I’d bet Boomer58 is correct in that the extra 20 grains probably is not issue per se.
If I had to guess I'd say the 20 grains of bullet weight didn't matter but the bullet construction did.
The jackets on the 170 grain bullet were just a few thousandths thicker, and the velocity was lower so the expansion was a bit less, and a bit slower.
I think that’s why the 170s went through and the 150s didn’t.
Between myself and my 2 friends Randy and Brad, we killed 8 deer with 30-30s, and all those hit with the 170 grain bullets had exits including one Randy killed that was hit lengthwise.
Only one of those hit with a 150 had an exit.
Brad was using 170 grain factory Winchesters loads. His deer dropped as well as those hit with my 170 gr handloads using Hornady bullets which Randy and I were using.
I and Randy shot 3 or the 8 deer with 150 grain bullets,
1 Winchester, 1 Remington and one handload with a Speer bullet.
Only the one I shot with the Winchester 150 gr had an exit wound, but it also hit low in the neck in front of the chest so it only had to go about 6” to come out.
Some hunters may have killed a lot more deer than 8 with 30-30s, and they would be better to give advice on bullets than I am.
Also most white tail deer are not as large as Nevada Mule Deer, so that may be a factor too. Just my best guess.