(A) They added about 1/4" to the inside of the shroud to shorten the fall of the FP, thus requiring the longer firing pins which they made (B). I have at least one Sedgley with the speed ignition feature that has an added loose ring to fill inside the std. Sedgley shroud and I assume this to be an early version.
You can tell if the rifle has the speed feature since the cocking piece will stick out an extra 1/4" when the striker is at the fired position. If it greatly improved the use of the rifle, I have no idea but they were only getting $5 for it.
The other photo shows the Sedgley catalog from 1937 when these features were first listed.
