the side of the range. In practice, there was a long "haybale twine" cord that a guy slightly behind the gun could pull to move the "tank" crossways for about 50 feet, then the ball would hit the first pulley and disengage, thereby "stopping" the tank for a bit while the slack in the twine was being gathered in. When it became tight again, the "tank" then changed to about a 35 degree angle and continued. The second pulley was big enough that the "ball" passed through it.
The "gunner" then had to earn his privilege by going downrange and retrieving his tank target, replacing it with another cardboard cut out, and resetting the carriage and line on the pulley.
I can see the value of mounting a bren loaded with tracer on a Bofors. It would help train a gun crew for lead and elevation when they could see where their rounds were going.
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