KWA LM4 Piston Cup Mod

KWA LM4 Chamber

The KWA LM4 PTR is an excellent platform for Firearm training or Milsim Airsoft.  With KWA’s Highly efficient Force Velocity gas system and the wide selection of airsoft and firearm accessories compatible with the LM4 system it can easily be adapted to suit your individual needs.  however In any system there is room for improvement, and over the last few years servicing and fielding numerous LM4’s in training and airsoft environments I have discovered many ways to tweak or modify the system to better suit my needs and improve performance.

The latest Modification is something that we have seen KWA implement in many pistols, The AKG, and the GBB Masada.  The Stock main Seal O-ring in the KWA LM4 is a standard round type O-ring and while it does work, this design relies on friction to expand the O-ring during operation and is prone to shrink over time and develop compression loss.  LM4 AKG Piston ComparisonWhile the obvious answer would seem to be “add a bigger O-ring”  In practice this increases the friction inside of the bolt and can prevent the bolt from properly returning to battery.  This often leads to many failure to fire drills, vented gas mags and common OH-NOES faces.  Because of its Cup shape the newer seals will expand while under pressure and then return to its original shape during the forward cycling of the bolt.  This allows for free movement of the bolt within the carrier and a more efficient longer lasting gas seal in your LM4 bolt.  The real challenge here is that the part does not fit in the LM4 and there are no compatible aftermarket kits that include similar parts.  This is where the Modding comes in, Personally I have found that there is nothing you cant accomplish with a dremel and some determination.  With some modification to LM4 Part 60(the inner piston) were were able to successfully fit an AKG part 86(AKG main seal) Resulting in a more gas efficient rifle with crisper snappier blowback.  Lucky for you we filmed the whole thing so you can do it yourself.


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