The depth of penetration seems to depend on velocity & boolit weight. Surprisingly to me, boolit diameter does not seem to have much effect. A 200 grain .357 @1,000fps seems to go to about the same depth as a 200 grain .45 at the same speed. Boolit style doesn't seem to mean much either. Round nose or wadcutter seem to be the same. A thin skinned varmint boolit that blows apart easily is the exception to that rule. The ones that break up, seem to then act as several smaller boolits & not go as deep. Somewhere, several pages back in this thread, I posted a bunch of depth data. I'll post a quick general sampling here for convenience. Be aware, that if you shoot small groups (i.e. a lot of boolits hit the same spot) then a tunnel will form in the crumb rubber & the boolits will go much deeper.
Caliber Weight Speed Average Depth
.22LR 30 gr 1300 13.5”
.22LR 40 gr 1150 12”
.22LR 40 gr 1050 10”
.22Mag 40 gr FMJ 1875 14-22”
.22Mag 30 gr HP 2300 10”
.22Mag 30 gr TNT 2200 12”
.223 40-gr V-max 3200 11.5”
.223 55-gr ball 2950 21”
.380 95FMJ 950? 10”
.380 100 LRN 850 10”
.357 130 LRNFP 1300 19”
.357 150LSWC 1250 23”
.357 158 TC 675 11”
.45 200 LSWC 800 14.5
.44Mag 240LSWC 1000 23”
.44Mag 240 FP 1450 30.5”
.44Mag 180-grain FP 1800 30”
.30 cal 150RNFPGC 1300 23”
.30 cal 150RNFPGC 2000 25.5”
.30cal 150 gr Rem PSP 2390 20”