Bo Rich said
I recently examined a Model 75 Sporting rifle.  It featured a grooved receiver top.  Along with the rubber style Winchester marked grip cap.  Collecting Model 70s I know that the steel type grip cap on the Super Grade replaced the earlier rubber Winchester marked style in 1955.  Would the Model 75 have the same change in 1955?  

  

Bo,  My understanding of the way Winchester made such changes is this: 

1. As inventories of the old style got low and an order for further production (or an order to an outside contractor) would otherwise have been placed, an engineering change order would stop it and production of the new style would begin. 

Or, sometimes, if there was a large enough inventory of “new style” parts — originally intended for a slow selling or obsolete model, the change order would direct use of those.

[Higher Authority needed my attention and I hit “send” inadvertently]

As a consequence, for a time — sometimes years — the old and new style parts would be used for current production until the old style was used up. 

My point is, the exact date of a change order [records in Cody] is not a hard stop in use of the older style part, particularly as it pertains to cosmetic parts

For example, from Houze we learn the first grip caps for the Model 52 Sporting were steel caps originally designated for several styles of the Model 21 shotgun. However, there are specimens of late production Model 52B Sporting rifles also wearing the same steel cap – and yet other 52B Sportings with even later serial numbers that still wear hard rubber caps. 

Given Winchester’s obsession with never throwing away a usable part – ar least until McNamara’s Band took over — it is nearly impossible to judge authenticity based on old vs new style parts, particularly cosmetic parts.

My answer to your exact question is an uneducated probably.

JWA has written a definitive book on the Model 75 that has gone to press and will soon be available. If anyone has a copy of the change order from the Model 75 production file, it would be Jeff. He would also be the expert to ask.