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K25 spring (way) too strong for longshot?

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#1 JoeVC



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Posted 16 October 2016 - 01:34 PM

I just finished modding an old longshot CS-6.  I removed the air restrictor, trigger lock, bolt lock, and clip lock, plugged the leak hole in the breach, and replaced the spring.  For the new spring I used an 11" cut-to-length [k25] spring from McMaster (part #9637K25), since this is what I saw many people recommend on this forum and other places and videos online.


However, after I reassembled the blaster and tried to fire it I immediately noticed that pulling the bolt back is extremely difficult.  I basically have to pull with both hands and support the gun against my chest in order to get the bolt all the way back.


But the bigger problem is that the plunger doesn't lock back.  I pull the bolt back as far as I can (which is within a couple millimeters of as far back as the handle can go) and the plunger just doesn't lock in place as it is supposed to (I hear and feel no click and can feel that the bolt is still under pressure).  I don't for sure know exactly what is happening since I can't see inside the gun, but I am assuming that the spring is so strong that even though the bolt handle is all the way back the plastic inside is bending in such a way that the rear tip doesn't reach the trigger plate.


Both the above problems seem to indicate that my spring is way too powerful.  But I am confused since this exact spring was recommended by almost every post or video I looked at about longshot modding.  For example, in this video coop uses this spring and doesn't seem to be having the same trouble I am in priming it.  I did try removing the new spring and putting the old one back in to make sure I didn't mess something up, but it works just fine with the old spring.


What am I doing wrong?  Am I using the wrong spring?  Did I miss anything?



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#2 CaptainSlug


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Posted 16 October 2016 - 01:56 PM


What am I doing wrong?

Plenty of things. If you upgrade the main spring you also need to upgrade the catch spring.

And the maximum length of the main spring has to be short enough that the plunger can still be pushed back far enough for it to engage the catch. You need to cut off half of a coil, reassemble, and test again. Repeating that process until the plunger will engage the catch.


OR just measure the travel distance of the plunger and determine the length of the space that the primed spring will have to occpuy. Then divide that number by the wire diameter of your spring (.080) and that will give you a ballpark for how many coils the spring has to be cut just short of in order for it to fit when primed.


The back of the plunger tube also needs to be structurally supported much more when you add a stronger spring. The plunger tube when stock is really only being held in place by some stubs that stick out of the sides of it. There's no shelf directly behind the plunger tube to brace it against the shell, so you will have to add one.


coop uses this spring and doesn't seem to be having the same

Most of the guides he makes are full of terrible advice.

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#3 Cartaya



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Posted 16 October 2016 - 04:02 PM

Excellent answer Captian Slug.  And, JoeVC, I would use a [k26] before using a [k25] however, I believe you can fit 5" of a [k26] no problem but if you insist on using a [k25] which will have more precompression and good power. 

This is what Captian Slug is talking about, just simply get all the numbers together and do the math.

2.18 (coils per inch) x.080 =.1744 solid space per inch of spring at full compression x 6" of spring= 1.0464" of solid space,  that should fit fine. 

As for catch springs, I like Century c-528 springs 1"x 7/32" x .028 cut down to 5/8ths with a pair of wire cutters and facing the open end towards the shell.  You can get these at Orchard Supply and Hardware.  However sometimes they are under different numbers we have found, so keep the size of the spring written down not just the model number.


Edited by Cartaya, 16 October 2016 - 04:10 PM.

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#4 The2ndBluesBro



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Posted 16 October 2016 - 04:31 PM

Don't use a [k26], the length you need to use to avoid rattle and provide power all the way to the front has tok many coils for the plunger to go back all the way. For a catch spring, take off one of the clip retention plates from the stock and slip that spring over the stock one. Also, add a sealed breech system like the Artifact hunter kit to get the most out if the power.
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