I overlayed it on top of original photo from this post, and I think the lower barrel is off. I made it bigger than the top one, but it looks like they should be closer to the same size. I could try to fix it, but I'm going to wait a little while longer and see if anyone will end up posting flattened pictures. If not, I'll give it a go at doing it myself again with a different picture.
View attachment 211587
As for the scale, whoever said further up the page to measure the distance between the holes on the cassette tape is absolutely right. That's what I did to try to get mine to the right size, but since my picture was off the entire size of my gun was off. If I have some more spare minutes at work I'll try to post an updated drawing of the gun some time today.