[Mike / Tx]

Are these already loaded rounds or just dummy rounds for test purposes?

If loaded with the Hodgdon data are they the start load or max load or somewhere in between?

Are you using the top ring as an actual crimp groove or simply seating them up to it for a taper crimp?

To be honest if it were me, and I were only going to use this in a BH, I would simply and seat them in until they just did fit the cylinder length. Then I would check that measurement against the noted measurement in a couple of manuals or listed online lengths as well as the corresponding data.

I would probably then note the start load data for the shortest listed lengths, bearing in mind that this would probably now be within the max load range of my now deeper seated bullet, and back off about two tenths of a grain or so, and use that as a start load.

The thing with the 9mm is that it's a higher pressure caliber and the seating depth usually plays a role in the pressure. It can get squirrely when you seat bullets deaper than they should be with some powders. So if your seating deeper than the listed lenght you need to have some give and take with the powder to compensate for the now diminished area behind the bullet.

That said, #1 your using a lead bullet which will not build pressure nearly as fast as a jacketed," in most cases." #2 your using a light for caliber bullet as well which should also aid in reducing pressure build up to some extent. #3 your running these in a BH and not using them in an auto action pistol which may or may not have a fully supported chamber. That's not to say that you can't blow a cylinder out of a BH, but by going with a slight reduction in charge to allow for the deeper seating depth, and using cast bullets, your chances are slim to none.

This is simply MY take on your situation. I have used this same thought process in the past for finding loads with bullets which I had no data for. It isn't scientific, nor is it guaranteed, but I have never blown anything up being careful to adjust the charge to accommodate the more or less weight, and area the bullet might take up in the cases. Just a few thoughts on how I might go about this if it were me.