PDI Japan have taken a liking for the Snow Wolf M24 Sniper Rifle that they actually made a hop-up chamber for it at comes with 2 hop-up adjustable bars for easy adjustments. This is quite a unique take on the hop-up system but they guarantee and even more precise hop-up adjustment that an airsoft sniper would want to have.

It costs JPY4,998 or US$63 at their website but you'll need to ask distributors and resellers for their list price.