The other large factor is what unit was used to develop the load. Test barrels very a LOT from source to source and many companies do not load to the full SAAMI/CIP max pressure. Some may stop at 55K vs. going to the full 60K. By and large the difference between bullets is (as stated above) Bearing surface, jacket material/thickness (i.e. friction coefficient), and core construction. Mostly in that order from largest difference to smallest, that is that bearing surface has more to do with bullet A to B than jacket than core, except in the case of a solid where the later two are the same and it is all based on total contact area ala' bearing surface. There are a lot of other little things that get thrown in to the calculation but they are more minor details that will be overshadowed by those above.
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