I have decided that since I have gone this far that I am going to submit a form 1 and complete this as an NFA DD.
Especially since no one that I have talked to can tell me whether or no it will be considered a DD if I complete it where it could fire.
At this point it has NO chamber for any known fixed ammunition and has a 1.5" steel rod welded into the breech end of the bore. On top of that the breech ring is incomplete and there has been no breech block machined. Right now it is a 900lb paperweight.
I have muzzle loading cannons of the Civil War variety. I had given thought about making this one a breech loading black powder cannon. Fired by a .22 blank used in powder actuated hammers. If I take to to WWII events, a breech pug would be obvious when people look at it.
My idea would make it kind of like a big Civil War Sharps rifle. Insert projectile (or not) , insert powder bag, close breech, prime, and fire.
I asked a class 7 SOT if it would be legal like that, and he said it depended upon the agent who looked at it. I asked an ATF agent, they said they would have to ask the NFA folks. I sent the Firearms Technology branch a letter with detailed descriptions, measurements, and excerpts from the NFA rules to see IF it would be considered a DD.
I got a very polite reply that they could not make a determination through descriptions, drawings, blueprints, photos, etc. The firearm would have to be sent to them in WV for testing and that they were not responsible for any damage that may occur during testing. Also the rules say that if it was determined to be a DD that I could lose possession of it and it could be destroyed.
I've got too much time in it for that. I would cry for sure.
For me $200 is nothing to sneeze at for the Form 1, but it is better than legal issues and/or losing a project that I have worked on for 7 years (off and on).
The hang up is that the bore is over .50 inches. I imagine they could say it met the criteria for a DD, even though it would fire using pre 1898 style loads and ignition sources, i.e no fixed ammunition. Unless I cross drill through the bore and put rods through it for blank fire only, but what's the fun in that? If I go through the trouble of completing all the parts so that it will fire a blank, why not make it fire a projectile? I am not sure that I will live fire it more than a few times ever. Even then it will be by remote means from a covered place. However, If I decide that I want to shoot it, then by God, I want to be able to shoot it. 95% of what I would shoot would be blanks though. I am just not willing to remove the possibility of live fire if made to fire blanks.
If I am going to build this to fire then I about as well rifle this barrel so I can hit what that really nifty sighting mechanism that I made is aiming at. Soooooo I have gone and gotten my fingerprint cards, and getting the passport style photos printed. While I am waiting on the Form 1 approval, I think I am going to make a contraption to rifle this barrel. It is supposed to have 1 turn in 25 calibers. So 1.5 inches times 25 is one complete rotation every 37.5 inches. I can do that. It is supposed to have 12 grooves. I can do that. What I am trying to determine now is how to machine an adjustable carbide cutter that I can drag down this 6 1/2 foot long barrel and cut the rifling. It'll take a whole Saturday or possibly weekend to cut, index 12 times, then adjust the cutter and repeat until the grooves are 1/16" or 3/32" deep. I am thinking that the groove needs to be at least 1/8" wide.
Along the way, I am also going to have to machine a lead mold for conical point hollow base projectiles alone the lines of a Civil War Enfield bullet. I am not sure that the rings from a Minie' Bullet (Minnie Ball) are necessary. I'll cross that bridge when I get to it.
Again, this is one of those projects that I often look at and wonder "what was I thinking?"