Hello Guys,
Many people interested in what power of Three-Nine Ultra Mainspring for RWS 350 is.
http://www.airguns.citymax.com/catalog/item/251488/5130528.htm
I just installed such spring to my 350. Pellet (CP 10.5) speed with new factory spring was 275-280 m/s after 4 years and about 3000 shots the speed was down to 245-250 m/s with JM’s spring speed is exactly the same as with the factory spring – 280 m/s. Just for information speed of Baracuda Match Heavy is 275 m/s. So no dubts guys about power you can go ahead with JM's spring for 350.

It is interesting that Three-Nine Ultra Mainspring has not 39 coils but 37.5 you can see it below bottom spring is JM’s one upper is the used factory spring.

You right 39 coins are true if take into account ends of the spring as a useful coins but them are done more completely than on the original spring so these coins do not work I think. About shooting I did not shot yet I hope next weekend I will do it and report results here. In addition my feeling that cocking is became harder there are no vibration after shot the quality of JM’s spring is better than original.

the quality of the JM kit is way better than oem, the steel is also different and the coils at the end are different for a reason than the original ones, they seat better too

warren

and remember "it's 30% the gun and 70% the shooter"

I'm guessing you installed the JM spring on the factory guide and
kept the factory piston seal in service in your rifle - yes? no?
If so how is the fit to the factory guide? Did you do anything
else - add piston weight, space/load at either end, etc.?

Thanks for letting us know.

Herb

JM’s spring has exactly the same size parameters as original spring has. I did not change other original parts of 360 only replaced old seal by new factory one.