As Ulvejaeger stated (who is about my age, so remembers stuff like this) the groove around the middle or the original, lathe-turned Nosler Partitions was right around the Partition, and was designed to reduce pressure.
The relief-groove bullets were sold until around 1977. I know this because I started buying and handloading Partitions around then, and within 1-2 years they transitioned to the impact-extrusion (not relief groove) models.
Incidentally, I initially started using 130-grain .270 and 200-grain .30 Partitions in the .270 Winchester and .30-06. Both shot into an inch or a little less for 3-shot groups at 100 yards in the rifles I had then, a Remington 700 and 1903 Springfield, both of which I'd restocked and "bedded" myself. (Oh, and had 4x and 3x scopes.) Which is one reason I've always been a little puzzled by handloaders who claim they can't get Partitions to shoot even reasonably well.
