I just got back from a full week of fun with Skippy and his pals. As the little ones are out right now, there was a lot of 17HMR action using my Anschutz 1517 and Hornady 17gr V-Max.
Some days I fired over 300 rounds without cleaning, and I was still launching rats past 200 yards with no discernible loss of accuracy. I normally don't go more than 100 rounds without cleaning, but when the sun is shining, rats are running about everywhere, it's hard to stop to properly clean, but before leaving the field, I always give it a 'bare metal' cleaning.
A recent rock chuck outing with "Annie", one of my 17HMR's:
The 17HMR is pretty forgiving in a good barrel. If you clean after every 100 rounds in the rat patch, you should be in good shape. This does NOT apply to something like my 17 Mach IV though or my 17 Ackley Hornet.....that's an entirely different issue altogether.