What I have found is that subsonic 147 gn bullets give less felt recoil in the DB9. While I keep hot Underwood Xtreme Defender rounds for carrying, I practice with these.
https://www.midwayusa.com/product/1021034161?pid=473987
I made a couple of 3" J frames for plain clothes guys who wanted the power an extra inch would give them. I don't know why S&W didn't offer them back in the day.
2% is the usual amount needed to have bullets fill out the mold and anymore is really wasted. The third part of the alloy that you need is Antimony. While tin hardens lead somewhat, most of the hardness comes from Antimony. A good alloy for pistol bullets is 95.5% lead, 2.5% antimony and 2%...
E, where did you get that holster? I have the same one that I got from a Chicago cop who used to make them on the side. I think I got it in the late eighties or early nineties.