I just recieved my Classic Army CA90 TR on Friday. It came with a M140 spring. So, it was time to do some downgrading - with the goal to get as close to 380-390 fps. All tests were done with an 8.4 v 100 mAh NiMh battery. Here are my results:
Stock spring (included as a "downgrade spring"): 350-360 fps
Modify S100+ Spring: 340-350 fps
Modify S110+ Spring: 350 fps
ICS M120 Spring: 405 fps (7.6 rounds per second)
Stock spring with an Army Force bearing spring guide: 370-380 fps
So, I'm sticking with the stock spring with the bearing spring guide.
A few questions:
- Why did the Modify S100+ and S110+ springs give essentially the same fps?
- I tried the same Army Force bearing spring guide in my friend's King Arms M4 (with the Modify S110+ spring) and it didn't affect the fps at all. Yet, with my CA90 stock spring, it increased velocity by 20 fps. The CA90 stock spring was an inch shorter than the Modify and had uniform coil spacing. Can anybody shed some light on why the bearing spring guide had an affect on the CA90 but no effect on the KA M4?