Why is this load data different?

[thefitter]

Got this off the Hodgson site:

250 GR. CAST LRNFP Hodgdon HS-6 .452" 1.600" 9.0 787 7,800 CUP 10.5 946 13,300 CUP


250 GR. HDY XTP Hodgdon HS-6 .452" 1.595" 9.7 743 9,700 CUP 10.8 862 13,500 CUP


Both are 250 grain bullets, both use HS-6 but the powder amounts and pressures are different. Obviously it's the bullet composition that's affecting things but why?

[sequoia_nomad]

A lead bullet is much softer than a copper jacket, and slides down the barrel much easier requiring less pressure.

[pdq_wizzard]

get some reloading books, the ABC's of relaoding is the one I would recomend you start with.

when you are done reading it twice you will know the answer to the ???

[thefitter]

A lead bullet is much softer than a copper jacket, and slides down the barrel much easier requiring less pressure.

Hearing it makes perfect sense but I never would have guessed that, thanks.

[thefitter]

get some reloading books, the ABC's of relaoding is the one I would recomend you start with.

when you are done reading it twice you will know the answer to the ???

I have the Speer manual. I'm waiting for the 9th edition of ABC to come out.

[five.five-six]

looks like the XTP will be seated deeper in the casing leaving less free volume... that can make a big difference in pressure