.17 does mushroom fast.. Hornady seems to break up fast, not really mushroom. CCI hollow points have better penatration. Varmint Al has some 17. HMR tests on his website. Most of the results I expected. The only
one that really suprized me was the results of the lead tests he did. You can check it out for youselves. He seems to
have done a very good job with ballistics, grouping and the type of damage the various .17 loads can do.
http://www.varmintal.com/17hmr.htm