Here is the flash hider that I got for my 15-22 after seeing it on a You Tube video it is made for the 10-22 but fits the 15-22 it just slides on and has a set screw on the bottom in the video it looked very good I cant speak first hand on it as my S&W is back at Smith to fix the blown up extractor however I did order and receive the flash hider and it looks well made. Here is the link to ebay where I purchased it.
RUGER 10-22 BLUE MUZZLE BRAKE SHORT STYLE - *BEST BUY! - eBay (item 200397908351 end time Nov-22-09 17:45:17 PST)
Does this require any alteration to fit on the 15-22? I saw a post earlier where someone said they had to use the dremel to get it to fit.