"If you guys have a serious interest in gunshot wounds you should read Vincent J.M. Di Maio's book 'Gunshot Wounds.'
http://www.amazon.com/gp/product/084...lance&n=283155
In Di Maio's book, Chapter 9 deals with 'Bloody Bodies and Bloody Scenes.'
Di Maio noted that of 185 cases of ******* by .22, only 20% of those bullets exited. Of 60 cases of homicide by .22 only 6.6% exited. These figures are from gunshot heads only. He further adds: "...of the bullets that do not exit the head, the vast majority are retained in the cranial cavity. Thus, internal ricochet is fairly common, occurring in anywhere from 10 to 15% of the cases..." (See page 264 and 265)
Also, you can give Malcolm Dodd's book 'Terminal Ballistics' a read:
http://www.amazon.com/gp/product/084...lance&n=283155
In Dodd's book, Chapter 8 deals with the 'Rimfire .22 Projectile.'
Dodd acknowledges that "...the .22 short and LR rounds also have the reputation of internal ricochet within the cranium, further creating complex injury patterns..." (See page 41)"
There's evidence.