Anybody else have this experience with the 17 HM2?

[Ridge Runner]

OK, I really like to hunt squirrels, it was my first hunting experience and I greatly enjoy it. now a little background on the subject. As a kid the only acceptable weapon for squirrel hunting was a shotgun, the guage depended on your level of recoil tolerence, about 1975 I started using a rimfire 22 LR as you all know was "all there is". over the years I took hundreds of the tree rats with a 22 LR, in that time once I shot a very nice mellanistic (black) grey squirrel, in the head. got it to the house and it wasn't dead, totaly incapacitated but not dead, in a vegatative state you might say, would kick and thrash when you touched it.
Since it was a rare black one and I wanted to have it mounted I just let it expire, took a couple hours, thats the only time that happened with a 22 LR.
Last year around christmas I purchased a savage mark II LH in 17 HM2, mounted a 4x16 V series weaver on it with a .25 MOA dot, shoots like a house afirehave shot 5 groundhogs with the lil rifle, one at 148 yds, and 2 date I have killed 18 squirrels with it, now out of those 18, there were 4 all headshot, that were totaly incapacitated but not dead, yesterday shot one broadside through the eye, came out the other eye and he just ran off 40 yds and set down, I dispatched him but can't for the life of me figure out how he survived the initial impact? anybody else seen this? any comments? sorry for the long post
RR