AirsoftPro show the upgrade set for the SNow Wolf Kar98k airsoft rifle that does not require any modding just to install.... "Upgrade set for Snow Wolf Kar98k bolt action sniper rifles. The package include five basic parts to increase performance. Does not require any gun modification.
Aluminum piston:

• Unlike the original plastic, it is made of strong and light aluminum.
• Provides greater durability.
• Six air channels improove sealing.
• The optimal diameter of the sealing o-ring ensures a very good seal and thus a high and stable performance.
• Length: 79mm, outer diameter: 19.8mm, inner diameter: 12mm
• Weight: 19g
• Spring guide:

Made by precision machining of stainless steel.

Suitable for original SW and upgrade AirsofPro springs."