Loading density in artillery?

[darkgael]

Hello, all. I'm just registered with this forum. Blame it on DD for inviting me to the Mortar shoot at Ft. Shenandoah.
I just read a post from another forum (BP-L at Yahoo) which gave me pause. The note says, in part, "the standard load for many breech loading BP artillery pieces intentionally filled only 70% of the chamber. This was done to reduce peak pressure in the artillery pieces." Is that accurate?
The note also says that max pressures with BP "are always less than 100K psi." True? Not?
In addition, the note states that BP "cannot detonate. It can burn really fast but cannot detonate" This is opposite what I have understood.

Please understand that there is no criticism intended here; these ideas are different than what I have believed. Maybe I need to read more.
I have sent the entire text to DD.
Pete

[Double D]

Pete,

Welcome to the board, glad we were able to get you interested in shooting cannons and mortars.

You have a golf ball mortar kit headed you way.  I raided my personal stock to get the materials.

Your questions are just fine.

I have already responded to you email but I will repeat for others.

Black powder is classed as an explosive and explosives detonate.  I don't know what maximum pressures are.  Not being a physist I'm not qualified to answer your question about  pressure.  We do have a couple of fellows here that may be able to explain.

In artillery the ball is always seated against the charge.  Cannons have windage.  That is the projectile in blackpowder cannons is always 1/40 of bore diameter smaller than the bore. This is to regulate pressure and assist loading.

Shooting cannons is not like shooting a big over sized muzzleloader.  There  is a completely different set of internal ballistics  involved.   Read up on cannon shooting before you acquire a cannon. Suggested reading is THE MORE COMPLETE CANNONEER  By M.C. Switlik with selected excerpts from other artillery manuals
The book can be order from these two suppliers.
The Complete Cannoneer from Matt Switlik[/i][/url]
South Bend Replica The Complete Cannoneer

Switliks book has safety rules for firing cannons and a discussion on pressure.

The rules can also be found at American Artllery Association.  You can also find rules on North-South Skirmish Association Skimishers page Click on Rules and a large PDF file with the rules will open.

[Cat Whisperer]

Pete -

WELCOME to the board!

You've posed several good questions.  Internal ballistics is one that requires some instrumentation for exact numbers, hence few people do much of it.

Detonation is a fast shock wave - correct (in my understanding) blackpowder explodes but does not detonate.

Peak pressure - takes measuring to do it, but blackpowder, perhaps because of the historical development of iron (lack of strength) is generally low pressure compared to smokeless powder loadings.  I would be surprized to see 100kpsi in blackpowder unless something is seriously overloaded (that is to say it is possible).

Glad to see that you survived the rain at Winchester.

[Will Bison]

I have worked with all types of explosives since the early '60s in commercial blasting and special effects. The air gap principle is sometimes employed to break rock. It ain't a good thing in 'shootin irons.

If a ball is seated away from the charge, the charge begins to burn and accelerate down the bore. In the meantime the ball is still stationary due to inertia. Very soon the expanding gas sets up a supersonic wave in the bore. The shock wave then slams into the ball and presto, you have a bulged/burst bore. BP burns at about 400 meters per second or in excess of the speed of sound in air. This is not to be confused with detonation defined by the C-J Plane moving through a high explosive.

In theory, the ball can be seated away from the charge a small distance with no ill affect. I'm pretty good with math but not that good so my ball always touches the charge.

Have fun with your new toy.

Bill

[Cat Whisperer]

Pete, DD -

Since DD & I have said nearly opposite things, let me clairify.  The terms explode and detonate in eveyday common useage mean the same thing.  (Look in most of the on-line dictionaries and one is used to explain the other).

However, there is a difference in the technical definition between them; see the explanation: http://en.wikipedia.org/wiki/Detonation .  That is what I was referring to in saying BP does not detonate.  It certainly explodes and is capable of ruining your whole weekend.

There are certain classes of explosive that take a 'detonation' to get them to go; but those are clearly out of the scope of this forum, although I could tell some good stories about deepening farm ponds.

[Terry C.]

What about chambers in mortars?

I see references to shooters using less that the capacity of the powder chamber when shooting at reduced ranges. Does it pose a danger to shoot, for instance, a golfball mortar with the powder chamber only half full (or more to the point, half empty)?

[Cat Whisperer]

What about chambers in mortars?

I see references to shooters using less that the capacity of the powder chamber when shooting at reduced ranges. Does it pose a danger to shoot, for instance, a golfball mortar with the powder chamber only half full (or more to the point, half empty)?

In either cannon or mortar the powder chamber is realatively small.  While I see a real potential problem with not seating the ball close to the bottom, I see a very different situation with the powder chamber being only partly filled.  Others have noted that at least the partly filled chamber makes a consistantly sized air space.  Further, many of us have mortars/cannons with powder chambers and which have a flat base bore - there is air space larger than the powder chamber volume in the space taken up between the ball and the bottom of the bore.

I wish that there were an easy way to measure the pressue (in the powder chamber) with varying amounts of air space.  My personal oppinion (everyone's got one) FWIW is that it doesn't make much difference (powder chamber percentage of fill) and that putting the ball only half way down the bore is a MUCH different case.