Shillings with halfpenny collars

[nealeffendi]

The latest issue of Independent Coin News has an article on Mules. In the article Peter Andrews mentions shillings struck in halfpenny collars. Has anyone have any references or knowledge of the subject be it articles or recollections of what dates are involved, how common or rare are they and what are the telltale markers to make spotting the error easier when searching through thousands of shillings or when scanning dealers books or eBay listings.
Have any examples been graded by PCGS or the other graders? Have any auction houses sold any and if so what auction was it.

[gnome61]

There was rumoured to be a 1961 shilling awhile back from memory, but it turns out the example I saw wasn't. There maybe other examples around that are, not sure of any of the other years.

 

[echidna]

1961 is the only one that I have seen.

[nealeffendi]

Looks a bit like a struck out of collar shilling. How do you tell me he difference?

[pra666]

the size perfectly matches a halfpenny and the edge is flat as you'd expect from a collar. Also there appear to be a number of examples. I'll try to take pictures of one for you
in the next few days.

[pra666]

In spite of the edge being flat, I photographed 7 halfpennies and the 1961 shilling in identical conditions, then cropped the images around the coins to give me a size in pixels. The shilling was 746 pixels, the halfpennies 765, 774, 769, 768, 771, 772 and 773 pixels; all measurements +/- 3 pixels.
My shilling is thus is a fraction too small to have been struck by a shilling collar and it is likely that the others are the same. I now believe that Neal is correct, the coin is struck outside collar and has just expanded out to a size very close to that of a halfpenny.

[nealeffendi]

So I see a problem with confirming any example as halfpenny collar if the possibility exists for a struck out of collar well centred shilling could expand to the same diameter as a halfpenny. Although I guess if a whole bunch of out of collar shillings (centred or uncentred) are measured and none approach the dimensions of a halfpenny then it would be reasonable to presume that any that turn up as the correct diameter are true wrong collar. But if uncentred out of collar shillings are found with the same diameter as a halfpenny then it becomes impossible to confirm any possible wrong collar shilling from a centred out of collar shilling.
Are there any marks that a halfpenny die collar makes that would make wrong collar shillings identifiable?

[Mister T]

Are the halfpenny collars shorter i.e. less high than shilling collars?

[Tanecoins]

What I find strange is that a halfpenny is 25.4mm and shilling is 23.5mm meaning the former is 2mm larger yet both coins weight the same 5.66 grams. Bronze must be light than Silver and Copper.

Halfpenny collars are skinnier than shilling ones and the other big difference is halfpenny rims are plain, whilst a shilling's is reeded. So the coin shown is definitely a half penny collar due to its plain edge and therefore its likely this coin weighs more than 5.66 grams.