The heavier weight is from the alloy, more lead less tin/antimony. You’re right in the wheel house with your loads. I’ve gone to 13.0 2400 with that bullet and no problems in my guns. You didn’t say what gun. If it’s an N frame Smith you may have to crimp over the driving band to get them to fit. The softer bullet from Matt’s can cause some leading if driven too fast.

Dan