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Rebuilt my APS CAM870 and did some mods!


Full length front end with 7+1 capacity, vertical pistol grip pump forend and pistol grip at the back.


Drilled two holes in the receiver to mount a rail piece to hold my optics, and at same time modded shell catcher to fit.


APS optics rail kit that goes around the top of the receiver prevented me from putting the shell catcher on. I want both for when I play games with this bad boy :D


Looks and feels pretty awesome!



Nice, when I saw that I thought of this.




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With a few exceptions, this is the business plan of almost all the entire airsoft industry.

Awww yeah.  Super Shorty version incoming  

FPR steel bolt, looks much more realistic than the original, cycles the same as before.   

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Got mine all done up, got to try it in-game, and did some work on making homemade wads and varying payloads- all in all a productive week. First, here's the gun:





I'm very happy with it so far, but buying the APS wads and paper seemed like a total ripoff so I decided to make my own. After a few failures I found two methods that seem to work really well, one for CQB using a shot card, and the other for longer range using a homemade shot cup.


I wrote up a guide and put it on Imgur. Hope you guys find it useful. Here's a pic of the finished product:



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I did a little bit of experimenting today. One of my shells was experiencing a lot of friction between the valve stem and the channel it rides in, which was making it hard to trigger. Following the advice of a user on the Airsoft Canada forums, I drilled out the channel with a 1/4" drill bit:




This immediately produced a number of improvements:

-The friction in the channel is gone and the valve slides smoothly.

-The charger knob (the part you screw to lock in the shell) doesn't stick to the shell, which makes it easier to charge the shells.

-The shell expels less gas when it 'sets' itself while unscrewing the charger knob. Where before it was a bang, now it's just a quick hiss. This means more gas in the shell, and less wasted.

-The shells extract more smoothly from the gun, since the channel doesn't 'stick' on the firing pin as much.

-According to the user on Airsoft Canada, the key improvement here is that it reduces wear and tear on the firing pin, which in the long run prevents part breakage.


There is one downside, which is that now the reduced friction and wider channel make it easier to accidentally trigger the valve, but with the shells packed as per my tutorial above it's not an issue since the collective mass of the payload resists the valve moving.


So, I went and applied this mod to my other 34 shells, and they all seem to be working great. It doesn't take a lot of work- unscrew the shell base, remove the O-ring, drill it out with a 1/4" bit, remove all shavings with a toothbrush, reinsert O-ring, reinstall base. Simple.


Also, if anyone is still using 12g CO2 cartridges to fill the shells, stop. They're really, truly awful for this application and seem to only deliver gaseous CO2 instead of liquid thanks to their minuscule volume. Unscrew the 12g adapter, screw in your choice of full-sized CO2 tank, marvel in the increased power and reduced cost of operation. The shells consume a lot of CO2 when filled with liquid (I got about 100 fills out of a 12oz tank before it started filling gaseous CO2), but the power difference is absolutely worth it, and if you live near a store that will refill your tank it's pretty economical.

Edited by CatgutViolin
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Forgive me but I am having a hard time visualizing exactly what part is drilled out? :o


I mean, I think I do, but clarification and picture ref. would be great :P 


Also regarding the 12g capsules, I tried the 88g ones and found it worked worse, and from where I am and the prices, was more expensive as well.

Edited by NonEx
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Yes, although it may be even cheaper to get CO2 refills from other places, like bulk gas supply places (what in the UK would be called 'plant hire' shops would be able to tell you where your nearest one is), home brewing supply places, fire extinguisher service places, and even aquarium supply places. Any online forum for aquariums, paintballers or home brewers will be able to tell you how to find the cheapest CO2 refills local to you.

Edited by PureSilver
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Forgive me but I am having a hard time visualizing exactly what part is drilled out? :o


I mean, I think I do, but clarification and picture ref. would be great :P


Also regarding the 12g capsules, I tried the 88g ones and found it worked worse, and from where I am and the prices, was more expensive as well.


I knew I should have taken a reference pic before drilling out all my shells. Here's an unmodified shell:




Notice how the valve stem is a perfect fit for the channel that it rides in. This works fine when they're new, but the shells I have that were heavily used had nicks and burrs in the channel making the valve movement gritty and stiff. As well, it's a tight fit for the firing pin, which over time can apparently cause damage or even breakage, and the way the firing pin grips the shells makes it a little harder for them to extract.


If you look at my shell above, there's a gap between the valve and the channel. It's a minor difference since a 1/4" drill bit is just a little bit wider than the existing channel, but it makes a big difference in operation. They trigger more smoothly, seal themselves more quickly when loaded, and eject better, tumbling end-over-end like a real shotgun hull.

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Right, that's what I thought it was. Just don't want to drill in the wrong place :D


Maybe just running a file around the inside edge would work too instead of drilling it ? :o


For reducing friction in the channel, definitely, but you need to make sure the surface is deburred and polished, which could take a while to go through successive grits of filing/sanding. Considering the other benefits this modification provides, and that it takes about three seconds for a drill to go through the channel, it seemed like an easy choice to me. Keep in mind the valve stem doesn't actually seal against the channel, it seals against the O-ring that rests above the channel, which is significantly oversized, so this modification doesn't compromise the seal at all.

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Ugh, dat price .


And the receiver has a different type of mount for the magazine tube so it won't be cross compatible. But the current magazine tube cradle setup on the APS CAM870 is pretty poor. Like I said 2 of my 4 set screws have stripped :(

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FRP made it so the tube is more similar to real steel (screwed on instead of welded), I think the price is understandable considering the amount of CNC steel involved.. but since I barely use my 870 as it is... can't justify a kit like that even if it's half the price. 

Edited by blobface
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$5.00 for a fill of CO2 from local paintball stores, and this one "parts store (Canadian Tire)"


HPA is usually free, but often they "jew" you and charge $5.00.

Air might be free but the cost of an air compressor isn't, nor is the cost of the electricity to run it, the premises to house it, the staff to operate it or the insurance to cover damages just incase something goes wrong so I don't think it's unreasonble for somewhere to charge a small amount to fill a HPA bottle, if you get it for free you should be considering it a bonus and not the norm imo.

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  • 3 weeks later...

Did some maintenance on my shells this weekend. Took a while.


Disassembled all of them. Cleaned all parts in soap and water.

Hand dried with micro fibre cloth.

Let o-rings soak in silikone oil while I worked.

Cut maintenance cut/slit in the primer end of all shells for easier removal of the rim cap.





Here's how I removed the rim/cap before making my service cuts.

Removed the outer plastic shell first.

Wrapped inner metal shell in a micro fiber cloth for added friction.

Clamped the shell down.

Then used a plumbers wrench to remove the rim/cap.





Made service cuts on all of the rims in the primer area.

5 seconds with a Dremel cutting disc.

Make sure to clean out the aluminum dust from the cap. I used Q-Tips and ran them through the primer hole.

Made a dis-assembly tool from an extra Dremel attachment wrench I had.

Works well. But the aluminum is very soft so if you over torque it the cut can deform.

But better than messing up the outer edge of the rims with a wrench. :o





And finally a pro-tip on how to easily and quickly de-burr and re-finish the rims of your APS CAM870 CO2 shell rims!


I used a socket bit that just fit inside the shell.

Mounted it in my drill.

Stuck the shell on there and spun it up.

Then ran a file around the rim edge until the burrs were gone.

Be careful not to remove too much though.





The internals of the APS CAM870 CO2 shell.



Edited by NonEx
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