GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: TDK on August 22, 2016, 02:11:16 AM
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I just finished up installing a WAR SSG into a Gen2 .25 Marauder. The max FPS I was able to achieve is ~835 with JSB 25.4gr. This works out fine because that's where I wanted to end up, but I want to know if this is typical. I'm also hoping someone can explain the apparent VERY sensitive and VERY small window of adjustment for the spring preload (or what I'm doing wrong).
Definitions first, so we are all on the same page:
gap adjuster - the threaded 'plug' for the end cap that the spring assembly presses against during cocking.
spring preload - the nylock nut on the bolt that compresses the spring
The gap adjuster I bottomed out and backed off 1/4 turn each time I changed the spring preload. I've read 1/4-1/2 turn backed off was the sweet spot. I had no issues, and no need to drop velocity with it, so I just stuck with this.
The rest of the discussion is all about the preload adjustment, as I kept gap at 1/4 turn throughout.
I started with the preload nut flush with the end of the bolt. If I remember right this gave me mid 700s velocity. I then tightened the nut a bunch to try and get into the mid 800s. I had something like 2-3mm of bolt sticking past the nut. Velocity was 500 or less! I thought something was broken. Tightening the nut further kept reducing velocity.
After much trial and error, I ended up with only about 1 mm or so of bolt sticking past the nut, which game me the max of 835 fps. Both tightening and loosening the nut from that point resulted in less velocity. It also became apparent that 1/4 turn resulted in a significant velocity change and I had to do 1/8 turns in order to find the sweet spot.
The gap adjuster essentially 'follows' the preload nut in as you add preload, so that you always get the same spring compression length when cocking the gun, right?. I would expect increasing preload to add velocity up to some point near coil bind, but I don't think I was anywhere near that with my 3mm of preload!
Hoping someone can shed some light on this because something doesn't seem quite right.
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Turning in the nylon nut SHOULD add more preload and SHOULD result in more output. Without having it in front of me to verify, it's really hard to diagnose the exact cause of the problem. But I would suspect hammer drag or some other component dragging on another part. And up until this past weekend, I also thought turning the gap adjuster all the way in and backing off 1/8 to 1/4 turn would result in the best performance. I found out much different while testing.
To get the most out of your MRod, I would suggest getting up with either Motorhead, Travis or Rocker1. They can massage it for great performance.
Here is my testing over the weekend. Skip over to reply #32 for my testing results.
http://www.gatewaytoairguns.org/GTA/index.php?topic=112692.20 (http://www.gatewaytoairguns.org/GTA/index.php?topic=112692.20)
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On my Gen1 .22 with early WAR SSG, the gap adjuster is VERY SENSITIVE! A quarter of a turn would be waaay to much gap on mine. The final gap adjustment was 1/8 of a FLAT on the hex wrench with a total gap of just several thousandths of an inch. Mine is not adjusted for max power though. The spring preload is only about 3 threads in from the bottom of the slotted end. Getting 40 shots w/18gr/avg 805fps-26fpe/25ES per 2500-2600psi fill.
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Ok, I opened it up again to check for hammer drag. It's silky smooth, no problems found.
Put it back together and speeds were right back where they should be. My strings are consistent and the setting is repeatable through disassembly which makes me think it isn't hammer drag.
Using my original tune with 1/4 turn gap as a baseline, I then tried:
gap of 1/2 turn and got change of -60 fps
gap of 1/16 turn (barely backed off) and got a change of +10 fps
Based on this, I'd say the gun likes 1/16-1/4 turn gap. I'm still not sure what is up with the preload, though, and I don't really want to mess with it again and spend more chrony hours chasing that ghost.
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Just a thought. After you change the preload, check your gap adjustment again.
I was told it should be. 020 between hammer and valve stem. You will need to remove
the stock to get measurement
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Just a thought. After you change the preload, check your gap adjustment again.
I was told it should be. 020 between hammer and valve stem. You will need to remove
the stock to get measurement
If you know the thread pitch... such as 20 threads per inch, you can get it really close by just counting turns.
For example, 20 threads per inch would be 1/20th inch per full turn... or 0.050". Half turn would be 0.025", etc.
Not sure what the thread pitch is on the WAR SSG...
Good Luck!