i used them all the time in my hw90k when i had her (*sobs at memories) i never washed anything and the gun was bang on accurate for years and i put a lot of them through it tens of thousands over the time i had it. bloody great gun should never of sold it i was a fool, a fool i tell thee but anyway i dont think its nessasary at all well i didnt find it to be for me. ive been told you shouldnt clean airgun barrels too cant remember who and why they told me but i do remember it