Will My 12 Ga Breech Loading Blank Firing Cannon Be Illegal?

[Mark 42]

I couldn't decide if I should post this in the 2nd Ammendment related
forum or the Blackpowdre Cannon forum... I ended up here.

I started building a 12 gauge naval cannon from various pipe
lengths and a resizing die found at a Boeing surplus store
(.810 bore w/ 3/8 to 1/2" wall thickness for the breech area).

I don't want to go into too much detail about the cannon, you
can see some of that at this URL:
http://sj24.net/phpBB2/viewtopic.php?t=451

It is not pretty... I haven't got my shop set up yet, and
it's just some tinkering at very low tech levels. It will
end up nicer... even though I'll be using a die grinder,
4-1/2" angle grinder and 7" disk sander to finish the
outside surfaces by hand (along with hand files and emory
cloth).

I'm more interested in a recent discovery from my research in
pursuit of some good drawings of a naval cannon carriage...
it appears that the BATF may not look favorably upon a
12 gauge cannon if it fires shotshells. My plan is to
use empty casings with a new primer, filled with blackpowder
and a cardboard disk. But, I'm starting to wonder if I wll
have to go to a simple muzzle loader (I intended to make
a second breech that had a match hole for using it as
a muzzle loader, for times when ceremony is desirable).

Do I need to forget the 12 gauge blanks idea altogether?

Here's a thread about breech loading cannon issues.
It almost ended early on when it turned out to be a qustion
from a British subject, but it later continues into a discusiion
about the U.S. policies on breech loading cannon.

http://www.chaski.com/cgi-bin/machine_archive/webbbs_config.pl?read=84266

And this one (Below) seems to imply if I were to go to 10 Gauge instead
I would be okay. My bore (.810) is already bigger than 10 Gauge (.775),
so I would only have to enlarge the chamber bore a bit... I'll have to
get some 10 gauge casings to measure the OD at the base since I haven't
found much data from more than one source or from a trustworthy source.

http://www.graybeardoutdoors.com/phpbb2/viewtopic.php?t=67262&sid=fd4b2ec02d2dcc93f6e93990b7b2815b

I checked the FAQ (URL Below) but I'm still a bit unsure about
the legalities involved.

http://www.graybeardoutdoors.com/phpbb2/viewtopic.php?t=16901

So, how is it that making a 12 gauge salute cannon illegal is not an
infringement upon my right to keep & bear arms?

If I made the barrel 18-3/4" long (It's around 15 now) would that
allow me to just call it a shotgun, even if I mount it in a naval cannon carriage?

I'd love to hear what y'all have to say.
Thanks,
Mark Kanzler

Here are a few relevant links:

Cannon Plans (I'd like to find a free top view drawing like the
one at the second URL):

http://jerry-howell.com/1779.html
http://www.ussconstitution.navy.mil/xlongguns.html

Bore diameters:
http://www.globalsecurity.org/military/systems/munitions/12.htm

A Source for blanks (probably not the cheapest):
http://www.cannon-mania.com/ammunition.htm

I did find some info on chamber diameters, but I measured
a 12 gauge as .810 which is larger than what was in the chart below,
so I'm not sure the 10 gauge value is trustworthy or not.

http://www.tbullock.com/bpsg.html

Forward Chamber Diameters
Gauge   Inches   mm
.410   0.463   11.76
28   0.614   15.60
20   0.685   17.40
16   0.732   18.59
12   0.798   20.27
10   0.841   21.36


Some text validating my .810 chamber diameter measurement
(taken at the metal portion at the base of a shotshell):

http://www.findarticles.com/p/articles/mi_qa3623/is_200411/ai_n9460038#continue

[Graybeard]

Wrong Forum. I'm moving this one to the Mortar and Cannon Forum where the folks who know the answer hang out.

[Mark 42]

Thanks.

I wasn't sure.

[GGaskill]

None of us here can speak for the ATF.  Your best bet is to write them with a description of what you want to do and see what they say.  Don't say you have already built anything. 
 
There is an outstanding inquiry on this subject by a board regular but I haven't seen anything saying he has received an answer.
 
Making the barrel alone 18"+ would not make it a legal shotgun.  There is a minimum overall length requirement, too.  But I would think the carriage would qualify as adding the additional length if it were long enough.
 
I have a drawing of the Constitution 24 pounder carriage that is believed to be correct.  However, about the only additional info you will get from a top (plan) view are widths.  If you can read .dwg files, I can email the data to you.

Also check out this thread about a 12 gauge salute gun and this thread about the legality of it.

[Double D]

I can not emphasize strongly enough listen to what George says,  do not build that 12 guage signal gun until you submit plans to ATF and and get a return approval from them to build.  

There are a lot of good cannon designs around that you can build with out running a foul of othe Feds.  If  you are into Artistery, take a look at George's 24 PDR, it is beautiful!!!

By the way welcome to the board!

[Cat Whisperer]

None of us here can speak for the ATF.  Your best bet is to write them with a description of what you want to do and see what they say.  Don't say you have already built anything.  
 ....

EXACTLY RIGHT!

When they respond you will KNOW one way or other (IN WRITING).
That helps you sleep at night!  

Since these guys are the ones that would come and pick you up having authorization from them carries a lot of weight.  (Note that I am side-stepping ALL the logic and arguments for and against ALL of the issues.)

Cut to the quick - ask.


AND welcome to the board!  It looks like you've done some research already on this.  Look through the legal discussions here, identify the issues so that you know what you think is legal and go for verification from them.  A couple of the issues are the ability to chamber readily available ammo and/or if it's a signaling device as opposed to a shootin' iron.

[Mark 42]

Thanks for the welcome and the info so far.

I'm sorta trying to find a simple way, like go to a gauge (caliber) or barrel length that is always considered legal for firing shotshell blanks.

Or if going with a muzzle load configuration will make it legal to build and
fire a blackpowder cannon with blank loads (probably a wad of tinfoil
as a "cannon ball".  I also wonder about muzzle loading blackpowder
cannon used to fire projectiles like a wine cork that fits loosely
into the barrel... or golfballs or small rubber balls (mini superballs).

It just seems like handloaded 12 gauge blackpowder blanks would
be a simple and safe approach - no worries about the hazards of muzzle
loading (I know they are not big risks... I have a .45 cal Kentucky Long
Rifle).

I'm asking before I finish the project for the reason y'all alluded to above...
once it's finished I would be in violation of the law if I built the wrong toy.
(I know it's not really a toy and the potential lethality if used wrong).

You can see where I'm at so far in the pictures at the URL below:
http://sj24.net/phpBB2/viewtopic.php?p=571#571

So far it's just an ugly looking tube of varying outside diameters.

It never really occurred to me that a blank firing cannon could be
trouble if I don't ever use it to fire projectiles (even one that is
capable of firing projectiles)

It just strikes me that people are making muzzle loading golf ball and
bowling ball mortars & cannon... and then a simple 12 gauge one is
illegal because it uses a cartridge (blanks only even).

A piece of pipe with an adapter to go from 3/4" to 1/8" NPT and
a 1/8" NPT nipple with a nail in it would make a simple and dangerous
shotgun that would be legal until someone figured out why the nail
fit nicely into the 1/8" pipe section.

My point is that, as usual, the laws seem arbitrary to me, and make
little sense. With a breech that has to be screwed on, my cannon
would be a single shot device (slow to reload).

Also, there is no way that I will spend the $200 for a special license,
so I really am looking for something I can build without getting into
trouble if I don't go to great lengths to get approval beforehand.

One option I'm thinking about...
My understanding is that a person can own a gun and also can own
parts to make it into an illegal fully automatic weapon... as long as
the parts are never installed.
In the same spirit, I could build the cannon with the screw-on breech
(removable) that has a touch hole and no firing pin or hammer mechanism
(no mechanism whatsoever that would make it discharge center or rimfire
ammunition).
Then make another breech that has all the workings to make it a center
fire discharging mechanism (like a hammer & firing pin or spring
loaded firing pin).
As long as I don't put the firing-pin breech on until after I get the right
permits or permissions, I should be okay (by similarity of precedent law).

But even that could be dicey, I think... and I probably would save the firing
mechanism project for farther down the road.

At least stumbling into the issue today has possibly saved me from
a costly mistake. It's a shame that we have to ask permission for
harmless activities simple because they have potential to do harm
when in the wrong hands. Any further comment I might make (biting my tongue)
would be better said in a forum discussing the 2nd ammendment.

Anyway, keep the ideas coming. I promise to take them with a grain
of salt until I verify them with authoritative sources.

But I would like to know what I can build without need for anything
more than the tools and materials to build and fire it (in other words,
no permits or special licenses or jail time)

Click the picture below to see what got me inspired
(again) on this project... [/color]
actually I have wanted one since I saw a "Big Bang"
carbide cannon as a kid)[/b]

[Cat Whisperer]

Mark 42

You REALLY need to read the law, as much as it may not make 'common sense' they are the statements by which those folks that govern us will or will not allow us to do what we want to do.

Look through our 'sticky' referneces - noteably FAQ's (if I recall correctly) there is a link directly to BATFE's section of the law.

You're playing with "$10,000 and or 10 years" for each offense.  This is not trivial.  Three of us have given you some very good advice on how to go about it.  Don't Panic, just go to the 'Guide' and learn the rules of the game.

[Mark 42]

I'll keep researching.

I did read the FAQ (quickly) and will re-read it more carefully, and will continue
to learn. I'm kicking around some ideas, and asking impressions,
but don't think that I won't look in more depth as well.

I did find this:
http://bronzecannon.com/black_powder_cannons.htm

(it's a British site, but BATF is an American reference, I think,
so I'll be checking if it refers to U.S. laws like I think it does)

      LEGAL ISSUES on Antique and Black powder cannons.

 Firearms in this country, particularly those deemed to be “destructive devices”, are tightly regulated by ATF (Bureau of Alcohol, Tobacco and Firearms). The question becomes: is a cannon a destructive device? According to Federal Regulations, a cannon that is “not capable of firing fixed ammunition and manufactured on or before 1898, and replicas thereof, are antiques and not subject to the provisions of either the Gun Control Act of 1968 or the National Firearms Act of 1934”. Fixed ammunition refers to a projectile and powder charge than can be loaded as a single unit. By this definition, even a percussion primed breech loader is exempt if the powder and shot are loaded separately.

I'll keep researching too. I see 10 Ga.  blank firing cannon for sale, and that
interests me, but I won't build one until I am sure I can do it legally.

I have firearms, and would not want to jeapordize my right to own them
by getting a weapons related conviction against me for owning the
wrong "toy".

I'll heed your advice, but I also want to get a few general impressions
and some overview information (it'll help me know what to research
a little).

[Cat Whisperer]

 ....
      LEGAL ISSUES on Antique and Black powder cannons.

 Firearms in this country, particularly those deemed to be “destructive devices”, are tightly regulated by ATF (Bureau of Alcohol, Tobacco and Firearms). The question becomes: is a cannon a destructive device? According to Federal Regulations, a cannon that is “not capable of firing fixed ammunition and manufactured on or before 1898, and replicas thereof, are antiques and not subject to the provisions of either the Gun Control Act of 1968 or the National Firearms Act of 1934”. Fixed ammunition refers to a projectile and powder charge than can be loaded as a single unit. By this definition, even a percussion primed breech loader is exempt if the powder and shot are loaded separately.

....

You're on the right track!  Note the word 'replica' and before 1899.  Cartridge loading is an issue.  AND somewhere in there (I think) is something that draws a line between a firearm (of whatever class) and devices that are used for safety or signalling purposes.

You've got the right attitude!  The question will always remain - how does the BATFE interpret what you're proposing in context of the way they interpret the law.

Drive on!

[Double D]

We have a very strict rule on this board. We don't debate the rule, we let ATF tell you what is legal and what is not.  You will not be able to use any advice as to legality  posted on this board as an affirmitive defense in a court of law.  

We allow discussion of the following cannons only:

Muzzleloading cannons not capable of firing fixed ammunition and manufactured in or before 1898 and replicas thereof are antiques and not subject to the provisions of either the GCA or the NFA. [26 U. S. C. 5845, 27 CFR 179.11]

We will also allow discussion of cannons that you post a letter from ATF saying it meets the above ruling.  Right now, unless you can provide a letter from ATF saying a 12 guage cannon is considered a replica cannon, we ask that you not  discuss it here.  Doesn't matter if you intend to just shoot blanks, it still uses fixed ammo and not allowed here with out an ATF letter.

We do this to protect you and to protect us.  We do not want you to become the prey of some new rookie ATF agent trying to make his name by cruising this board.  The Veteran Agents are out looking for real criminals.  We also don't want it to appear that we are aiding and abetting you in breaking the law.  I intend to retire to Montana not the Federal Pen.

We also do not want to be seen as giving you legal advice...we aren't lawyers.  If you have questions about the Gun Control act go here: http://www.atf.gov/firearms/faq/faq2.htm#m28 .  

This board also isn't about debating the propriety of the Gun Control act.  Take that somewhere else.

With that bit of nastiness out of the way, what we will discuss is building and shooting cannons safely.

Or if going with a muzzle load configuration will make it legal to build and
fire a blackpowder cannon with blank loads (probably a wad of tinfoil
as a "cannon ball".  I also wonder about muzzle loading blackpowder
cannon used to fire projectiles like a wine cork that fits loosely
into the barrel... or golfballs or small rubber balls (mini superballs).

Look around our board a bit and you will see that we shoot all kinds of objects including lead and zinc balls.  We just had a golfball mortar contest and had some really neat little guns posted.  

We are safety minded and would not consider a wad of tinfoil as a wad for a blank load.  In fact wads of any kind are not recommended for blank  loads as the wads become projectiles and can cause injury and damage.

In the same spirit, I could build the cannon with the screw-on breech(removable) that has a touch hole and no firing pin or hammer mechanism (no mechanism whatsoever that would make it discharge center or rimfireammunition).

If you built  it too look like a pre 1898 cannon no problem.  But if you use seamed water pipe as you seem to suggest,  it would be unsafe.  Water pipe especially seamed water pipe is not strong enough and can and will burst.  If you used seamless tubing and a solid pinned in screw in breech plug of the proper design, it would be fine.

Then make another breech that has all the workings to make it a center fire discharging mechanism (like a hammer & firing pin or spring
loaded firing pin).

Actually many cannons had just such a firing mechanism. The hammer or striker ignited a primer and that ignited the powder charge.



I suggest you go to the top of this forum and look at our post Where to find Blackpowder Cannons and shooting supplies

You will find lots of neat Ideas for cannons there

[Mark 42]

I'll do my best to abide by the forum rules. Sorry if I stepped outside
of them. :oops: I won't construe anyone's advice here as authoritative, and
won't rely on iformation gleaned here as a primary source.

So far, It looks like if I build it as strictly a muzzle loader, and make it a reasonably
close replica of a 24 pounder like the ones on the USS Constitution, I won't
have any problems.
I'll double check on that before I close off the breech of my little cannon.

The difficult research is going to be what deviations from that exact configuration
would still leave it a legal cannon replica.

I am still curious about the 10 ga. cannons (seen 8 ga. too) that are
commercially available... maybe it's considered an obsolete cartridge.

I'll probably just build it as a muzzle loader, and then order plans
for the 24 pounder and do another one in the future... one that is
more finely crafted.

Part of the reason I began the current project was because I found
the resizing die and an extremely heavy walled hydraulic fitting to
make the breech from. That got it started, and since the dies were in various
sizes, I just chose one which a 12 ga. shell fit nicely into.

But for now, I want to keep working on the outside of the barrel,
and will hold off on the 12 (or other shotgun) gauge idea until my next
cannon, if there ever is one.

I'll begin it by contacting BATF and getting the appropriate permissions
(which, because of expense, would only make sense for a nicer cannon).

I did use a pre-made pipe for the barrel forward of the breech section,
with another pipe sleeved over it and brazed to it along the faying
surfaces. I think I have about 1/4" minmum wall thickness  for all but
the last 3" (near the muzzle end).

Since I won't be firing projectiles, I think even with a seam the pipe
should be strong enough, but I'll double check the remaining pipe
to see if it is seamed (I don't think it is... I got it at Boeing surplus).

When I look how thin the wall on my shotgun is, I would think that
for a similar sized bore and charge of blackpowder I am well over
built and should have adequate stress margins. (Comparison to 12 gauge
doesn't imply I'm still thinking of making a breech loader, it's just
for scale comparison).

If I have to scale back the powder to 70 or 80 grains for firing
a loose fitting wine cork, that should be a light enough load, I would think.

[Double D]

I am curious about the 10 ga. cannons (seen 8 ga. too) that are commercially available... maybe it's considered an obsolete cartridge.....
I'll begin it by contacting BATF and getting the appropriate permissions
(which, because of expense, would only make sense for a nicer cannon).

If you get an answer about the signalling guns in 12 guage and 10 guage from ATF, please post the letter for all to see.   We would like to hear the answer.

[GGaskill]

Actually a permissive letter from the ATF is without charge, to my knowledge.  The special licenses are what you have to pay for.

[Cat Whisperer]

Mark 42 -

You're headed in the right direction.  DD spelled it out and put some real effort in making it clear - your and our protection.

Look into whether or not the blank firing cannons will chamber a real 8, 10 or 12ga shell.  That may be a decision point.  Further, I've seen some with a rod going across the muzzle - which I wouldn't do even for a blank firing device (personal sanity) - which may indicate to someone that it would be only for blanks.

Read the other folks' posts on submitting designs to BATFE - there is some really good background material there.


It may help to go from a known 'good design' that you know is legal and work one point at a time towards the design of your interest.

Sorry for not giving you a simple answer, but life isn't.

DD has given you some VERY mature and experienced advice.  Read his post very carefully - it was written with deep concern and years of experience.  AND keep us posted on what you learn/hear from BATFE!

[Cat Whisperer]

Actually a permissive letter from the ATF in without charge, to my knowledge.  The special licenses are what you have to pay for.

Agree.

The 'letter' is their written response to  your query.

FFL's come in several categories.

SOT is a special occupational tax for FFL's dealing in certain professions.

AND there are Transfer taxes for categories of 'Firearms' (legal definition) that we do not discuss on this forum as we have set out in the Rules of the Forum.  For reasons well explained by DD.

[Double D]

The difficult research is going to be what deviations from that exact configuration would still leave it a legal cannon replica.

As long as it more less looks like a cannon of the era you won't have a problem.  You don't have to have a precise correct replica, as long as it's close.

Since I won't be firing projectiles, I think even with a seam the pipe
should be strong enough, but I'll double check the remaining pipe
to see if it is seamed

The ability to hold pressure is only part of the problem.  The other problem with seamed pipe is that black powder fouling is forced under pressure in micro pores of the welded seam which can and will slowly rot out and burst.  Remember the warnings about shooting Damascus shotgun barrels. Same principle. Besides water pipe is just dead soft, forget it, we'll help you do better.

When I look how thin the wall on my shotgun is, I would think that
for a similar sized bore and charge of blackpowder I am well over
built and should have adequate stress margins. (Comparison to 12 gauge
doesn't imply I'm still thinking of making a breech loader, it's just
for scale comparison).

 Two different types and strengths of steel.  Forget the water pite, it's just to dangerous.

If I have to scale back the powder to 70 or 80 grains for firing
a loose fitting wine cork, that should be a light enough load, I would think.

Why bother with a cork, you don't need it. We can aslo find a load for you.  

Why build a blank gun.  You may have no place to shoot projectiles now, but who knows what the future holds.  You can always fire blanks in it until you get the chance fire projectiles.

[Powder keg]

Hi, One important thing here. Water pipe is for WATER! Also, plan on building something that you would let your mom shoot. Just because it's considered legal dosn't mean it's safe to shoot. Many of the things we build will be around a lot longer than we will and we don't want anyperson in the future getting hurt.

Be safe!!

[jeeper1]

Mark42 earlier you wrote

One option I'm thinking about...
My understanding is that a person can own a gun and also can own
parts to make it into an illegal fully automatic weapon... as long as
the parts are never installed.

You are so wrong. Mere possession of the parts is a felony.

[Cat Whisperer]

Mark 42 -

Stick with it.  You're in good hands here - the folks here care about being safe and legal very much.  There's a lot to be said for your enthusiasm - and we enjoy the discussion.  Don't ever think we're getting down on ya.  Our responses are about issues that would do damage or incarceration.  And if you post a picture without an empty powder can in it for scale the thread may go on forever noting the fact.  

You will note that even though I've made a few mortars that I have a lot to learn - that's one of the reasons DD & I started this forum.  When I post pictures of how I do it you will often find that I'll point out how I wouldn't do it again.  What's even better is when other folks point out what I could have done better - that way we all learn.  It's a fundamental principle in the academic profession - peer review of your work is very healthy.  You'll see the same principle in our legal system - 12 honest men.

Be safe, be legal, be polite and have fun - the four requirements I have about what happens here.

[Will Bison]

Hi Mark;

I'm in total agreement with what the others have said regarding a breach loading device. My experience with ATF has always been positive and a simple letter along with some drawings and dimemsions will get you an answer. Be sure you state your intended use of the end product. If the ATF folks need more info you should get a letter from them pretty quick.

Exemptions for cultural, archaeological, historic and scientific reasons are generally not a big deal.

Good luck.

Bill

[Mark 42]

Just touching base with y'all.

I'm geting more & more motivated to write a letter to get an answer from BATF directly.

First I have to create some drawings of what I want to build. That'll also let you see more detail of what I have started (it's just a tube right now, no potential for shooting it so know BATF issues at this stage of build).

Basically, the first 4" have 1/2" wall thickness (Solid steel). The next 3" have 3/8" wall thickness, solid steel.
The next 3" have two heavy wall pipes, one inside the other, brazed together (like sweating copper pipe, but using brass instead of solder and with steel pipe) for about 1/4" wall thickness. The next 3" is the continuation of the inner from the last section with and EMT sleeve. The last 3" is just the inner pipe sticking out past the sleeving. The last 1" is part of a galvanized adapter just to give the flared muzzle slipped over the inner pipe.

Where the sleeve is brazed, it is also welded at each end.

So the first 7" is solid steel. The next 4" is doubled 1/8" wall pipe brazed together.

Somone mentioned the issue of corrosion in the seam weld. I haven't verified if the pipe is or is not welded. I got it from Boeing Surplus, so it probably is not water pipe... the only water pipe used is the flared end at the muzzle. But I'll be brazing the entire bore and then re-drilling it to get a smoother finish. It seems like if the welded seam is done correctly there should be no inclusions or pitting opportunities. I could magnaflux it, I suppose.

I figure the firing chamber is well overbuilt, and the rest should be plenty strong when you compare it to my shotgun's barrel, or some of the muzzle loading rifles (not including the octagon barrel of my Kentucky Long Rifle... it is not thicker, but is solid steel and about 1/2 the bore diameter).

If I have any other worry I might go ahead and put a steel sleeve inside the whole thing, but that would decrease the bore by at least 1/8" from whatever diameter I enlarge it to in order to insert the sleeve.

But I figure once the charge begins moving down the barrel 7 or 8 inches the pressures will already have begun to drop, especially with no projectile (though I would be tempted to shoot wine corks or aluminum foil balls).

I'm still doing a lot of research on stuff like chamber pressures and material properties.

[Cat Whisperer]

....
Somone mentioned the issue of corrosion in the seam weld. I haven't verified if the pipe is or is not welded. I got it from Boeing Surplus, so it probably is not water pipe... the only water pipe used is the flared end at the muzzle. But I'll be brazing the entire bore and then re-drilling it to get a smoother finish. It seems like if the welded seam is done correctly there should be no inclusions or pitting opportunities. I could magnaflux it, I suppose.
....
.

Welding will leave some porosity, into which the products of combustion (water and sulpher to name two) will seep.  From that you get corrosion and weakening.  The only way to avoid it is not have any welded area subject to the products of combustion - there are several ways of doing that.

Keep up the chase!

[Mark 42]

Okay, so then the issue isn't that a weld is a line of weakness along the seam,
but rather that it is a place for impurities (some corrosive) to get into the metal and create stress concentrations/risers (if I understand what I've read above).

If that's the case, then I don't necessarily need to start over with solid steel or seamless (extruded) tubing, IF I protect against impurities impregnating the metal.

So, I could do something like powder coat the bore (adding the thickness of the coating to the pre-coated bore diameter).

Or perhaps plating the bore with something like nickel or some harder or more inert metal.

Or sleeve the bore with a thin wall tube of something like titanium, using epoxy between the sleeve and the rest of the barrel to seal the faying surfaces.

I know that what I have now may look ugly, but it won't be as hard as some might expect to gring the outside to a reasonably nice finish, so I'd rather not start over.

My lathe is not big enough to do a decent sized barrel, so I have to do a lot of the work by hand. With a little creativity I can probably use my lathe (like making a wooden dog to drive the part with a faceplate and center).

BTW, from my research so far it's starting to look like breech loading isn't the issue, it's more a matter of if I use a cartridge load that I will get into trouble.

So I can make a removable breech (for cleaning) with a touch hole or a percussion nipple or even flint lock and use it as a muzzle loader (it'd be no easier to breech load it). Later if I get permission to, I can make another breech for the 12 Ga version (or 10 Ga if needed for permission).

I still like the safety and convenience of a shotshell blank, and I'm looking for visual authenticity rather than functional accuracy (a scale model of a 24 pound naval cannon from the 1700's similar to the USS Constitution's guns).

I'll build the muzzle loader, and will contact BATF to see if adapting or converting it to use 12 ga. blanks would be permissible.
I'm also watching the other message thread to see what the outcome will be, and to get info on how to contact BATF and what info they will want.

Maybe I'll draw the whole thing in CAD and make drawings from the 3D solids.

Oh well, there's no rush... there are a lot of higher priority projects on my list anyway.

[GGaskill]

Take a look a this Building a 24 pounder thread for both the wooden lathe dog and the machine work (nothing wrong with wooden lathe dogs.)  It's progressed beyond this point (see the Building a 24 PDR Graybeard thread for more recent pictures.)

[Double D]

If that's the case, then I don't necessarily need to start over with solid steel or seamless (extruded) tubing, IF I protect against impurities impregnating the metal.

So, I could do something like powder coat the bore (adding the thickness of the coating to the pre-coated bore diameter).

Or perhaps plating the bore with something like nickel or some harder or more inert metal.

Or sleeve the bore with a thin wall tube of something like titanium, using epoxy between the sleeve and the rest of the barrel to seal the faying surfaces.

Were it so simple then experts like Switlik  and N-SSA wouldn't be telling you to use seamless tubeing.    You have to deal with keeping your coating whole and not pierced and the issue of high pressure micro impregnation plus high temperature condensation.  Their recommendations are based on many years of study and experience.

Bottom line welded pipe is not safe for cannons.  Welded tubing may be stronger and can be used require extra precautions but why take the chance go with the solid.Bursting cannons are ugly things...read the cannon accident post at the top of the board.

[CU_Cannon]

Or perhaps plating the bore with something like nickel or some harder or more inert metal.

I'm not sure that plating a bore would be a great idea.  The coating is extremely strong and tough but brittle.  If a crack develops in the plating it would then start to translate into the sub-metal weakening the bore and allowing corrosion.

[Mark 42]

If the innermost tube (in a config consisting of layers of sleeved tubes) is not welded, but one or two of the outer ones has a welded seam, it would
at least meet the corrosion resistance.

Plating tends not to be very thick (electroplating at least), and probably would
not be impermeable for very long.

I could slide a thin walled brass tube into the bore, if I find
the correct size.

I don't really want to throw away what I have done so far, so I am trying to come up
with ways to correct it if I find that the tubing I used does have a seam.

[Cat Whisperer]

....
I don't really want to throw away what I have done so far, so ...
....

I will often build 3 or 4 tubes to see how they look or fit together with other stuff.  Build it, get what you can from it and move on.

Often starting from  a fresh piece of solid stock is the easiest way to getting what you need - the simpler it is the easier it is to get it done.

[Mark 42]

For now the project is on hold while I convert from flux core to MIG welding
(I have to wire in a solenoid valve and hook up the inert gas kit, and will
add a cooling fan to the welder while I have the covers off).

I don't have a lathe big enough to work from solid stock right
now, which is why I'm using various thicknesses of sleeving over
a core tube to approximate the taper and other diameter variations
of the barrel. If I can't show that the barrel is safe (by inspection,
test, or verifying what it's made of is suitable) I'll probably fire it
with no projectile a few times and use it for static display.
I can always fire it from a safe distance using a rocket (Estes)
igniter and wiring. I have some rocket igniters in a drawer in
my hobby shop.

I can also reduce the bore and put a new (seamless) inner tube in it...
maybe .50 or .69 cal... I could also ream the current bore quite a bit
and put in a new inner tube.

I'm chomping at the bit wanting to work on it, but I spent the last
two days racing sailboats, and am committed to race again in
a couple of weeks, and have a motorcycle that hasn't been safe to
ride for a year, and several wiring issues on various vehicles...
and of course many other tasks waiting for attention.

At least I finally put together my bicycle which I started to
overhaoul a year and a half ago... Sheesh, does it ever end?