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FPS isn't stable


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#1 kwaispro727

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Posted 04 May 2013 - 02:44 PM

My FPS isn't at all stable, for a gas gun I mean.  My M9 stays between 326 and 332.  But my MP7 is all over the place all of the sudden.  I went outside to shoot a magazine or two before I take it down to put in my new barrel when it gets here.  As I was shooting I noticed that sometimes the BB dropped significantly.  So I took it inside and chronoed it.  At first it was consistent around 398-417.  But it kept dropping down to about 300 randomly.  So I decided to take all of my magazines, fill them about half way with gas, and I put 10 rounds in each.  So I went through them all, with the same results.  One of the five gave me a particularly low fps, most of the shots were in the 300s.  Another shot almost completely in the 400 range and the first few shots were about 430-440.  The other three were sort of in the middle of the two.  What could be the problem?  A bad seal somewhere?  Is something not lubricated enough?  I've been trying to be careful not to get the bucking swollen because that happened to me a few months ago.

#2 gcw360

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Posted 04 May 2013 - 09:24 PM

How are you maintaining the gun?  Have you lubricated the piston?  How often do you lube the gun?  Can you post pictures of the bolt assembly?

#3 kwaispro727

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Posted 05 May 2013 - 05:13 AM

I haven't been shooting it much, so to be honest I haven't really done much with it.Posted ImagePosted ImagePosted Image

#4 gcw360

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Posted 05 May 2013 - 07:46 AM

When you pull back on the cylinder does it spring back smoothly?

#5 kwaispro727

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Posted 05 May 2013 - 10:08 AM

The cylinder is...?  Sorry haha I don't know what part that is.

#6 gcw360

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Posted 05 May 2013 - 10:35 AM

It's the polymer tube, in your second picture, that accepts the gas.  The nozzle is on the front end.

#7 kwaispro727

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Posted 05 May 2013 - 10:37 AM

It sticks a tiny bit but it seems to move freely enough.

#8 gcw360

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Posted 05 May 2013 - 10:47 AM

View Postkwaispro727, on 05 May 2013 - 10:37 AM, said:

It sticks a tiny bit but it seems to move freely enough.
Ok, slide the cylinder forward to reveal the cylinder head, put a drop of silicon on the cylinder head and where the cylinder slides inside the bolt, work in the oil, and test the gun.  The idea is that the cylinder should travel freely.  Report back the results.

#9 kwaispro727

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Posted 05 May 2013 - 11:43 AM

Putting the silicon on the cylinder head seems to have helped a little bit.  Most of the shots remain in the 400 range.  Except for one magazine.  Most of them are closer to 300.

#10 gcw360

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Posted 05 May 2013 - 01:10 PM

View Postkwaispro727, on 05 May 2013 - 11:43 AM, said:

Putting the silicon on the cylinder head seems to have helped a little bit.  Most of the shots remain in the 400 range.  Except for one magazine.  Most of them are closer to 300.
Then that mag's release valve is probably sticking.  I would empty the gas out and put a drop of silicone into the valve, work it in, and retest.

#11 kwaispro727

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Posted 05 May 2013 - 04:54 PM

That seems to have done the trick.  Thank you.

#12 gcw360

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Posted 05 May 2013 - 05:52 PM

View Postkwaispro727, on 05 May 2013 - 04:54 PM, said:

That seems to have done the trick.  Thank you.
Awesome.  Glad you are all good :gun: .




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