Has anyone else had issues using Quickload and the 300 Ultra Mag?

I was range testing load workups today, and can't resolve the velocity over the chrony with the loads and pressures that were predicted. This was especially noticeable with RL50, Retumbo, and US869---in all of these cases the velocities indicated higher than expected while still being as safe pressures. 7828 was the only exception, and it seemed to be close to predictions.

Has anyone else had issues like this? I understand velocity and pressure go hand in hand.....so stopped at an upper velocity.

There was no weighting factor that seemed to help, and my measured case capacity is 117g H2O....

It's a 26" barreled Sako 75, which does have some freebore.....

Don't know if it is a data anomaly tied to the caliber, or if some of those powders are not very well represented by the predictive model.

Quickload has provided excellent predictive data for most of my other rifles and calibers.

Any ideas?

Thanks,

Dan

Dan:
I can't address your RUM but QL is very anemic with predicted velocities out of my .270 WSM. QL is pretty good on predictions of my other rifles so I don't know. At any rate, I load only from manuals & don't depend on QL data for workup.
I too, have wondered about the problem.
Bear in Fairbanks

Interior ballistics is more voodoo than science where pressures and velocities are placed in the mix. In two guns just one serial number apart no given load will produce the same velocity even if the pressures are identical. When using software pressures can be approximated when certain powders in the proper burning speed are selected but whether a velocity can be close to being projected with any accuracy is practically non-existent.
You are not talking about a constant pressure in a smooth bore with a perfectly sealing piston. You are talking about a bullet that varies from lot to lot, a bore that may be slightly larger or smaller than any other bore and the finish on the bore varies even more than the size does. The velocities that you get from your gun at any given pressure level may be higher or lower by hundreds of feet per second than those reached in another gun with the same load.

That is why the manuals have maximum loads. Those loads will be close to the same in a chamber of the same size and shape with the same bullet fit in the bore. No software can predict your velocity any more than the manuals can predict your velocity. Work your way from below maximum up to a maximum load but not beyond it. If you can't find the accuracy or velocity you want with that powder then go to a different powder and try again. You may never get the velocity listed in your gun but if you don't exceed the maximum load you will not harm your gun even over a lifetime of shooting it.

Bear--

Thanks for the info. QL has been a very useful tool, and greatly expanded my understanding of why many of my rifles' behave the way they do....


While I don't have every paper manual, I do have most of them. Companies (partly due to economics) don't shoot every powder--I wish they would list those they shot but DIDN'T get good results from.....

Software doesn't account for all variables by any stretch, but I agree that today's manuals are a good estimate for worst case pressures. Manuals don't even attempt to take your rifle (chamber, barrel, etc) into account. Each truly is a law unto itself.

Cheers,

Dan