I have a theory about the reason the guns were built this way. Apologies if it's been mentioned before in this forum - I'm new. I've always wondered what was going on with the center-post on the prop.With in-universe practicality, it wouldn't work. I think I know why. The center-post (highlighted in orange) of the prop seems to go all the way down to the surface of the gun. The sketch designs don't. The gun couldn't pivot if it did. The reason I think this is for a lever and pivot to pass down the center-post so the gun can be pivoted up and down. Comparing the sketches with the set they appear to have moved a 'electronics box' from the end of the center-post to the back of the gun to hide this. This set-up, to me, justifies the way its made. Any opinions?
Another thing. Highlighted on the plan is a circular greeblie peice of the prop. That looks like the cap from a 44 Gallon oil drum, or something similar. My parents ran a service station (gas) when I was a kid and I realised that thing looked familiar.