butt-plate, square toe ?

[The other DWS]

When, where, why did the buttplates go from a round toe to the squared off toe with the matching squared bottom surface of the stock itself?

[FALout]

I don't think that there was any progression of that till cartridge arms.  In most cases, I believe that fowlers had that architecture because of the simpler styling.  You might also notice some schools of thought such as southern rifles that would have a rounded BP, but (and I could be way off) most of the northern makers I've studied had squared bottoms other then the military rifles at that time.

[Acer Saccharum]

In general, the longrifle has a squared off toe, and fowlers round. Always exceptions exist.

[The other DWS]

It seems to my limited experience and perspective that the earlier muskets, fowlers, french and english early trade guns, and even the later HBC and derivatives), all had round toed buttplates.  I know very little about the germanic-styled arms; but I've gotten the impression that the flat toed buttplate is almost a definitive characteristic of the ALR.  some how in the evolution from musket/fowler/ (early) indian-trade/germanic guns this squared toe seems to have developed and been widely used.
I'm just trying to figure out why and when.
 I've got half a dozen of the standard reference books on order, but nothing I've received yet seems to clarify this.  I tried searching the archives, but apparently cannot come up with the correct search terms.

  Even the "kit catalogues" that show early english fowler-style buttplates say that if you are wanting to use one to build an "early" or "pre-revolution" rifle you have to clip the toe square.

[FALout]

I think that you would have to look back into the German manufature of rifles for the square-toe aspect.  The Germans were some of the more prolific builders before our nations beginning.  Square toes were fairly common on even earlier German pieces, you can look back a long time before the American uprising to find examples.  Since more rifles were built then fowlers, they likely saw more use also, with that said, the toe plate helped to strengthen the toe of the stock which has always been susceptible to breaking.  Using a toe plate, the squared end of the buttplate transitions the junction.  There are always exemptions as already stated.  I have a book, THE FLINTLOCK FOWLERS by Tom Grinslade with nice examples, but finding substance in the form of why gunmakers did what they did can only be made by educated guess's.   Hope you find what your looking for.