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Old 01-04-2015, 02:09 AM
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MP5 Mid-Cap Magazine Modification Guide

Below is a guide on how to disassemble and reassemble the CYMA Airsoft 120-Round Mid-Capacity Magazine for M5/MP5 AEGs. (Difficulty level 3/10). This guide can be used to simply take the magazine apart for maintenance, clear a jam, or to replace/modify internal parts.

My Problem: the magazine was double/triple/quadruple feeding my ICS MP5 A4 80% of the time (it is 8 years old, I am getting back into airsoft after I stopped around age 16). At first I suspected my hop-up/bucking was to blame, but my other magazines were feeding perfectly. I recently bought this particular magazine from Amazon and it was the cheapest MP5 mid-cap available so I suspected the magazine may be at fault.

Solution: replace the spring in the top of the magazine that controls the tension of the lever stopping the bbs from coming out and trim the existing internal spring that pushes the bbs through the magazine. (cost: $0)

Result: only double feeds occur now and they only occur about 30% of the time. That number is not exact as I have not tested it extensively yet because I ran out of bbs, check back later this week for exact results.

Below are step-by-step instructions to disassemble and reassemble the magazine as well as to perform the solution described above. Remember to place all small parts in a cup or something so they do not get lost during the process.

First, take a firmly pointed object and a hammer (or something sturdy) and push the pin out near the top of the magazine. If the pin resists several tries or will only come part way out, then attempt to extract the pin from the other side. The pin has a larger end that cannot be pushed through the hole all the way. The larger end has some slits in it all the way around the shaft while the smaller end is completely smooth.

Once you have pushed the pin out a bit from the smaller end, pull it the rest of the way with a pair of pliers. The magazine will now pull out of the top of the magazine shell.

The magazine has several screws along one side (they are all identical so no need to remember which one goes where). The first screw you should remove is the one from the small hatch. This small hatch is the “door” to the back of the long internal spring. Upon removal of the “door,” one of the two springs will likely eject from magazine (most likely with some force). A small black plastic piece that joins the two springs will also likely fly out or be rattling loose inside the magazine. If rattling around, dump that plastic piece out if possible.

Begin taking all of the other screws out in no particular order. Once the screws near the top of the magazine are removed, the second internal spring as well as the small bb stopper lever and its small spring will fly out (literally) of the magazine. It is best to have the magazine pointed down inside a cup so these pieces are not lost when they fly out.

Now that all the pieces are out it is time to trim the longer spring that flew out first. I trimmed approximately 3.4 inches off only the spring end that rests against the hatch. When at rest, the spring has approximately 25% more length than the total length needed to fill the spring chamber. Set the larger springs off to the side.

The small bb lever spring can be replaced by almost any pen spring. Thus, find a pen with a push-down spring system. You can use wire cutters to trim the pen spring. Some pen springs will be provide more tension than others so take a couple apart and test different springs and lengths by putting the magazine partially back together with just the lever and the spring installed, then pull back the little lever knob back to test resistance and clearance.

You are ready to reassemble your magazine. Place the bb lever and the small spring into the side of the magazine that has a small lip where the back of the spring meets the magazine. Now carefully put the other half of the magazine on the one with spring and lever. The small lever and spring will likely slip out from your fingers a couple times and fly across the room so be ready to look for them as you put the halves together.

Put all the screws back into the magazine (remember the highest hole on the side of the magazine is for the push the pin that attaches it to the magazine shell), do not install the spring hatch and its corresponding screw.

Attach the two long internal springs with the small black piece and slide the side with the attachment (bb pusher) at the end in the hatch first. Continue to push the spring through until all of it is in the magazine then put the hatch on and screw it in.

You are ready to reinsert the magazine into the magazine shell and push the pin into the holes which will attach the two pieces (small pin end in first). The magazine is ready to be used/tested. It took me many tries of spring combinations and lengths to find one I was happy with, I will likely continue to test different combinations to get the feeding perfected.

My conclusion from this project is that cheaper magazines have the internals that will work at least moderately well if adjusted correctly. However, their initial setup is usually not perfected/extensively tested which causes things like to strong/long of a spring to be used to push the bbs through.

I have pictures of the process if anyone is interested in seeing them, but tonight I have a slow internet connection and cannot upload them.
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Old 01-13-2015, 04:09 PM
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This may e a good guide for all magazines that double feed. I too have had some problems like this but never thought it was the mag causing this. Now do you know what causes the first feed bbs from each mag to "plummet?" I say this beause it sounds like the gun is dry firing, but it's not. It'll shoot a bb about 50 feet very slowly, this happens at the top of the mag for about 10-20 rounds. I've noticed it happen with newer mags and it stopped after I left the mags loaded for a while. But then I've had mad that are well broken in and still do that depending on the gun I use and different mags. I guess I just have bad luck.
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