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PostPosted: Mon Oct 01, 2018 5:04 pm 
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Joined: Mon Jan 20, 2014 10:32 pm
Posts: 758
Location: Burlington ON
As mentioned in another thread, I put a Vortek kit (full power) in a HW77. It didn't seem quite right and when I took it apart again, for some reason the kit actually stayed in place and didn't pop out. I put a bit of broom handle up it, leaned my weight on it and then it freed itself.
Anyway, when I came to put it back together, I was able to put the cap back on by compressing the spring by hand and without needing my car jack that I normally use on a frame as a spring compressor.
I am therefore wondering if springs take up a compression set and come out shorter once they have been installed a few weeks. Or could there be something wrong with the kit (Vortek have kindly offered to replace it if I find that is the case).
I do not have a chrono but will clock it when I can borrow one, otherwise it seems to be shooting hard enough still.


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PostPosted: Mon Oct 01, 2018 11:58 pm 
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Joined: Sat Jan 25, 2014 9:16 pm
Posts: 1271
Location: United States
Yes, this is normal, to a degree. How much they do it varies on the quality and winding of the spring, and by how much you compress it.
Like a chinese B18 spring takes a set very quickly and by quite a bit, but a spring like the one in my FWB 124 is like new despite being 35+yrs old, having a zillion pellets thru it and leaving cocked for very extended periods.
Imo leaving a gun cocked doesn't hurt it, it simply speeds up whatever set it will take, which imo happens rather quickly anyway. Imo all the crap Crosman claimed about leaving a coil gun cocked was only to boost sales of the new gas spring guns. Now the whole world thinks coils will fail if left compressed. Good thing my car didn't see that propaganda.
If your spring is still straight I'd say it's not defective since defects in material make for a crooked spring sicne each defect bends more than the rest so it points in diff directions. If the heat treat was wrong then I spoze the whole thing could be bad/weak and remain straight. I'd just shoot it and if you're happy with the power then it's good. If not then I'd ask them wth and if that power is normal. If normal then I guess switch back to the oem spring and make a piston liner instead, or use an even stronger spring.


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PostPosted: Tue Oct 02, 2018 11:37 am 
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Joined: Sat Nov 03, 2007 4:19 pm
Posts: 8978
Location: Coalmont BC
Many compression springs, if compressed to "coil bind' (ie all the coils touching) will take a "set" (be a shorter LOA when allowed to rebound)…. This is due to the coils being further apart than they can stand being flexed without "yielding" (bending/twisting in an non-elastic manner)…. Before I install a hammer spring in any PCP, I do this on purpose, so that the spring will not get shorter if I compress it too much on adjusting it.... The spring "rate" doesn't change, but the overall length is less, requiring a different preload adjustment....

Some tuners recommend "setting" a mainspring on a springer by this method before installation, but it may drastically change the preload required to reach a certain velocity.... To set the spring, you place it over a rod, and fully compress it until the coils touch.... This can be very dangerous with the powerful springs in a springer, so much be done using a spring compressor that allows it to be done safely....

If this is not done, and if the spring is being compressed near to the point where it would occur, there is a possibility that the spring will "take a set" and get shorter over time.... This will lower the power of the gun....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
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Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
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PostPosted: Tue Oct 02, 2018 5:09 pm 
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Joined: Mon Jan 20, 2014 10:32 pm
Posts: 758
Location: Burlington ON
Thanks guys, I thought that precisely you two would be able to offer some insight.
Next thing to do is some target shooting and chrono it when I get a chance.


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