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JoeTheBane

Replacement m100 spring a lot stronger and a longer than current

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hi I ordered a shs m100 spring to downgrade my mp5 to less than 350fps, only to find the current spring is shorter and weaker than the new m100. How would the fps be downgraded with a stronger longer spring? Maybe the spring was mislabeled? I dont have a chrono to test the fps, so i only really want to swap the spring to the right on first time. The current spring put out 355-360fps and I need this lowered by next skirmish.

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just shoot a few thousand BBs through it, it may drop in fps..... or buy some 0.3g BBs, set the hop for them shooting straight and then whack in some 0.2gBBs and see if the fps has dropped below 350, if so then sorted, you'll just be restricted to using 0.3g BBs for a bit till the spring beds in.

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Spring strength isn't determined by length. I have some long springs that shoot sub-300fps and a short one that's in excess of 400fps. It depends more on the strength of the coils and the tension in them. A standard M100 in a short barrel MP5 should shoot at low 300s, unless you have already upgraded all the other bits in the gearbox. It will also change if you have bearing spring guides fitted to the piston head and spring guide base, as that will shorten the amount of space the spring has to fit and expand when under tension on the firing cycle. If you have already stripped the gearbox then fit the new spring and run two or three full hicap mags through the gun to bed in the spring, then get it chrono'd at the next game. And as PT247 said, set up the hop for 0.25s or 0.30s then chrono with 0.2s on this setting, as that should reduce the fps by about 20-30fps. Then play with the heavier BBs until the spring settles in and you can set the hop for your BB weight of choice, although 0.25s really ought to be the minimum weight you use for better accuracy and grouping.

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agreed - length doesn't always mean more

(I keep telling Mrs Duck that one - but she still laughs at my excuses)

 

Sometimes you can feel a strong short spring when closing up box but often that means only a rough rough guide

reason I say that is one time I was fitting a m105 and thought wtf this is a bit beefy....

turns out I grabbed a m115 and wondered why I was shooting 380fps - ahhh the m105 still inits packet

but missing m115 spring enlightened me to one of my many many foolish mistakes

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I couldn't even compress it into the gear box, I'm not weak by any means but it was way too long and strong to compress into it.

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