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Umarex Umarex Zelos hammer spring
- Thread starter nobody1
- Start date
Great information - attempting to tune my zelos for the first time. unaware of the oversprung problem. Have not moved my hamner spring yet but that was my next on my list. Got what I consider very good numbers for 155 bar and 25.5g .217 slugs. 7.03 spread @ 877. One mag only - afraid to try again! First time using nate chrony - didn’t know what I was missing. Anxious for my springs to arrive. Swore off aliexpress but made an exception for the springs. Thanks for sharing.I was successful at getting my Zelos tuned. From the factory, the hammer was definitely over sprung. I ordered several different spring from AliExpress and the one that worked the best is a carbon steel (not SS) spring with 1mm wire diameter, 8mm coil OD, and 70mm length. Link below.
Replacement Hammer Spring
I did need to trim a couple coils off the 70 mm spring and then stretch slightly to the OAL of the OEM spring (65mm). My first attempt with the Reg pressure set to 1800 psi and 19 coils on the new spring turned out to still be over sprung. My second attempt with Reg pressure at 1600 psi worked out much better. The attached EXCEL spreadsheet jpeg snip shows the average velocity for each 1/2 turn in on the hammer spring adjuster starting from flush with the back of the receiver. I got a definite knee in the graph of velocity vs turns-in. I backed the hammer spring adjustment screw back out to be 3 full turns in from flush. This gave me about 910 fps. Accuracy was excellent with a single ragged hole for a 5 shot group.
I also tested my new moderator after getting the rifle tuned. Very happy with the new moderator. Completely eliminated the bark to the point that the loudest sound is now the hammer hitting the poppet valve. The rifle is now very backyard friendly. The moderator did shift my POI 1/4 - 1/3 inch down at 15 yards which is to be expected.
Overall, very happy with the rifle and the tune, All testing was done with JSB Exact Jumbo .22 cal 15.89 gr pellets.
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Tried a 1.0 wire diameter with 8mm diameter to same length as original. New to tuning but thought I had found the knee but at the range speed dropped from 790 to 730! When I took out the spring, it was noticeably shorter. Got some extra springs and will experiment some more but not sure if the spring quality is good enough for long term consistency. May try taking off 5mm from original as one user suggested.
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They may be too stiff for the Zellos but a hammer spring from a Bullshark or P35X might help if you can get somebody to order one for you from SPA (and you are patient, SPA only seems to ship parts with guns and suppliers only get a shipment or two a year). My P35s and my Bullshark have a hammer spring 8.5mm in diameter with 1.2mm wire and 55 mm long. My P35X has a hammer spring that is 8.5mm diameter with 1.3mm wire and the spring is 48 mm long. I'd love to have several P35X springs for my P35s.
The valve diameter has a lot to do with how much hammer spring force is necessary to open the valve. Older P35s and Bullsharks have a plastic 8 mm valve. My bullshark and my P35X had brass poppets that are smaller in diameter (and thus easier to open). I don't know what the Zellos has but in pictures it appears to be brass and looks like my bullsharks and P35X. P35s cannot open the valve with the regulator set at 150 bar or above. If I had both a Zellos and a P35 I would try swapping springs. Might help both guns.
8.5mm springs are rare as I think you are finding. I tried an 8mm spring in my P35-177 and it kind of worked but there is a pin on the hammer spring adjuster that goes up inside the spring and was tight enough the spring bound a little on it. I shortened the stock spring 1 turn and it helped.
The valve diameter has a lot to do with how much hammer spring force is necessary to open the valve. Older P35s and Bullsharks have a plastic 8 mm valve. My bullshark and my P35X had brass poppets that are smaller in diameter (and thus easier to open). I don't know what the Zellos has but in pictures it appears to be brass and looks like my bullsharks and P35X. P35s cannot open the valve with the regulator set at 150 bar or above. If I had both a Zellos and a P35 I would try swapping springs. Might help both guns.
8.5mm springs are rare as I think you are finding. I tried an 8mm spring in my P35-177 and it kind of worked but there is a pin on the hammer spring adjuster that goes up inside the spring and was tight enough the spring bound a little on it. I shortened the stock spring 1 turn and it helped.
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