Flat loading gates lasted to about 62000 on Ruger's steel framed Single-Six.
It is interesting that WBR would do a flat loading gate on his first SA revolver, but there were probably several factors into why he did it. The first that we think about would be cost savings...since he didn't have investment casting equipment at the time and would have went to the extra expense of having Arwood cast their gates for them, he probably decided that in order to be the most competitive, he should design a more cost efficient gate. Problem is, nobody liked it...which is the reason the Premier Weapons company from California beat him to the punch with their own contoured gate accessory.
Of course, WBR probably didn't like that one bit!!! Somebody else making $ that he wasn't raking in!!!
Another reason that WBR may have done a flat loading gate is that he may have wanted something really distinctive about his revolver so that everybody would be able to associate it as his...especially since much of the Single-Six was just scaled down identically from a Colt, such as the original breech face detail.
Ruger did something later with his original M77 rifle that he evidently wanted something distinctive, to keep it from looking like other makes (i.e. Winchester). He actually had a design patent on the original "flat bolt handle" design...and apparently, nobody liked that either.
Chet15