10cm M99 shrapnel (technical questions)

Hello guys,

I`m not sure if this is the proper forum for such questions, as it is more firearms-oriented rather than artillery, but i have seen some brilliant minds around that are knowledgeable in both fields and i suppose someone might have an answer.

I just took these photos of my finished 10cm M99 Austro-Hungarian shrapnel shell set (body, diaphragm and fuze).

My questions are the following:

1.) There is a difference in the remaining driving band groove width between the two projectiles (the left one is barely visible while the right one retains more of its original shape). I am assuming this is caused by the fact that, since these are not fixed ammunition, they were fired with different charges (left one with a higher/bigger charge) and the resulting higher pressure caused more deformation in the left band than on the right one. Am i correct in my judgement?

2.) I noticed some faint rifling marks on the centering band. They are present in just one section, approx. 1/4 of the circumference , and are present on just the left shell. I have also seen some in my 8cm shrapnel shell with a similar design (with copper centering band). It is obvious that from a mechanical point of view, they are caused by the shell not being perfectly coaxial with the barrel axis. But how exactly does this happen? Improper shell seating and centering in the chamber area? Barrel wear that causes misalignment mid-barrel?

I would be very interested in your replies!

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The driving band deformation I think is more the question of barrel wear.

The 1/4 circumference rifling marks in the centering band are not from missalining but simply from the fact that the shell by nature is smaller in diameter than the barrel bore. Means a 100% contact is impossible.
And given any projectile and in particular sharapnel shells have a different axial distribution of weight. The projectile by nature has to move to one side (the heavier) inside the barrel and is receiving respective rifling marks. This can be seen on modern day’s artillery too where the paint has rifling marks in the bourrelet area while the diametral side has retained 100% of the paint.

Not the best photo (source. internet) but here a 155mm showing the same effect:
155mm_ICM_experimental_Germany

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Of course a 100% contact is impossible, but i was giving some context.
About the axial distribution, i totally agree with you about the physical aspects, although i would say that this axial deflection is not always the case, or at least not to this much extent. How would you explain the other shell that has no visible rifling on the centering band?

Every shrapnel has extreme shifts in the axial centre of gravity, means they are individual as fingerprints. The other one just had one lead ball inside packed 10mm closer or further to the axis and all went different.

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The deeper rifling marks exhibited by the left projectile indicates a less used barrel with less barrel wear and thus allows for the chance for better contact between the centering band and the rifling resulting in the faint rifling marks.

The rifling on the right projectile not being very deep indicates barrel wear and as such is less likely make good contact with the centering band and less likely to leave marks on the centering band.

Brian

Brian, in theory yes and again depending on the centre of axial gravity.
Though a worn out barrel with an exactly centered shell (accidentally) would also not leave traces on the centering band.

Of course the factors can influence each other.

Brian, i would argue and say that regarding the 10cm above, the right one is less worn out than the left (or at least that they have almost similar barrel wear).

But what about the example with these 8cm shrapnel shells?
It is quite obvious that the left one, with its crisp grooves, came out of a new barrel, while the left one was fired from a very worn barrel. The groove in the middle of the band also exhibits the same behavior as in the 10cm, meaning that in the case of the worn barrel, the grooves in the band are “more filled” then on the new barrel. But that does not make any sense, at least from the deformation principles based on the constant volume law
(new barrel = higher teeth -> more volume displaced in the band -> middle groove filled more ; worn barrel = shorter teeth -> less volume displaced in the band -> middle groove filled less).

Am i being mislead by something?

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I think there may be some more factors than us laymen can overlook.

However EOD’s explanation is straightforward, there is an other thing to consider. These shells might have been fired from three different guns: the M99 field howitzer, and the M8 and M10 mountain howitzers. Although i don’t have information about the number and geometry of their rifling this can also cause difference.
Vince