KTW 1873 Winchester Spring Upgrade

[No1_sonuk]

Has anyone here upgraded the spring on their KTW 1873 Winchester?
If so, what spring did you use, and what fps did it give?

Mine's running 260 stock on 0.2g BBs.

Several reviews I've read state it's a "standard AEG spring", but it's actually significantly longer than an AEG spring.
Someone else has reported its diameter is in between a VSR-type spring and AEG size.