Speaking of rebated boattails....

[GotRDid]

Well, dug a bit deeper in the stash and found some early 190s, and a box of the 168 “International” match bullets as mentioned earlier. Also have a 168 HPRBT and a 190 HPRBT by Hornady side by side for comparison.
The Winchester and Sierra 190s, while not rebated, differ slightly upon closer examination, but appear to have the longer boat tails than we typically see today outside of the Nosler ABLR.







Winchester on left.

 

[Steveb]

One of the reasons for a rebated boattail is to simulate a flatbase and prevent gas cutting that is common with boattail bullets. Flatbase bullets seal the barrel bullet junction better and the barrels last longer.
This has been known since the 20's when boattails were introduced at Camp Perry.
Another reason is for manufacturing because rebated base punches last a lot longer than full boattail punches and these punches are very expensive.