My very best friend is JD Jones, inventer of the .300 Blackout. He didn't copyright it, so Rem. made the .300 Blackout (same thing). I've had one since it's beginning. I use only subsonic rounds. JD had me test many bullets & hooked me up with Lehigh Defense & tested their bullets. I've taken about 120 deer, 4 turkeys, 200+ groundhogs & a large coyote at 170 yds. All these with subsonic loads.
The Whisper was developed with the Sierra 240 gr. HPBT Match bullet. It killed by tumbling. Worked fair, but I wanted more predictable results. Lesser Sierra HPBT Match bullets did not tumble & gave very poor results. What did work is the Sierra 220 gr. RN. It expands & tumbles).I get 95% instant drops on deer. Killed a heavy 8 point in WV at 240 yds. with this bullet. DRT. Obviously, mildot scopes are required for these subsonic loads that fly like a thrown rock.
For Lehigh, I tested their early bullets. Did not work very well. Then they made a 186 gr. Controlled Fracturing bullet. It has a solid base, a nose with 4 skives that open up & split off the bullet, plus a .17 cal. bullet in the open point of the bullet. You have 6 tracks of bullet damage with this. A "certain govt. agency" uses this. It drops deer Very Fast! (THis bullet also is in .30 & .375 cal. without the .17 bullet. I killed a 220# bear in WV at 220 yds. with the 250 gr. .375 in my .375/.284 handgun. DRT. Base went thru both shoulders. Pedals were in liver, lungs, spine, and backstraps).
I've shot some Horn. subs in my gun (Not killed), & they shoot so far off from my 220 loads That I do not plan on using them. My 220/186 Lehighs work so well I have no intentions on using others. Can't improve much on 95%.
B, I'd highly recommend going quiet. My Whisper sounds like a BB gun. An unaware deer usually flinches at the shot, walks 3-4 yards & drops. Do double shoulder hits. Get a mildot scope & figure out the range of each dot. On my gun at 8X each dot is 25 yds. starting at the top dot.