Just to confirm.....
This barrel is a 25% size replica.
Also wondering what the internal hidden trunnion dimension and depth is?
I believe the actual scale on that drawing is 27%. Since the actual Napoleon did not have barrel wall thickness equal to the caliber, as is the safety standard we recommend, I scaled from the bore. We wanted an Inch bore gun. So I scaled from a 3 inches diameter over the breech and it came out to 27%. Read the entire thread for that detail.
The original Napoleon was a cast gun, the trunnions were integral. I do not know how Mike makes his trunnions and attaches them. It does appear he makes a recess in the barrel and makes two separate trunnions.
Photo courtesy Mike Elledge
You can see center mark and the two step trunnion- a rimbase that goes in the barrel and the trunnion.
Here is one way to attach trunnions.
As with most things this is just one way. This from a William Green Drawing of a small scale gun so don't use the dimensions for your gun. I used this method to attach the trunnions on my Inch model of the 42 PDR that was on the USS Cairo.
I made the rimbases interference fit. To turn them in place I used a rifle barrel wrench and a lot of muscle. I shot the gun a number of times. I went to a cannon shot in Northern California and when my gun was inspected one of the trunnion was loose and bent. I was required, if i wished to shoot, to have the trunnions welded in place.
Others will share their method of attachment to give you additional ideas. We have had a lot of discussion on this subject.
A good way to search our board is with this search parameter:
Copy everything in side the code box above and paste it into the search window on google. Then search. If you want to find something else just change the search word, like change trunnion above to Napoleon and you will get all posts on Graybeard on Napoleon. That trunnion search by the way has a lot of good hits for you to look at.