Projectile Ponderings

[mac_hunter]

Has anyone ever fired a full scale weight solid projectile from a full scale reproduction piece?

Example: 4.5" (12 lbs) solid cast iron ball from a 4.62" (12 lbs) Coehorn or Mountain Howitzer

The question posed is under the pretense that the tube is either machined from solid gun barrel steel or cast from bronze or brass with a seamless steel liner made to exact dimensions of originals used during the war of Northern Agression.

Is this a practice that is not recomended?

If so, why?

[Artilleryman]

Mountain howitzers and coehorns were designed to throw shells not the heavier solid shot.  If you are firing a Napoleon solid shot would be appropriate.  As far as I know gunners who are firing service loads use zinc projectiles (I do).  Zinc has a similar density to iron and melts at around 900 degrees which makes it easy to cast.  I would think that a zinc projectile would not wear on the bore as much as an iron one.

Properly made bronze barrels do not need a liner.

[mac_hunter]

So what would be the maximum weight of a solid projectile that anyone would recomend being fired from a 1:1 scale 12 lbs Coehorn Mortar?

Does anyone have any historical data supporting this issue of what the max weight for a projectile would be from this type of artillary piece?

The tube I will be firing is being lathe turned from solid 1040 round stock steel, made in 1:1 scale.

[GGaskill]

Since the US Coehorn was a 24 pounder, you should give us a drawing of yours so we know what you are talking about.

[mac_hunter]

Sorry about that. The mortar I'm having made is a 1:1 scale replica of a Confederate States 12 pound Coehorn with a projectile tube inside diameter of 4.62" and a powder chamber roughly 2" X 2". Overall outside dimentions will be around 6.5" by 13". I do not have a drawing of it at this time. Hope the dimensions provided will help.

[guardsgunner]

  The proper shell weight for a 12pdr. mortar is 8.34 same as a shell for a 12pdr. howitzer.

[mac_hunter]

Thank you gaurdsgunner. Can you tell me where you got that from?

[guardsgunner]

1862 Ord. Manual  The shell weights are common to all Artillery manuals of the period.  Gibbons "Atrillerist manual " is a good one on the net linked from this site.

[mac_hunter]

Thank you sir.
You have been of great help

[mac_hunter]

Someone please correct me if I'm wrong. As I have gathered from looking over the charts at the end of Gibbon's "Artillerist Manual", 12 pounders (Guns, Howitzers & Mortars) had a bore diameter of 4.62" with a maximum windage of 0.10". Meaning they could safely fire rounds up to, but not larger in diameter then 4.52". The maximum weight of a 4.52" solid cast iron shot would have been 12.30 lbs (used mainly in Guns). The max weight of 4.52" hollow shells filled with explosives would have been 8.34 lbs (used mainly in Howitzers & Mortars). The max weight of 4.52" assembled cannister shot would have been 15 lbs (used mainly in Guns & Howitzers). The max weight of 4.52" assembled grape-shot stands would have been 14.84 lbs (not used during the war of Northern Aggression). So for my modern day lathe turned 1040 steel 12 pound Confederate Coehorn replica mortar, I could safely fire a solid projectile up to 4.52" diameter weighing 8.34 lbs or lighter, however it would not be recomended to fire a projectile weighing any more then that (for safety reasons and to prolong the life of my mortar tube). If anyone objects with my reasoning on this matter I would appreciate hearing from you. If you do object, could you please point me in the direction of supporting data for your objection, like gaurdsgunner was kind enough to do.

[Cat Whisperer]

Weights and considerations are right on the money.

I have a 4.55" bore diameter mortar of 4140 steel (7" OD) powder chamber and bore of about 2.5 calibers.

In it I shoot 4" pvc pipe filled with concrete (about 7.5 lbs) for max range of about 350 meters.  4" pvc pipe is 4.500" in diameter and VERY regular.

Usually I'll use an ounce or three of FFg or Cannon Goex.  I have used FFFg, but do not recommend it (pressure).  The powder chamber and bottom of the bore have rounded inside corners (reducing stress risers).

[mac_hunter]

Thanks CW. I was not planning on using anything less then 1fg for my mortar, once I get it in hand. I have plans to test both cannon grade and 1fg powder, for range out of my mortar once it is finished. Also, the thought had passed my mind about useing pvc or abc in 4.5" diameter filled with concrete as an alternative/substitute for an actual round projectile, cast of iron or zinc.

[Double D]

Yes your assumption is correct that you could fire balls 4.52" diameter weighing 8.34 lbs or lighter. You can also fire balls that are heaver full weight 12 PDR's. 

 It would not be recommended to fire your mortar with projectiles heavier than the hollow shell with regular service charges

You can safely fire your mortar with heavier charges by reducing the charge.  This is a basic reloading theory.  You will see this warning and guidance in Switlik.

The N-SSA sets their guideline to duplicate original loads and shell weights. It gives them a margin of safety on their ranges by controlling what can be shot and their game is to duplicate the period shooting practice.

Gibbons says this:

It is a characteristic of gunpowder, that the greater the opposition offered to the expansion of its gases whilst the powder is burning, the greater becomes the force developed. This fact is taken advantage of in various ways in the science of artillery, Thus, for instance, a, gun is made smaller at the seat of the charge by making use of a chamber, because the powder is thereby more confined, and a greater force developed; and it is found that the form of chamber which delays the escape of the gas the longest, is productive of the greatest force, though for other reasons it is not adopted. In firing shells from mortars, where the angle of elevation is 45°, and the weight of the projectile almost directly opposed to the effort of the powder, we are enabled to reduce the amount of the powder used, on account of the increased force developed. Thus, too, in blasting rocks, the amount of execution by a small charge of powder is apparently out of proportion to its size, on account of the manner in which the powder is confined.

Heavier projectile, greater pressure.  Reduce the powder charge and you can fire the heavier projectile. 

I could not find where Gibbons mention the regular firing of solid shot in a mortar other than for the proof load.  For Gibbons the mortar was a means to  drop explosives upon the enemy.  He had no idea that we might be using the mortar recreationally.

[mac_hunter]

Thanks DD. You gentlemen on this forum have been a great help in educating and assisting those of use less learned and experianced in the field of artillery.

[Double D]

It's simple when you have Gibbons on disk and you can just search words...I really don't know much, I'm just good at looking up!!