Bought a soft version for my TM G17 and a hard version for MWS. Expensive (when compared to Prommy purples) but both provide a noticeable improvement in consistency over the stock bucking.
The Firefly Namako Chamber Packing is a great replacement or upgrade for your standard Tokyo Marui VSR or pistol hop up bucking.
Recommended BB weights
Super Soft - 0.2g
Soft - 0.25g
Hard - 0.28g and above