10 inch mortar ellipitical vs trapzoidal powder chambers on range

[Parrott-Cannon]

[Artilleryman]

If I read this right, elliptical is more efficient out to about 1 mile.

[Cat Whisperer]

One mortar with two chambers or two right-much similar mortars?

Eight different charges.  One shot per round or several shots averaged?

[Parrott-Cannon]

One mortar with two chambers or two right-much similar mortars?

Eight different charges.  One shot per round or several shots averaged?

Good questions.Two mortars were use with different chamber configurations.  The report pointed out that the elliptical chamber shape increased the bore length by three inches.  Five shots were made from each mortar at each powder charge the range reported was an average.  Unfortunately the individual data for each shot was not reported.  The shape of the curves my be more important than the difference.  It appears that the elliptical shape causes a more efficient burning of the BP, while at lower load densities the trapezoidal chamber shape is less efficient.  I have been trying to model mortar internal ballistics for over two years and have found a similar pattern at full load density the model works but as the load density decreases the model over predicts the muzzle velocity.  A cylindrical chamber shape that is used in many of the reproduction Coehorn mortars produces an convex velocity versus powder charge curve.  Velocity and range are closely related

[Cat Whisperer]

One could argue that the 3" difference in bore length was the cause of the differences and not the shape of the chamber.

[shred]

One could argue that the 3" difference in bore length was the cause of the differences and not the shape of the chamber.

I believe that was mentioned in the original article; something along the lines of "slightly longer barrels may be preferable", but no followup was provided.  Looking at the next generation of seacoast mortars however, the barrels are mostly longer.

[Parrott-Cannon]

One could argue that the 3" difference in bore length was the cause of the differences and not the shape of the chamber.

You make a good point but it does not explain the concave shape of load versus range for the trapzoidal chamber.
 

[Cat Whisperer]

One could argue that the 3" difference in bore length was the cause of the differences and not the shape of the chamber.

You make a good point but it does not explain the concave shape of load versus range for the trapzoidal chamber.

I think a valid comparison would be comparing two identical mortars (except for chamber) - identical in length and diameter.

But I think it's commonly accepted, all other things being equal, that for a given charge a longer barel will give a greater velocity.

[Parrott-Cannon]

One could argue that the 3" difference in bore length was the cause of the differences and not the shape of the chamber.

You make a good point but it does not explain the concave shape of load versus range for the trapzoidal chamber.

Barrel length has a impact on velocity.  But it by itself does not explain the data.  The graph below is for the relative difference between the two mortars.  If velocity dur to barrel length were the controling factor the graph would be a near linear function.
 


I think a valid comparison would be comparing two identical mortars (except for chamber) - identical in length and diameter.

But I think it's commonly accepted, all other things being equal, that for a given charge a longer barel will give a greater velocity.

[Cat Whisperer]

I would prefer to see contolling one variable (length) and comparing effects of the other variable (chamber form).  One might get away with deriving the effects of length emperically by changing the length and plotting the results for each.  Generally not practical.

What could be done is to have ONE mortar with 'drop in' chambers - that would allow several forms to be tested AND control a lot of the variables.

DD and I both developed very similar styles of what he called the KISS style of mortar when we did the "we'll send you a few pieces of steel and a chunk of oak if you send us the postage" contest.

With those it is easy to change the chamber by making a replacement AND at the same time cut different lengths of tube.  I still have a few pieces of the 1144SP that I could provide if anyone wanted to persue this project in golf-ball caliber.

[Parrott-Cannon]

I would prefer to see contolling one variable (length) and comparing effects of the other variable (chamber form).  One might get away with deriving the effects of length emperically by changing the length and plotting the results for each.  Generally not practical.

What could be done is to have ONE mortar with 'drop in' chambers - that would allow several forms to be tested AND control a lot of the variables.

DD and I both developed very similar styles of what he called the KISS style of mortar when we did the "we'll send you a few pieces of steel and a chunk of oak if you send us the postage" contest.

With those it is easy to change the chamber by making a replacement AND at the same time cut different lengths of tube.  I still have a few pieces of the 1144SP that I could provide if anyone wanted to persue this project in golf-ball caliber.

I always prefer the experimental approach but I do not have the equipment to do the experiment you propose but I do agree your approach is a good one.  I would use ball of different weight because the mass if the ball also impacts the muzzle velocity.

[seacoastartillery]

I would prefer to see contolling one variable (length) and comparing effects of the other variable (chamber form). 

What could be done is to have ONE mortar with 'drop in' chambers - that would allow several forms to be tested AND control a lot of the variables.


 it is easy to change the chamber by making a replacement AND at the same time cut different lengths of tube.  I still have a few pieces of the 1144SP that I could provide if anyone wanted to persue this project in golf-ball caliber.     

     When I read these lines, I asked myself, "Where have I read about these ideas before?"  Vite! Vite!  Quickly I checked the recent months of entries in the voluminous GBO Mortar and Cannon thread archives.  Voila!  The thread, she is here: 

                                                         http://www.gboreloaded.com/forums/index.php/topic,259781.0.html

     Check out the third paragraph, is this not the same as that suggested by the second highlighted portion of a line in RED above?
Bravo!  Actually, the more experimenters the merrier it will be.  It would be fun to compare notes, etc.  If no one wants to take it up, Mike and I will be pursuing this as soon as we get back from our cross country Brooke delivery trip in late September.

Tracy