Why the variance in load data?

[BLR81]

Looking to load some 130 gr SMK HPBT with H4895 in my Browning Blr 81 in 7mm-08. The Sierra Data shows a start of 35.8 gr (2500 fps) with a max of 40.3 gr (2800 fps). The Hodgdon Data shows a start of 39.5 gr (2824 fps) and a max of 42.0 gr (2957 fps).

The Sierra data doesn't get specific about the speed, it just show ranges in 100 fps increments from 2500-2800 fps. But, the 2800 fps for 40.3 gr seems on par with Hodgdon's 2824 fps with 39.5 gr. Hodgdon states the max load pressure with 42 grs is 50,200 CUP, but Sierra doesn't state pressure values. I'm pretty sure the SAMMI Max Average Pressure for the 7mm-08 is 52000 CUP so are the Sierra numbers overly cautious?

So, why are the max loads so far apart, and which one should I go by when loading? Is it safe to load up to Hodgdon's 42 grs or should I stay closer to Sierra's 40 grs.

[GeoffLinder]

Load data varies from different sources. Use midrange starting point from highest data or low start point from highest data. You will be working up to a safe point anyway and not just duplicating a specific recipe without testing anyway, right?

You should always load a series of test rounds in .2 to .4 grain increments and chrono them from low to high while watching for pressure sign when you develop a rifle load, so no big dealio here IMHO.

[klewan]

Between the various manuals, everything is different while they're doing the tests. Primers, brass, what test gun, the pressure measuring device. Then different lots of powder.

It would be just an accident if you got the same results as the manual, you don't know if you're gonna be on the high or low side of their results. So you start low and don't try to blow up your rifle and rearrange your face. Rifles are fun if they are accurate; rarely does the max load give the best accuracy.

[MIAMIbaseballer]

Between the various manuals, everything is different while they're doing the tests. Primers, brass, what test gun, the pressure measuring device. Then different lots of powder.

It would be just an accident if you got the same results as the manual, you don't know if you're gonna be on the high or low side of their results. So you start low and don't try to blow up your rifle and rearrange your face. Rifles are fun if they are accurate; rarely does the max load give the best accuracy.

THIS ^^^^

The max loads in either book should be fine for your gun, but you wanna start in the low-mid range and work up to the best load for your gun and what you want out of it.