QuickLOAD calibration -- can you get it to match multiple bullet weights?

[David Bookstaber]

I am analyzing .308 Win loads. Using a single batch of Varget, same primers, same brass, and shooting under the same conditions, QuickLOAD is spot on the chronographed velocity for bullets from 180-220gr. However with 125gr Sierra bullets it's predicting velocity 60fps slower than measured.

Hartmut suggested modifying the Ba of the powder to bring the predicted velocity in line with the actual. But obviously as soon as I do that for the 125gr loads then the predicted velocity for the heavier bullets is too high.

Has anyone found other means of calibrating QuickLOAD? Or are there known "missing factors" in the model that would prevent it from accurately predicting velocities across a range of bullet weights like this?

 

[jdwet1980]

BUMP :

 

[Nomad47]

I like to adjust the weighting factor for different weight bullets. What the weighting factor is supposed to do is compensate for over-bore cases. But when you think about it a 'small-for-caliber' bullet is more over-bore for a case than a 'heavy-for-caliber' bullet.
You can also tweak the bullet weight. Even though it is a 125 grain bullet, you can enter 124 or 123 or even a decimal. This simulates less friction in the bore which would be the case with a bullet with less bearing surface.
And someone on this forum suggested varying "shot start pressure" for different bearing surface lengths in different bullets.
HTH.

 

[Steve Blair]

My experience is that adjusting the Ba is the best way to account for combustion differences. It is reasonable that a given powder would burn differently if contained by a 200 grain vs. a 125 grain bullet. The Ba factor will also vary as pressure increases. I track these variables in my reloading spreadsheet and can then make reasonably accurate predictions of subsequent loads. If you are chronographing at some distance (I use 15'), remember to account for the 6-10 fps correction to muzzle velocity from instrumental velocity.

 

[Nomad47]

Agreed, Steve. I guess I wasn't very clear. I was bringing up alternatives if he didn't want to adjust Ba from his heavier bullet loads.

I even adjust Ba from one primer type to another.

 

[Steve Blair]

Agreed, Steve. I guess I wasn't very clear. I was bringing up alternatives if he didn't want to adjust Ba from his heavier bullet loads.

I even adjust Ba from one primer type to another.

[br]
Yes, that too. Anything that changes combustion may require a Ba alteration.

 

[Nomad47]

Chris Long (the OBT guy) told me he adjusts Ba, weighting factor, and bullet weight until two different charges "track" in velocity. He also said adjusting bullet weight could make up for differences in barrel friction.