I just loaded and shot some 129 Hornady IB's over Re-33 in my 264 WM, and, when I got home, I compared the actual chrono'd velocities to QL. To get an exact MV match, I had to lower the weighting factor to .39 (the QL instructions say an overbore bottleneck case would have a .33 default value).

Has anybody else adjusted QL for the 264WM?

I don't understand why the weighting factors are not fixed as a part of the database for each cartridge...but they just aren't. I think that each cartridge will have a unique value for that field, and there's no way I can think of to determine what the real weighting factor should be. I do realize that if you lower the value, the program shows greater latitude in terms of charge weight. Whether or not the weighting factor should be .33, or .39, or whatever, anyone's guess is as good as another. I think the burn rate adjustment for the particular lot of powder you're using might be just as much a factor in matching up your QL solution and real results.

I found one thread at another site where one guy did the following calculation to categorize how "overbore" a cartridge was.

Case capacity (grains in water) divided by Bore Area (pi times Bore Radius-squared).

So, when I apply that to the 264WM, I get a quotient = 1,526. When I tried it on a 30-378 Wby, I get a quotient = 1,693.

Then, he compared his overbore ranking to what QL listed as the default weighting factor that appears in QL for that particular cartridge. For the 264WM, I got = .50; for the 30-378 Wby, I got .52.

His overall conclusion seemed to be that he didn't feel like QL's default weighting factor always took the "overbore-ness" into consideration.

Interesting. YMMV