A 17 HMR is a 22 WMR necked down to a 17 caliber bullet. It’s typically 17 grains in weight. It is common to find 20 grain and 25 grain 17 HMR rounds for specific needs. The 17 HMR is a “laser” with flat trajectory. If you like the 17 HMR you might really like the 17 WSM; the most powerful rimfire round in the world. It is a rocket of a projectile and greatly outperforms it’s little brother 17 HMR. But they both have a purpose. It was my pleasure to assist you. RIP Kobe Bryant.

Larry, .17 is the diameter of the bullet. .17 bullets compared to 22 bullet picture here : http://bulletin.accurateshooter.com/2013/01/winchesters-new-3000-fps-17-win-super-mag-rimfire/

Larry, As far as relationship goes .17 caliber is .05 smaller then a .22 caliber round.

.17 HMR is 17 caliber as the projectile is 0.17 inches in diameter.