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Longer barrel for the CM 030

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Longer barrel for the CM 030

Post by reidc on Sun Aug 29, 2010 7:10 pm

Pictures follow but basically...

I used a dremel cutting wheel (all hail DREMEL) to etch the end of the barrel for the hop up since it clam shells onto the barrel. The new barrel is 363mm long. Just test fired and it looks like I need to widen the etching since the hop up rubber appears to be bunching (I thought it looked like it was). If that does what I think I can cut the barrel down to fit any size silencer I choose. Pic follows...

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Re: Longer barrel for the CM 030

Post by gscoulson on Mon Aug 30, 2010 4:28 pm

reidc wrote:(all hail DREMEL)
You machine lover you... Evil or Very Mad Cool

On the other hand, I'll likely be needing to do the same maneuver on my custom Sterling project I'm working on, so it will be nice to see your pics and results.
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Re: Longer barrel for the CM 030

Post by reidc on Tue Aug 31, 2010 11:46 am


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Re: Longer barrel for the CM 030

Post by Panzerfaust on Tue Aug 31, 2010 12:14 pm

How's it shoot like that?

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Re: Longer barrel for the CM 030

Post by reidc on Tue Aug 31, 2010 12:32 pm

Right now it's got reduced range. When I took it apart I noticed that the notch I ground around the circumference wasn't perfect. I think it's causing the hop up rubber to bunch and catching the BBs. I'm gong to work on that this evening and see what happens.
I must say that having to free hand the notch isn't the simplest thing I've ever done.

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Re: Longer barrel for the CM 030

Post by Panzerfaust on Tue Aug 31, 2010 12:45 pm

The reduction in range may also be caused by the increase in barrel volume, the piston may not be moving enough air to propel the BB all the way out the barrel at speed. Chopping the barrel down should help.

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Re: Longer barrel for the CM 030

Post by reidc on Tue Aug 31, 2010 12:53 pm

I am planning on about an 8" total barrel length. I will cut that down and fix the etching this evening and see how it goes.

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Re: Longer barrel for the CM 030

Post by Panzerfaust on Tue Aug 31, 2010 12:55 pm

Dees wrote:The trick is to try and make the cylinder and barrel air volume match, or to keep the cylinder volume slightly higher then the barrel volume. To make this as simple as possible, if you are using a M4 cylinder in your gun, you have roughly a air volume of 17193.024mm (measured with a digital caliper, accounting for cylinder head penetration and using the equation provided here http://www.mathsteacher.com.au/year9/ch14_measurement/18_cylinder/cylinder.htm)
Now, if you take a stock 363mm/14.25" M4 inner barrel and measure it out (which requires a micrometer, since calipers are not precise enough at that size), you will find a wide range of differences in their inner diameter, but the average is about 6.10mm, so again, to use the same volume equation, you get a result of 10609.929165mm. This indicates a difference of 6583.094835mm, with the cylinder being larger then the barrel volume.
In English, this means that the BB is actually still accellerating as it leaves the barrel, so you have wasted potential velocity and range in this design. You can use a longer barrel with the stock inletted cylinder to provide more range, accuracy and velocity to this gun.
Personal experience with upgrading M4s with TBBs, I have found that upgrading with a 455mm length 6.01mm barrel will give the average M4 another 35-45fps, typically increase range by about 50-75' and cut your groupings more then in half for accuracy, so I would say just buy the barrel and go with it.

I have no idea what the volume of an AEP cylinder is though

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Re: Longer barrel for the CM 030

Post by reidc on Tue Aug 31, 2010 1:23 pm

The easiest way is just to cut it down and see how it does. Since it's a spare barrel I'll never use for anything else I'm not anything even if it doesn't work.

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Re: Longer barrel for the CM 030

Post by reidc on Tue Aug 31, 2010 6:18 pm

Here is the final length. I cut it down to 6.5" since that was the longest barrel upgrade I could find online.
I used a tubing cutter to cut the barrel since I wanted it straight and don't have a band saw.
At first firing it was throwing BBs everywhere. I smoothed out the worst of the inner ridge caused by the tubing cutter and achieved torso sized groupings at 90 ft with fewer wild BBs than with the stock barrel.
I anticipate that jeweler's rouge and approximately 8,000 q-tips will finish off the end of the barrel. Since my yard is only 90' across I will have to wait to dial in the hop up in the field. It looks like I should get torso accuracy at 110-120 feet at this time.
I'll update things if my hopes are dashed. I'll shoot ya on the field if they aren't. Bwuhahahahahah!

http://illiweb.com/fa/pbucket.gif

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Re: Longer barrel for the CM 030

Post by Panzerfaust on Wed Sep 01, 2010 10:37 am

Very nice!

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