[6pt-Sika]

About what time did the lifter guns change from the 90 degree breech face to water table to the rounded inner corner that went on into the later guns ?

I've been told the older guns with the 90 degree sharp corner had a tendency to crack there dunno if that's true or not . But was curiouse when they went from the sharp 90 degree to the shall we say rounded inner corner .

I am sure theres a more technical way to say that but I don't know it .