A question: 17Pdr APDS

[Listy]

This is more of a history thing, than a physical round question.

As we all know early 17Lbr APDS was pretty inaccurate. And during the last two years of the war (and beyond) several experiments were carried out to improve its accuracy. I've been flicking around and finding lots of odd sources, but none paint a clear picture (and annoyingly the Ordnance board Proceeding that says "17Pdr DS shot accuracy trials" was omitted from the book. Lucilly I was after something else, and had a passing interest, hence why I looked.

So as I understand it the 17Pdr APDS evolution goes something like this:

MKI: Bog standard APDS round, with the woeful accuracy.
MKII: The Centre of gravity was moved slightly back, which improved the accuracy, and there may have been some minor Canadian additions to the design. This started coming into service towards the end of 1944.
MKIII: Post war round, using the Canadian Pot Sabot type.

So how close am I? Or is there a better summary?
Thanks.

 

[Przezdzieblo]

Are you sure about marks? Data I saw mention something like 17 pr APDS Mk 1 (Permutter design), 17 pr CND Mk 1 and Mk 2 (Caddy) or so. Looks like Canadian design, at last in mid 50`s, was given own mark numbers.

However, I did not read in deep enough to give conclusive answers.

 

[SG500]

Some photos, hope they help. I don't know if the 1944 dated one is Mk 1 or Mk 2 because its not stamped on it.
All INERT.
Dave.

Mk 1 or 2 to the left dated 1944, mk 3 centre dated 1952, Canadian design right dated 1948


Stamping on sabots. Mk 1 or 2 to left, mk 3 second from left, Canadian design right



Comparison of Mk 1 or 2 and Mk 3. The base on the Mk 3 is thicker shown to right


Comparison of projectiles. The mk 3 to the right is significantly lighter than the one to the left. Tracer to Mk 3 is longer. Last photo shows all 3 with Canadian design on right

Comparison of Sabots

Canadian design shown next to Mk 1 20 pounder

 

[Przezdzieblo]

Very nice pics.

Just a drawing from Feb 1942, called "Service Shot, AP, DS, QF, 17 PDR". No Mark mentioned - but could be compared with pictures.

 

[Przezdzieblo]

Sorry for a bit of topic hijacking.

SG500,
I found a drawing of 20 pr APDS, which looks very like that one from your collection, I attach 'upgraded' scheme. Design changed from 17 pr, not only new shape of subprojectile, but also material of sabot pot (I guess, duralimin, instead of steel) and new locking device (plastic disc called 'locking cup', instead of 'horseshoe' copper clip). And here is my question - what is locking device on your 20 pr APDS: plastic disc, ring, spider?


Btw. How long it is possible to edit post before that option is disabled?

 

[SG500]

SG500,
I found a drawing of 20 pr APDS, which looks very like that one from your collection, I attach 'upgraded' scheme. Design changed from 17 pr, not only new shape of subprojectile, but also material of sabot pot (I guess, duralimin, instead of steel) and new locking device (plastic disc called 'locking cup', instead of 'horseshoe' copper clip). And here is my question - what is locking device on your 20 pr APDS: plastic disc, ring, spider?

Hi, some more photographs

17 pounder base to left, 20 pounder base to right


20 pounder locking device - steel tracer that screws over the base of the sub projectile.



17 Pounder locking device - steel tracer that screws into the base of the sub projectile


17 pounder locking device on left, 20 pounder locking device on right in all photos

 

[Przezdzieblo]

Awesome!
What I see, in both cases there is black plastic ring that fit into a rim (17 pr) or a step (20 pr) of tracer, and this is supposed to be element that lock subprojectile to the sabot. Tracer remains with subprojetile until external ballistics turns into terminal ballistics. In case of early 17 pr, as mentioned, it was a copper horseshoe, that melted during firing. Plastic ring would just shatter/evaporate.