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Dr. Frankenstein

Low FPS issue.

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My issue is low FPS on a new unfielded ICS CXP M4, Normal FPS was supposed to be 360-390. But here is what I did, I turned the CXP into an SPR and added a madbull 509mm 6.01 tbb, and thats it for now. I took it to the shop to chrono and then field test, 298 FPS and a 72 pace range which translates to roughly 150ft. Im hoping someone has some insight into why the FPS is so low and what I can do to fix it.



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how long was the original inner barrel length? it could be that there isn't enough air in the cylinder to get the BB all the way out the barrel under pressure.

what happens is, the BB gets like 3/4 of the way down the barrel but runs out of air pushing it forward. it starts to create a vacuum behind it because theres no air in the gap behind the BB that keeps expanding as the BB makes out that last 1/4 section. Its like the same idea as dipping a straw in a drink and holding your finger on the end of the straw to trap the liquid from falling out as you raise the straw from the glass.

The solution is to put the old barrel back in or get a bore-up/unported cylinder. its also possible that you messed up the install and you have an air leak.

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No doubt then your original cylinder is probably ported to only have enough air for that short barrel. you want a cylinder with no port for sure and almost 100% sure you want a bore up cylinder. That means you need a bore up cylinder head and piston head too btw.

I'm fairly sure that they do. you might want to look for ICS brand parts. their stock and aftermarket parts aren't bad at all and sure to fit into their own model.




Edited by Hellion_Blade

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