[rick_in_lb]

I have noticed that there are differant loads for the JHP, XTP and the jacketed bullets. I would not think there would be a differance, is there. I know you can use Jacketed loads in lead but not the other way but can you use the same load for JHP and Jacketed bullets

[P0832177]

In general just because a jacket bullet weighs the same does not mean it behaves the same in terms of pressures from shooting it out of a gun. Different designs have different bearing surfaces, and so this would account for some differences in load data! Plus, then you have to look at the gun or test bbl used to develop the loading data! and, in rifle loads the brass used can affect the loading data too. Say like Hodgdon data with respect to the Sierra 175gr 30 SMK vs the Sierra data for same bullet?

[BluesBear]

You also have to factor in seating depth.
A small difference in seating can have a large effect on pressure.

Many jacketed bullets have a cannelure for crimping.
The location of the cannelure will determine the final seating depth.

[mc223]

There is also the issue of bullet obturation. With the FMJs the rear of some of the bullets is open to the exposed lead core. Upon firing some of these type bullets behave pressure wise, as a hollow base cast with a "skirt" that opens outward with pressure. Not necessarily a bad thing, but may show pressure signs when a same weight HP does not, given both have a similar bearing surface and all other variables are equal.