5" Diameter sounds fine, but would it be possible for the barrel to be maybe 36" instead of 24"?
Buying cannons (making them, too) is kind of like hot rodding and car racing (you know, speed costs money, how fast do you want to go?) So the answer to your question is of course! But it will cost more (and be heavier and harder to transport.) If you want a model of a real gun, the diameter is proportional to the length, so a 5x24 gun would scale up to a 7.5x36 gun, which is starting to get into some heavy metal.
...i tend to lean towards the 3rd one. It seems the most basic.
Number three is 4X24 and 1" bore (45 lbs barrel weight); it is a 1/5 scale model of a USS Constitution 24 pounder in the English style of 1779. The Dahlgrens and Brookes are about 75 years more modern (1850's, 1860's) and much simpler to make.
One can be a little less proportional if making a freelance design, but if you read some of our older posts, you will find more than one statement such as "when I built it, I didn't care about accurate replicas, but now I wish I had." So that is something to consider. The $150 estimate is for metal only; number three has about a hundred hours of now and then time in it (I've been working on it since late 2004), so figure a substantial labor charge if you have to pay someone to make one like it.
