Maple Leaf Super Hop Up Rubber 75° for VSR-10 & GBB

The Maple Leaf Super Hop Up Rubber 75° for VSR-10 & GBB is specially developed for use in the VSR-10 sniper rifle or GBB Airsoft replicas.

The number of degrees says something about the hardness of the rubber. 50 Degrees is the softest variant and 80 degrees the hardest variant. The different hardnesses can be applied in different ways in your replica.
Indeed, it makes no sense to use the hardest bucking when it is around freezing point because the cold makes a bucking stiffer and thus harder to adjust. Especially in cold temperatures, you want a softer bucking.

Also, the hardness of the bucking is also linked to the weight of the bb you are playing with. You can easily use a 0.30gr bb on a 50 degree bucking, but this will probably result in it needing to be replaced faster than when you use this weight on, say, a 70 degree bucking.

Ultimately, then, it comes down to personal preference.