Replied to your PM.

Short version of that is use the mid point data of the FMJ data or data for a cast lead of the same weight.

In the 38 Special when I used Berrys bullets I loaded them almost to FMJ data as they are not going to go over 1200 fps. Don't roll crimp them to hard or you will break through the plating. Crimp a fw dummy rounds and then pull the bullet and you will see and indent. Or as i mentioned buy a taper crimp die.

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Still Running Against the Wind

Alliant has the data for 125g plated right on their website.

Yes, Gold Dot bullets (GDHP) are plated (very thickly electroplated), not jacketed. In any case, just remember that Alliant load data is max load so you should start with a lower charge like 4g and work up to where you find best accuracy.