Vickers Bl 8 inch Howitzer cannon of 1917

Edited By mal webber on 27/05/2022 23:11:36

Edited By mal webber on 27/05/2022 23:13:56

pic is from previous page.

Not directly related but the pictures of obturators reminded me of this accident report:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/727954/20180823-Challenger_SI_Castlemartin_Redacted_RT.pdf

In short a sad story of firing the main gun without the obturator fitted excerbated by poor storage discipline.
Apart from the safety lessons there are interesting details of a modern breech system.

Robert G8RPI

Horrifying.

Hi all, managed to broach out the shape for the plug the last couple of nights, next will be the threads and to see if the breech and plug will fit together, a couple of pics on the plug before I start with the threads.

Thanks, Mal.

Hello all, managed to thread the breech plug last couple nights which all wen't well up up to the point of trying the breech ring on, the breech ring didn't want to go on first couple of attempts so bit of shaping here and there with some needle files and it screwed into place,the plug and breech are in scale with the Howitzer except the o/d of the breech ring which is about 25mm smaller,next is to get the plug to swing into the breech all good practice before I make a steel one which will take a lot longer, couple pics on how it turned out.

Thanks Mal

That's some work, Mal - think your post must have slipped by people in all the festivity..

..fascinating watching this take shape..

Even though I may not post replies but I for one have been following the progress on this build and am amazed at the craftmanship involved. I can only imagine how how the threading was done on this and the time involved in producing it.

Many thanks for the updates as the work progresses

I agree, some amazing work on the project.

Mal

Could you explain to us how you have cut the interrupted threads?

Thanks

Hi Mal are you considering displaying it at the October Midlands show. I know it is not finnished yet but it would be marvellous to see your workmanship.

David

Here is a link that was just offered up on another forum which has a lot of detail on breech block threads. I thought I would add it in here for interest:

https://d.lib.msu.edu/etd/8139/datastream/OBJ/download/Some_engineering_features_of_a_modern_breech_mechanism.pdf

**LINK**

Bump!

From a safety lessons perspective that was a really worthwhile read, particularly the section addressing how the fail-safe design had failed to anticipate an operational practice developed four years later, and the safety reassessment having been predicated on the accident scenario being implausible, based on the correct drills being followed up to that point.

Initially it left me thinking that I'm fortunate to work in an industry which has at this point become extremely thorough in assessing the risk from equipment being operated in unintended states and the potential for a chain of events that lets it happen...

But it further rumination left me thinking "If I was the technical representative on that safety study would I really have spotted the potential for such an unusual operational scenario?".

Which got me thinking about the limitations of the somewhat theoretical approach to HAZOP (HAZard and OPerability) studies often taken, in the context of deciding that a specific equipment condition is or is not plausible enough to consider as part of the study.

For a complex piece of user maintained equipment (like the L30A1), there's a real need for the design authority or safety study leader to ensure a thorough review of ongoing operational practice, empirically and/or via observation of normal users to has validated existing assumptions that rule out consideration of a risk still hold, and that's a potential gap that could easily happen in my sector or elsewhere...

Thankyou.

Edited By Jelly on 12/05/2023 14:13:49

One of the problems with separate shell and propellant is that if the shell is not rammed into the rifling enough and the charge is placed, on elevation the shell can fall back into the breech.

The consequences are dire as personell might still be alongside the gun.

I know of 2 cases, one in the Iraq war when an M109 had this scenario and was lost. Another was an M107 in BAOR.

Measuring rods were made to ensure ramming. Plus Hydraulic ramming fitted to guns.

There was a related issue with the 'Any Elevation' loading system originally fitted to QE class 15" battleships. The idea was to raise the rate of fire by omitting to depress back to level or near between rounds. However, under severe manoeuvreing conditions, as in battle, hydraulic power to the rammers might be starved, and when working at a high 'uphill' angle with a 1938 lb projectile, the wring of the driving band into the rifling leed could fail and the projectile follow the rammer out on withdrawal. The wring could also potentially fail through vibration after the propellant bags had been rammed, which would be much worse still.

I understand that, rather than modifying the equipment, it was decided simply to resume the operating practice of depressing the guns for loading, but to a wider tolerance than before of (IIRC) +5 to +10 degrees or so.