This thread change was initiated by Winchester at New Haven in response to the problems encountered with oval chambers; this especially in rifles chambered for the WSM cartridges. The culprit was found to be a combination of a poorly fitted thread, the comparatively thin wall of the WSM chambers, and the interupted (broached through)thread on the Model 70 receivers. I had called Winchester about this and told them I was now re-threading to 1 1/16 x16 on any WSM rifles I barreled. I was later told by one of the engineers that they had made a change to the threads on the actions for the WSSM rifles and this change was expected to carry over. I assumed, at the time, that they had simply enlarged the thread to 1 1/16 as I had and was quite surprised to see the 28 TPI threads.
This change certainly makes for a thicker chamber wall and more importantly, the interupted thread is gone. I'm frankly surprised to hear that your friend's rifle had the 1 inch threads. I didn't think FN would have produced any of these.
By the way, I doubt that my conversation with the technical staff member had anything at all to do with the change in thread size. I think the change was already in the works in response to a large number of warranty claims on WSM rifles although most Winchester spokesmen at the time would simply deny there was any problem. GD
