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stubby killer m4 upgrade


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#1
Technician1

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HELP

This is doing my head in now with the amount we have thrown at the gun

Gearbox has all ultimate parts

spring guide
Cylinder
Piston
Cylinder head
madbull m110 spring

We built the gearbox and added tightbore barrel and one piece hop

Fps around 280 ish

Remove the front of the gun and replace with a tightbore barrel and hop from another m4 that fires at 370 fps, and the fps on the stubby raises to360 fps (long barrel)

This points to an airseal problem around the hop, but all parts are the same apart from barrel lengths

My question is this

How can I upgrade to around the 340 fps on the stubby with such a small barrel.
Do I have to increase spring and bore upthe cylinder

Any answers greatful

Paul

Or

#2
Hibernator

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Assuming the two hop units are also identical, so it can't be different dimensions effecting things I'd say it's the hop rubber in your new barrel. You might not have installed it 100% correctly - it could have gotten moved/pinched when you reassembled the hop. Take the hop unit apart and reinstall, try a different hop rubber if possible.

#3
TPI

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I think it`s only going up because of the length of the inner barrel so yes a spring upgrade is necessary as i think a barrel will only add 2 or maybe 10 FPS per inch depending on how tight it is and try cleaning and lubing it all up and also the gearbox will need Greasing NOT Lubing

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#4
c2ash

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I think it`s only going up because of the length of the inner barrel so yes a spring upgrade is necessary as i think a barrel will only add 2 or maybe 10 FPS per inch depending on how tight it is and try cleaning and lubing it all up and also the gearbox will need Greasing NOT Lubing



its my agm stubby hes on about lol it has a 6.03 barrel in it and a m110 spring fitted i will check the hop rubber and make sure its in right but it is a new one

#5
REMSoft

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The cylinder will need changing if you are using aren't using the stock one designed for that barrel length. Different porting sizes effect FPS with specific barrels.
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#6
c2ash

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The cylinder will need changing if you are using aren't using the stock one designed for that barrel length. Different porting sizes effect FPS with specific barrels.


been done plus cylinder head




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