My understanding of the theory behind the design of the Rebated Boattail is this. The main advantages to this design over the traditional boattail configuration are and ease understant I am not a ballistics expert, this is just my understanding.
The Rebated Boattail bullets combine the best features of the flat based bullet with the boattail design.
The most consistant and accurate bulets made are flat base bullets simply because it is much easier to make a flat base as perfect as possible compared to a easy sloping boattail.
Now that is not to say modern BT bullets are not extremely consistant and accurate because they are but you only have to look at the 100 and 200 yard BR bullets to see tht they are Flat Base bullet designs.
Te step down if you will is supposed to create a more consistant gas seal and also is supposed to produce a more consistant release from the muzzle at exit as well. This more efficent gas seal is also supposed to increase the throat live of a barrel as well to some degree.
As far as actual ballistic advantage over a traditional boattail, I believe most of the B.C. value is determined by the nose profile of the bullet compared to the boattail.
I am hoping to have the 270 AM up and running by mid Jan.
Wildcat bullets is offering the 169.5 gr ULD right now. You can contact Richard Graves at: firstname.lastname@example.org