I used exactly the same load to take two deer last Sunday with my M/S 1910, both with the same shot. I'm not sure how it came about, but I shot once, saw one deer fall and another run off. On examination of the site, I found a blood trail leading away from the downed deer and it led me to the second one, about 50 yards away in heavy undergrowth. A very effective cartridge!

IMR 4320 is too slow burning a powder for a cartridge with a case which is practically straight walled, with just enough shoulder to head space on. I wouldn't be surprised if you found unburned powder granules in the bore after a shooting session.