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PostPosted: Tue Dec 22, 2020 6:36 pm 
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Location: Maple Ridge, BC
Hey there everyone, I have a few questions regarding running a sig mcx co2 rifle on hpa. I've had my (detuned for Canadian market) mcx for some time now and other than a few skipped pellets and wildly inconsistent velocities (350 to 580 fps spread lol most shots around 475 fps with 7 grain pellets though(on co2 at 25 degrees Celsius)) it has been a great little plinker.

But I'd like to try and tighten that spread up a little bit and shoot the gun in colder weather. Not to mention get rid of those expensive 90g co2 canisters... So I purchased a 13cc air venturi HPA bottle, 3000psi regulated down to 1100 psi, and an 88-90 gram adapter for the gun.

Now, I wasn't expecting this to be easy peasy, but I was sorta hoping it would be lol... the tank is attached to the gun, all pumped up and its holding air perfectly. However when I chronographed it it was shooting very low, 180 to 300 fps with most of the shots being about 250fps, with a 7 grain pellet.

I'm not looking to make a lot of power because I like this gun as a plinker and it really doesn't have the accuracy for anything else so about 500 fps would be perfect.

Do any of you out there in the know have any ideas about how to fix the low fps? Would a lower output pressure help? Or am I going to have to open the gun and try different hammer or valve springs? ...the gun is very messy inside and I'd prefer to avoid opening it... I've worked on many crosman co2 guns but this is a horse of a different color lol

Any help would be greatly appreciated:)


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PostPosted: Tue Dec 22, 2020 9:00 pm 
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What pressure are you running the bottle? To high and the hammer cant hit the valve hard enough to dump enough air. Also to high causes the valve to close quicker. Try running it between 850-900PSI (pressure of CO2 at room temp)

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PostPosted: Tue Dec 22, 2020 9:15 pm 
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The factory setting using the 88/90g co2, the speed was spreading so widely, was that caused by shooting too fast and the co2 cool down effect?

If so, changing to HPA should make a huge difference ~

I am waiting for mine too... But I don't like to make such a big change and planned on using the 12g co2 convertor...

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PostPosted: Tue Dec 22, 2020 11:11 pm 
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notec wrote:
What pressure are you running the bottle? To high and the hammer cant hit the valve hard enough to dump enough air. Also to high causes the valve to close quicker. Try running it between 850-900PSI (pressure of CO2 at room temp)



Thanks a lot, that was my thought exactly, and the first thing I'll try... the bottle came regulated at 1100 psi, I'll go down to 900 first :)


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PostPosted: Tue Dec 22, 2020 11:16 pm 
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YepYep wrote:
The factory setting using the 88/90g co2, the speed was spreading so widely, was that caused by shooting too fast and the co2 cool down effect?

If so, changing to HPA should make a huge difference ~

I am waiting for mine too... But I don't like to make such a big change and planned on using the 12g co2 convertor...


No, it was not caused by the co2 cool down effect. The gun, even with ample time between shots, is very inconsistent... not a huge issue for plinking. Oddly, it seems to shoot faster while rapidly firing over taking time between shots... an observation I've heard others mention too.

You're going to love your new gun! it's a lot of fun :)


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PostPosted: Wed Dec 23, 2020 12:33 am 
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Sevensson wrote:
You're going to love your new gun! it's a lot of fun :)


Yep, I hope so... I like that I can decorate the quad rail shround... [emoji38] already bought a few tiny add ons for it~

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AA ProSport 177 walnut in 12fpe
FWB300S Universal
HW 30s / 35e / 40+Extender / Scoped P3
HW45 with customized grips from UK
Russian Izzy 46M
2240 14" barrel carbine
Camo Chaser long barrel carbine
PP700SA long barrel carbine


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