Maybe the platform weight slowed down the rotational speed.
I read somewhere it could go about 60 degrees a second.
apparently these things are on the collector market. $25 K with dummy guns, $ 50K with semi auto and over $ 100K full auto.
Theres an article about the M45 on guns.com.
in that one, there's a photo of one at a show. They unlimbered the wheels when it was emplaced. It's hard to tell in your picture if that's the case. But I'm guessing yours will be in travel mode.
The Dragon painting also looks kind of silly on its little trailer firing.
Pawel the US is a wonderful place...