Determining safe loads for Cannons and mortars

[Double D]

George is always sending me PMÂ’s letting me know that I failed to dot an I or cross a T.    A day or two ago he sent me a message pointing out in a reference I made about determining safe loads that there is not 480 grs. Av. in an ounce.   Yep you are right George.  As I recall that info came from the linked source.   When I went to the linked source to confirm, lo and behold the link doesnÂ’t work.  So here is the correction and it no longer contains the reference to avoirdupois weight.  

National Safety Rules and Procedures
for Shooting Muzzleloading Artillery, as adapted by the American Artillery Association March 2000

1. Powder charges should not exceed 2 oz. of Fg or 3 oz. FFA or Cannon Grade Goex powder per inch of bore diameter. No excessive charges. Use black powder only.

2. Prepare powder charges in advance using heavy duty aluminum foil. Baggies may be used inside the foil, taking care not to allow excess air in the baggies and removing excess plastic where unnecessary.

While working on the update I also found that the there is a difference in the safety rules from the various Cannon shooting groups.

Artillery Safety A service of The Civil War News: New Black powder Regulations January 2003.

1. Maximum blank powder charges for properly constructed guns of 3-inch bore or larger should not exceed 2 oz. of Fg grade or 3 oz. of Cannon Grade GOEX black powder per inch of bore diameter. Maximum powder charge for bore of more than 2 inches and less than 3 inches should not exceed a total of 3 oz. Fg or 4 oz. Cannon Grade. Use reduced loads with projectiles. (See North-South Skirmish Association regulations for a guide to projectile weights and powder charges.)

2. Prepare powder charges in advance using light-weight plastic baggies with end twisted closed. Leave 2 inches of twist; cut off excess plastic. Fold twist to bag. Enclose bag in a triple layer of double-thickness heavy-duty aluminum foil (six layers total). Take care not to break plastic baggie. The bag prevents escape of powder dust and keeps granules from getting trapped under folds of aluminum to help insure complete burning. (Aluminum foil wormed out after firing often yields unburned powder although this may appear impossible to those familiar with smaller caliber guns.)

Both sites make reference to blanks

AAA says:

9. No wadding shall be used at any time. This includes firing blanks.

Besides the distinct reference in Rule 1 CWN says:

10. When blank firing no wadding should be used nor should be necessary for a realistic report.

I will update the FAQÂ’s and ad an FAQ for blanks.

For the record, although it no longer appears in the rules all weights are avoirdupois.  And yes George that is 7000 grs. to the pound, 437.5 to the ounce.

[Squire Robin]

I don't yet understand the mechanics of making the boom.

If I light a pile of powder it goes whoosh, if I pour it in a gun it goes boom, but why?

I understand that at the bottom of a cannon it is constrained, it can't go up, down, left, right or back, it can only go forwards. But surely if I put a little pile of powder at the bottom of a cavernous bore it will whoosh.

There must be a boom threshold, something changes as the load increases to cause detonation?

Does it still go boom if you light it from the front?

Puzzling

Squire Robin

[Double D]

Robin,

I don't know why it goes boom instead of woosh, must have something to do with the confinement and the pressure being  forced directional.  I also think that loading it contained in a cartridge versus loose in the bore has something to do with it.

Your guns are  6 PDR so the bores should be  3.67 inch.  Weigh out 7.34 oz of FFG  or 11.06 oz. of Cannon grade powder put it into a cartridge and load the cartridge into your cannon, no wads and fire them as blanks.  You will get plenty of  noise and it will sound like a cannon and not a explosion.

Go here to learn how to make a cartridge Loading Cannon Cartridges

[jeeper1]

Even a partial containment causes a serious boom. A story as an example.
Many years ago, 33 IIRC, I was showing a friend the different burn rates between smokeless and black powders in the open air (actually the floor of the garage).  My friend was impressed with the amount of smoke put out by the black powder. He wanted to see if he could direct all of the smoke straight up to see if it would form a mushroom cloud. so he put a tablespoon of 3F on the concrete and then placed an empty cardboard tube from a roll of TP over it, inserted a piece of cannon fuse, lit it and stepped back about 10 feet.  When that powder went off the rest of the family thought we had blown up the garage it shook the house so bad. I don't remember what happened the the cardboard tube because the lecture from my father was a bit more important.

[Double D]

I don't remember what happened the the cardboard tube because the lecture from my father was a bit more important.

Been both the reciever and deliverer such lectures...I used my fathers words with out credit, as to do so, would have been admission of commiting similiar stupid acts.  Just don't tell my kid...he's 39 yoa now and I hope hasn't figured me out.


I do think you are right that containment has some thing do with the report.

Just make a tin foil cartridge, poke a hole in it and add a fuse and light and see what happens. It won't be whoosh.

[GGaskill]

I think it works like this:  
I think we all accept the idea that the expanding gas has to reach the open atmosphere in a relatively high pressure state to cause a concentrated sound wave (the boom.)  Clearly the inertia of the shot provides the resistance to the expanding gas to keep the pressure elevated until reaching the muzzle.  But anything with mass can provide that inertia--a wad or even gas.  In a blank shot, the rear portion of the charge is accelerating the mass of the front portion of the charge (note that most blank charge recommendations use about twice the powder of a shotted shot) plus the mass of the air occupying the bore prior to the shot.  The boom is that rear portion of the charge escaping the confinement of the bore and the inertia of the front portion plus the air just as in a shotted shot.

[Squire Robin]

But anything with mass can provide that inertia--a wad or even gas.

Brilliant :idea:

Once the expanding gas exceeds the speed of sound it can't push the air out of the muzzle slowly, it must gather it all into one lump which will push back with ever increasing force.

I can go for that. To get a boom the hot gas must reach or exceed the speed of sound :-D

[Double D]

(note that most blank charge recommendations use about twice the powder of a shotted shot)

Actually that is only a little correct George.  If you check the references at the top of this thread you will see the recommendations for blank charges. They also call this the maximum load for the cannon.  Loads for projectiles are developed by reducing these loads.  They may be reduce by half or more- or half or less.  

If the shotted load was half or more doubling the shotted load would be an overload.

Switlik states that the blank load can be up twice the ball load as long as no ball or wad is used. Switlik also says  a "satisfying blank load" can be made using substanially less powder if FG is used. Switlik says if a wad is used that the area 1/4 mile down range should be cleared of people or "damageable  property".

Since Switlik was a consultant on the writing of the above rules I think we can safely say that blanks can be double the shot load as long as no wad is used and it doesn't exceed the recommendation in the referenced safety rules.

Those rules were created by long time cannon shooters both from research of the original Ordnance manuals and from years of practical shooting experience and testing.  Since it is a matter of safety, I can see no reason to ignore their recommendations.

Just a note for guns smaller than 2 inch use the chart found in Appendix 1 of Switlik's book to determine maximum load.