Barrel Pressures GB Mortar

[Parrott-Cannon]

The attached graphs show pressure and velocity within the barrel of my GB Mortar.  The data was generated by the internal ballistics program I wrote.  The velocities were confirmed by measured muzzle velocities.

[Cat Whisperer]

COOOOOOL.

What were the charges?

Golf balls assumed.

Windage?

[Parrott-Cannon]

COOOOOOL.

What were the charges?

Golf balls assumed.

Windage?

Good questions!
Windage 0.04 inches
Gulfball
The graphs are for 120 grains of each granulation of powder.  The velocity are in barrel.

[Cat Whisperer]

I've been trying golf balls with a damp-wet single-layer patch in a 1.75" bore (very smooth), with great accuracy.  Not sure yet about repeatability, but that will come.  No powder chamber, which puts all the powder on the bottom at the ground side, presumeably giving back-spin.  They seem to be flying very straight at 100 yards and further.  (I'll start a separate thread, with pix.)

That gets to my question.  I wonder what differences there are between windaged and patched golf balls, in pressure, velocity, repeatability in same and accuracy?

[joe-joe]

Interesting.Earlier this summer I ran a golf ball though my chrony.
I used a patched golf ball,300 grains of fffg.I got a real life reading of
970 fps.I only made one shot cause I was afraid of hitting my chrony

[Cat Whisperer]

Interesting.Earlier this summer I ran a golf ball though my chrony.
I used a patched golf ball,300 grains of fffg.I got a real life reading of
970 fps.I only made one shot cause I was afraid of hitting my chrony

joe-joe  WELCOME to the board!

How long a barrel?  Tight, moderate or loose fit on the patch?  Any lube/water?  Smoothness of ID of bore?

Healthy fear of not hitting the Chrony.  A golfball hit would be definative.

FFFg is hot powder.

Range with 300 gr. ?

[Double D]

Okay some questions.

120 grains of what powder?  Different grades have different burn rate and and different pressures.

Is this a mathamatical estimation of pressure or a direct pressure measurement

[Parrott-Cannon]

I've been trying golf balls with a damp-wet single-layer patch in a 1.75" bore (very smooth), with great accuracy.  Not sure yet about repeatability, but that will come.  No powder chamber, which puts all the powder on the bottom at the ground side, presumeably giving back-spin.  They seem to be flying very straight at 100 yards and further.  (I'll start a separate thread, with pix.)

That gets to my question.  I wonder what differences there are between windaged and patched golf balls, in pressure, velocity, repeatability in same and accuracy?

I have found that swabing the barrel and spraying the ball (golf ball) with wd-40 produces a significant reduction in the the muzzle velocity variation - from 23% to 7%.  From what I have been able to find on the "net" 7 % is about what is expwcted for a high powdered rifle.

[Parrott-Cannon]

Okay some questions.

120 grains of what powder?  Different grades have different burn rate and and different pressures.

Is this a mathamatical estimation of pressure or a direct pressure measurement

The graphs show the results for cannon, fg, and ffg powder.  The burn rates are Pressure dependent (25P^0.5 mm/sec) and are the same for all granulations of black powder.  The buen times change because of the size of the black powder particles change with each granulation.  The burn times at 250 psi for:

Cannon grade - 0.0044 sec
fg - 0.0022 sec
ffg - 0.0014 sec

This data is based on a Army report written in 1954 on the physical and thermodynamic properties of black powder.

The muzzle velocities are measured.  The muzzle velocity is the last point in the velocity graph.  The pressures and in barrel velocities are calculated using a modified Nato Lumped Parameter Model for mortars.

[Cat Whisperer]

There will, of course, be variaitons between brands.

There will also be minor variations in measurements  (measuring 10 times will give slight variations between them).

There will be variations between morter 'a' and mortar 'b'; and operator '1' and operator '2'.

BUT, this is a GOOD start in working from real measurements (chrono) and likely good programming.

Of interest, then, is the pressure that is applied to the powder chamber compared to the barrel.

Looking at the distance involved, there is good reason to round the inside corner of both the bottom of the powder chamber (obviously) AND the transition between the barrel ID and the flat that reduces down to the powder chamber.  (To reduce stress risers.)

Next, I am curious about the pressure build rates when comparing different proportions of powder chamber.  (I.e.: thin and long vs. large and short - for comparable volumes.)

[Double D]

Okay some questions.

120 grains of what powder?  Different grades have different burn rate and and different pressures.

Is this a mathamatical estimation of pressure or a direct pressure measurement

The graphs show the results for cannon, fg, and ffg powder.  The burn rates are Pressure dependent (25P^0.5 mm/sec) and are the same for all granulations of black powder.  The buen times change because of the size of the black powder particles change with each granulation.  The burn times at 250 psi for:

Cannon grade - 0.0044 sec
fg - 0.0022 sec
ffg - 0.0014 sec

This data is based on a Army report written in 1954 on the physical and thermodynamic properties of black powder.

The muzzle velocities are measured.  The muzzle velocity is the last point in the velocity graph.  The pressures and in barrel velocities are calculated using a modified Nato Lumped Parameter Model for mortars.

Well duh on me, the graph does say which grades of powder.

[Cat Whisperer]

But yours was a good question, because there are different brands of powder.

[Parrott-Cannon]

There will, of course, be variaitons between brands.

There will also be minor variations in measurements  (measuring 10 times will give slight variations between them).

There will be variations between morter 'a' and mortar 'b'; and operator '1' and operator '2'.

BUT, this is a GOOD start in working from real measurements (chrono) and likely good programming.

Of interest, then, is the pressure that is applied to the powder chamber compared to the barrel.

Looking at the distance involved, there is good reason to round the inside corner of both the bottom of the powder chamber (obviously) AND the transition between the barrel ID and the flat that reduces down to the powder chamber.  (To reduce stress risers.)

Next, I am curious about the pressure build rates when comparing different proportions of powder chamber.  (I.e.: thin and long vs. large and short - for comparable volumes.)

Procedures play a big role in consistency of results.  The shape of the powder chamber as well as the point of ignition in the chamber play a role in efficiency of the charge.  But you can only do so much with a model.  My training is in chemistry, math, and physics - (none in typing or spelling).  Your questions are structural engineering questions that involve stress tolerance of the metal and the impact of shape on the the stress tolerance.  This will require the input from an engineer.

[Parrott-Cannon]

But yours was a good question, because there are different brands of powder.

I have tested powder from both Groex and Schuetzen - and based on velocity produced they are very similar.

[Cat Whisperer]

Most folks serious in single shot blackpowder rifle accuracy know which brand works best in their situation for accuracy.  I'm not at that level.  But I am curious as to the repeatablity differences between each given variable (as between brands of powder).