CONGRATS on the venison!!!
I have one deer and a couple pigs with this exact bullet, caliber and barrel length too! I like the high shoulder shot and was rewarded with a quick kill and no need to track. The hogs where a bit different, but both times thru and thru penetration. That 158FP is a good one too, but at 2100 its approaching top speed in my experience. I love it in my 357 mag Marlin!!
At 1600fps, I am surprised you didn't get a thru and thru. Was the angle that steep? You mentioned bullet fragments in the chest cavity. I have shot a couple deer with the maxi carbine at 2100fps and not gotten complete penetration, but adequate penetration. The last 4 deer shot with the maxi have been DRT. My preference has been the 180 SSP bullet. But for a tougher bullet choose the 180 Speer FP.
Good luck with the rest of the season,
CW