I've got no particular interest in the Keith boolits but have seen this discussion, and sometimes arguments, about what is a true Keith style boolit and whether Lyman or H&G is it.
According to the "history" here:
http://www.hensleygibbs.com/casting/history.jpg
Hensley and Gibbs didn't meet until 1933 and H&G moulds weren't produced until 1941. Just when the H&G #503 came about I don't know.
According to the Ideal Moulds Handbook 1929 the 429421 was available in 1929 (page 90):
https://www.castbulletassoc.org/down...20-%201929.pdf
So, it looks as though the 429421 preceded the H&G #503 by quite a few years. That is if the above info is accurate. That Elmer designed the H&G #503 may also be true making them both original Keith designs. Why would the H&G #503 be different? Improvement from lessons learned or just different for a different mould maker? Who knows?
I know when Dale53 sent me pics of his boolits from his original H&G #503 so I could model the boolit for Miha he was bent on an original Keith design and that was the boolit he wanted. Likely both are in fact original Keith designs and a guy just has to pick what he likes.
The version of the 429421 in the Ideal 1929 handbook appears to have very sharp lube grooves that could be 90 degrees or at least very close.
A mould/boolit I have not ever heard or read anything about is the 429422 right beside the 429421. Makes one wonder why Elmer would design 240 gr. and 235 gr. boolits of near identical design with only 5 grs. difference in weight.
FWIW
Longbow