You already mentioned that the 150 gr was the wrong ammo. You were right on that. Not enough velocity. The 110's Barnes works great in the BO and made for it. If you want quiet, Hornady has a sub sonic 300 BO with the flex tip. It is very quiet and it opens up very well. We use the BO and Hornady combo for a local hunting clubs youth day deer hunt. The kids love it, and the ones that shot deer with it has not lost a deer .DRT You also mentioned the 6.5 Grendel in sub-sonic. You would be going down the same path as with the 150 gr. If the bullets are not made specifically for sub sonic expansion, you will be doing the same thing as the 150 gr. If you go with the Grendel, you will need at least a 16" minimum. I wnet down that road back when it was called a 300 Whisper. I had 240 Sierra SMK's at 950 fps. Very quite in my rifle. Would shoot through a 11" pine tree, but was terrible on deer. If a bone was not struck on bullet entry which would allow the bullet to tumble, and tumble it did. If not, it was a 30 cal ***** in one side and out the other. The bullet would tumble if it hit a blade of wheat, because you could hear it tumbling through the field. The BO has a place, and with the right ammo,can be a efficient killer. It came from a special purpose requirement by some elite warriors and it done what it was suppose to do. Match it up right, and a deer does not have a chance. It also is great for smaller stature folks with little recoil, mild report, and as the kids at the club said, "that was awesome".