Steely Slide Stopping Success

Is it wrong to be this exctited about a fairly small piece of technical innovation? If it is, I don't want to be right.

Around a year ago, I bought a second hand, run down KJW KP-08 with the hopes of fixing it. The four CO2 magazines that came with it had leaky valves, but most other things seemed to be in ok-ish working order. I put the gun and mags in a box and stored them for later. Once I now finally got around to replacing the valves and testing the magazines, I was faced with a new problem.

The old, original slide stop was so worn down that it would not stay put in the gun when shooting, and eventually decided to attempt evacuation at the most inopportune moment. The result (as best I can deduce and reconstruct the events) was that the slide slamming backwards hit the stop, and broke it in two.

At first I thought of just getting an original replacement part, but I've had my fill of pot metal parts lately, and decided to shop around a bit. That's when I came across this KF Airsoft steel slide stop for the Hi-Capa. I thought it brilliant, as I would not have to worry about it breaking again. Once it arrived, though, I was pleasantly surprised even further.

In addition to the stronger-than-original build material, the take-down pin is not a single piece, but a sleeved structure. What this allows is for the weight and force of the slide to rest on the sleeve, leaving the actual slide stop lever to rotate freely inside. In other words, you can have the take-down pin as tight as you want without it affecting how the stop itself functions. This is simply brilliant. I don't know who originally designed this, but it's damn marvelous!

As with all things airsoft, though, some modification was necessary.

As seen in the above image, there's a metal nub protruding from the inside of the stop, which would hit the feed lips and the side of the magazine, preventing proper seating and functioning. So, what else was there to do but break out the file set and get to work?

I filed down a bit, tested the fit and worked until nothing pushed against the magazine.

As a result, I ended up taking down the protruding nub entirely and shaving the backside of the retaining tab as well in order to secure proper fit.

I reassembled the gun and had a test fire. I'm now getting a very positive lock with this part. It's better, in fact, than the original one, and it cost just a few coins more than an OEM part!

It's (sadly) not everyday that you come across airsoft parts that surprise you this way. I'm pretty stoked this one did! If you have any similar experiences, please do share them below!

Fixer-upper Part 4: Classic Army P90

Here we are again. A broken gun up for grabs for cheap on a For Sale site. And grabbed it I did.

Patient: Classic Army Sportline P90
Symptoms: "Has had some electrical issues, been to a tech but stopped working again quite some time ago and has been unused since"

I've never owned a P90 before, but it has been on my get-one-some-day list for some time. This one is from the Classic Army Sportline series, meaning the externals are mostly plastic. Now, the real P90 is mostly plastic as well, so it did not bother me that much, even though usually I'm a stickler for realism in materials. Compared to a real P90 the only thing not of similar materials is the upper receiver. The outer barrel and flash hider are metal, as are the optics rails. Furthermore, metal uppers should fit right in if I ever want to get one.

The gun came with a Swiss Arms C-more style red dot (with a missing front clamp), two hicap mags, two NiMh batteries and a dumb charger. The internals had been upgraded to some degree, but the previous owner did not know much about them. In his words, he didn't know what had been done, the gun had been to a tech twice for electrical problems and now just would not fire at all.

Troubleshooting

It didn't take long to find out that the batteries had simply died. With a fresh 7.4 V LiPo this thing came alive, if only on full auto. Something was wrong with the semi function, and I could hear a rattling sound coming from the inside when the gun was tilted back and forth.

Externally everything seemed good apart from a small crack in the rear of the receiver. The two sides of the front grip also did not quite stay put due to a screw having lost it's threads. Nothing to hinder functionality, that is.

The P90 turned out to be exceptionally easy to disassemble. As you might know, my first gun was an AUG. That was very easy to gut, but this one was even better.

After popping the back plate, you see two screws. Take those out, remove the plate they held down, and the gearbox comes out.

The P90 uses a less common V6 gearbox, so replacements and spare parts are somewhat harder to come by than on your average AK or M4.

The upper receiver can also be removed simply by pressing a rectangular button on top of the receiver and sliding the whole assembly out. I could not help but fall in love with the design straight away.

The modularity was not limited to the externals. The gearbox comes easily apart as well, separating the motor cage, wiring and trigger switches into an assembly away from the main body. No wires to stop you from working, and you can test everything without inserting the GB into the gun.

The problem with the semi auto not working quickly became apparent once I peeked into the trigger switch assembly. A part had broken off from the trigger trolley (seen above still wedged below the trigger contacts). With the piece off, the trolley would simply skip over the trigger switch, not move at all and thus not engage the contacts.

The rattling I heard when tilting the gun was not an extremely short spring as I though at first (the gun chronoed just above 0.6 J), but rather the broken stem of the plastic spring guide sliding inside the spring.

The two main problems had been identified, and I got to work fixing them.

Fixing-upping

In addition to fixing what was broken, my plan also included swapping the plastic bushing for steel ones and re-shimming, fixing AOE, installing a MOSFET, and putting in a flat blade fuse and deans connectors. My plan was to build a CQB beast with a high ROF and moderate power.

Swapping out the broken spring guide seemed rather straightforward, as I quickly found a steel spring guide in my spares drawer. The V6 box takes V2 spring guides, which makes it easy to replace. Or so I thought.

A couple of test shots later the spring was compressed into the piston, which in turn was stuck in the rearward position. In case you've never done it, let me tell you that disassembling the gearbox again with this kind of a mine inside is just lovely. I managed to get it out without issue, luckily, only to have it get stuck again (because of course I had to try it again). It was pretty clear that the spring guide would not work here.

I scavenged another spring guide from an M4 parts box I had lying around, waiting to get assembled. It was otherwise similar, but the end was tapered and, more importantly, it had a diameter that was 0.21 millimetres smaller. The one fifth of a millimetre was all that was needed, the spring did not get stuck. The spring, as well as I, was free to move forward.

Swapping out the plastic bushings for steel ones was pretty straightforward, but they did sit quite low in the shell, and I had to use more shims than I've ever had to before. At some point I began to question whether or not I was doing something horrendously wrong, as the the combined thickness of the pile of shims on the spur gear crossed the 1 mm mark. It worked swimmingly, though, so that's tolerances for you.

Trying to fix the angle of engagement on the piston turned out to come with its own set of problems. The piston head was attached with a tiny nut sitting free inside the piston. I could unscrew the head with ease, but lacking a socket wrench for ants I could not put it back on. Who makes these things? I opted instead for an aluminium double sealed head I had lying around.

My problems with the spring guide had apparently resulted in some structural problems, since at some point during test firing the steel tooth broke off the piston. Luckily I had an old spare nylon piston with it's own plastic piston head that went in after a quick AOE fix, similar to the one pictured above.

My first attempt at fixing the trigger trolley consisted of glue and a several thin layers from a piece of paper towel. I figured a glass fibre style layer cake of material and bonding agent would result in a strong base which I could then file into shape. 

Too bad the plastic wasn't very glue friendly. The glue soaked paper held together fine, it just would not stick to the plastic hard enough to withstand the strikes delivered by the cut off lever. The same exact thing happened with various attempts made with super glue, epoxy and even chemical metal. This was one piece of engineering I was not exactly happy with. A thin piece of plastic subjected to repeated strike forces sounds exactly like a recipe for success.

Since the original plastic was a no-go, it was time to fabricate a stronger part. I chose a piece of sheet metal for the job with roughly the same thickness as the original plastic. After tracing out the shape of the trigger trolley, I cut it out, filed it down to size and rounded off any rough edges.

I drilled a few holes (with a 1.5mm drill bit) into the metal, filed down the original trigger trolley, drilled some holes into that as well and roughened up both surfaces, hoping the epoxy would finally bond well enough. I chose to make the holes canted every which way so that once the glue set, the pieces would not come off each other so easily.

To further address the issue, I cut down the trigger contacts so that the trolley would have more freedom to move up and down (the top piece is cut to shape above, the lower shows the original shape).

Everything was working pretty nicely apart from the fact I was getting triple and quadruple shot bursts on semi. The culprit in the end turned out to be my upgraded trigger trolley. The sheet metal was not as thick as the plastic, and thus the trolley was able to sit higher in its rails before disengaging. This in turn made it so that the cut off would not lift it out of place until the trigger was fully pressed down. I fixed this by epoxying another piece of the sheet metal onto the cut off and filed it to size. No more problems with semi auto! 

To round things off, I made a basic DIY MOSFET out of an IRLB3034 and some resistors. The middle prong is cut off and the negative lead is attached with a small bolt and nut to the back plate. Sturdier attachment, better flow of current.

Wiring up a MOSFET on a P90 can be done exactly like in the AUG, since the trigger assembly is the same. There's one switch and a pair of contacts for the semi, and another for full auto. It's only the movement of the trigger that decides whether the gun fires semi or full auto. On the AUG it's up to the shooter, on the P90 the fire selector limits the movement of the trigger.

All the extra bits and pieces fit in without issue and the gun was mechanically ready for service.

One final fix was to repair the cracked receiver. Since the material is ABS, you can forego glue and use pure acetone, as it melts ABS. My end result is a bit sloppy, but with an unhurried approach, slowly wicking the acetone into the crack, you can achieve a brilliant result. While mine isn't aesthetically as pleasing as it could, the upside is still that the plastic is again one single piece as it was when moulded, not two parts held together by an adhesive layer.

With an 11.1 V LiPo this little beast is pumping out 33 rounds per second at 0.92 J. Right on the money, if you ask me. Now I only need magazines that aren't hicaps and can still keep up with that.

Questions? Comments? Anything you'd add or like to know more of? I'd love to hear from you! 

Pouch Painting

If you've ever bought gear from more than one manufacturer, you've most likely been there: Colours don't match. Olive drab especially seems to be a complete no man's land when it comes to colour coordination. They're all supposedly the same colour, but when you place them next to each other, you will certainly notice they're not.

You can always go out in your non-matched set, or grab a can of spray paint and go to work. Here's a quick primer (yes I went there) on how to get your garb to match.

The picture above shows quite clearly just how different the concept of olive drab can be. The RRV replica underneath is from Miltec, and the various pouches are from Pantac, TMC, Condor and from an unbranded Chinese manufacturer.

Painting nylon is fairly straightforward, just apply several thin layers as you would do with any other spray paint project. The de facto brand that people enjoy using is Krylon for its consistency but I went with a camo colour series from my local car parts etc. retailer, Motonet.

Here's a great example of "do as I say, not as I do". I went a bit overboard with the spraying on this TMC radio pouch, and you can see the otherwise matte paint is starting to glisten on the lip of the pouch. Otherwise the result is pretty good. You can clearly see the difference between the painted part and the so far unpainted fastener on the top right. Do note that the paint interferes with velcro to some extent, so try to avoid spraying large quantities over such surfaces if you want to retain the stickiness.

Some parts, such as the crease on the pouch above can be a bit problematic if you want an even coat. You can, however, always spray and then rub the paint in with your fingers, for example.

You can also use gloves while doing it. Assuming you're not too dumb and/or excited to remember such things, of course.

Really getting there after only a short while. I'm sure the father-in-law doesn't mind spray paint on his lawn.

The end result after three(ish) light coats. The AK pouches were left unpainted to be used as reference. I left the paint to cure overnight before using the pouches.

Do you have experiences in painting your gear (or guns)? Let me know in the comments!

"Lazerrr"

In case you saw my Instagram yesterday, I went to a Hackerspace where my friend is a member and we did some laser cutting. The place is amazing, they have all sorts of machines available to members. I'm definitely joining, because so many things will be easier with proper tools and space!

The quick project I did was cut some Sorbothane pads to use for AOE correction and shock absorption. You may remember from an earlier post how the pads I made by hand looked. If not, here's a refresher.

It's not exactly flattering, but that's what you get. Sorbothane is a pain in the ass to cut, since it is so elastic. The material wants to escape scissor blades and punches, and thus the results are quite crude.

Enter futuristic technology! The laser cutter works on vector drawings and produces results with tolerances down to parts of a millimetre.

On the right-hand screen you can see the simple vector drawing. The left-hand screen shows a live camera feed from the cutter, below. The machine lid is emblazoned with an appropriate warning label. Safety first, after all!

After a few test cuts we had the settings nailed down and could get to work. If you're planning on doing something like this, know that the sorbo creates a bit of smoke when cut and the material melts where the beam cuts it, turning into a sticky goop. Luckily, though, it washes away easily with just plain water.

The end result is from another world when compared to anything I could cut by hand. A 150x150mm sheet of Sorbo that had been used a bit before netted me about 35 pads all ready to use. You could certainly get more if material isn't wasted on testing and cuts that end up not using all available space. Still, compared to buying these one by one, this was brilliant. Plus you can alter the size to taste.

This was a very nice little project and it was easily completed within just a few hours. The resulting pads will last me quite a while.

I hear the laser also cuts acrylics, so I'm already planning on creating some lens covers in the future.

Stay tuned and play safe!

Machinegunning - Phase Two

In the previous post I introduced the project, and have now finally had time to actually get back on the horse, so to speak.

The previous post ended with a to-do list as follows:

• Replace internals (I already have a new spring and some leftover torque gears [21.6:1] as well as a full cylinder, a new piston and head, o-ring nozzle and steel bushings)
• Wire to the rear, install MOSFET and deans (I have a G36 collapsing stock that will house the large battery)
• Fix the hop-up (the current one is pretty dicey, I'm planning on installing R-hop for range)
• Pretty up the externals (I intend to get rid of the engravings somehow, tips welcome)
• Acquire battery (3600mAh 7.4V LiPo on order) 
• Acquire bipod (standard G36 bipod on order)
• Acquire magazine (an electronically run G36 C-mag would be ideal, tips on brand welcome)
• Rewire magazine so it feeds when the gun fires and runs off the gun's own battery

Since last time, I've managed to acquire all the requisite parts and got well under way on the building. Let's break down the list above step by step.

Internals replacement

I was going to go with what I thought were Modify 21.6:1 torque gears from a boneyard gun, but it later turned out they were actually standard 18:1. I had based my assumption of the gear ratio on a calculation derived from the RPS of the abovementioned gun, but it later turned out the RPS was a result of poor electric conductivity in the wiring harness, i.e. the gun ran slower than it should have. A curious aside, but let's move on. 

I had in store a set of 18:1 steel XYT gears that I went with in the end. The spring I installed was an SHS M150, which I hoped would be putting out around 2J of power with a sorbothane pad installed. I went mostly with SHS for other parts as well. The cylinder, piston, steel spring guide, selector plate, steel bushings and motor were all of SHS make.  

I followed the to-do list above otherwise, but found out the metal nozzle with an o-ring I had for a G36 did not fit this particular gun.

The nozzle in the front position was woefully short, so I went back to the stock nozzle the gearbox came with. As it later turned out, that did not hinder performance much, if at all.

The selector plate was slightly too thick to fit the rails, so it had to be filed down slightly.

I also thinned it down on the parts that touch the rails to make it run smoothly. A bit of silicone grease finished the job and made the selector switch turn extremely smoothly.

Otherwise the building of the box was rather straightforward, but I'd be lying if I said closing it with the M150 spring was anything but challenging. I think I got everything to stay in place on the fourth or fifth try.

And then the motor would not turn the box all the way over. After considerable time and trouble I finally figured out the problem had to do with there simply not being enough physical space in the box for the spring to wind fully, as I had used both a spring guide and piston head which had ball bearings. I opted to pull out the ball bearings from the piston head and replace them with a simple metal washer. Once I got the box back together again, this time I got it to turn over, finally. It was time to pull out the old wires and rewire the whole thing.

Rewiring to the rear

To begin with, I desoldered the old stock wires that had run to the front handguard. One very positive thing about the V3 gearbox is that the wires attach to the outside of the box, so I could do all this work without opening the gearbox back up again. The plan was to build a completely new wiring harness and install a MOSFET, a fuse and a deans connector along the way.

The original wiring was pretty shot up to begin with, and I had specifically purchased silvered 16 AWG wires that had a PTFE jacket for this project. The overall thickness of said wire is significantly less than same gauge wire with a silicone jacket. It is also stiff, so it keeps its shape when bent, which is great for threading it through small holes and fitting the gearbox in the gun's frame.

I did some measuring to see how much wire I'd need to complete the harness and have it run all the way to the rear of the stock.

The measurements didn't need to be completely exact, but with wires too short I'd run into trouble trying to hook up the battery later on.

There are plenty of guides on building DIY MOSFET units, one of which (in Finnish) I followed. Rather straightforward. The unit itself was an IRF3703.

Sadly the unit (a cheap Chinese knock-off, as I later found out) did not last long in use and in the end I replaced it with a much better IRLB3034. The "fun" thing about MOSFETs is that they typically fail  (burn out) so that the circuit remains closed, which means the gun will fire full auto, regardless of trigger pull or selector position, as long as the battery remains hooked up. That's not really something you want to happen mid-game, so I suggest forgoing the cheapest pieces on ebay and getting your components from a proper electronics store.

This build was fantastic in the way parts almost magically fit together. I used a 30A blade fuse in the build, and completely by accident found out not only that the holder was exactly the correct size to fit through the opening in the rear of the stock, but also that it would fit partway out of the side of the stock where it contacts the receiver when folded, making the removal of a burnt fuse very easy.

The battery also fit in the compartment with the MOSFET, fuse and wiring like a glove.

With the wiring and internals otherwise done, it was time to move onto the hop-up.

Hop-up bucking replacement and R-hopping

There are plenty of guides on how to build an R-hop, so I won't link any particular one here. For this project, I opted to use silicone tubing of my choosing and cut it into shape instead of buying ready made patches.

To build an R-hop, you basically cut a patch that will fit in the barrel window and glue it in place. Next you take your bucking, flip it around and cut and sand down the nub so that the inside surface is flush.

I used a green G&G bucking which I pulled over a spring guide in order to have a nice, hard working surface. Once flat, the bucking was once again flipped the right way round and placed on the barrel. I used some silicone grease on the outside of the bucking in order to get it to slide effortlessly into the hop-up mechanism.

Bipod

I went and purchased an original JG bipod meant for the G36 to use in this project. Sadly, it came without any attachment hardware, so I had a gun and a bipod but no way to connect the two.

After rummaging through my hardware drawers for a while, though, I came across an interesting nut and bolt that were leftovers from an IKEA wardrobe installation, meant for holding two separate cabinets together side by side.

As if by miraculous coincidence, these two fit the hole meant for the bipod not only in thickness, but also in length just perfectly.

With the bipod in place, the gun was as complete as I was going to be able to make it at this point. I topped it up with a non-magnifying red and green dot ACOG I had set aside just for this project.

Testing and wrapping up

I now had a working gun that I could finally test. The G36 has a nice, large receiver, so all the wiring and so on fit in without too much effort. In fact, it is one of the easiest AEGs to take apart and put back together that I've come across so far.

I set up my chrono for a test firing session so I could see how the gun would fare. 

My expectations (and local machine gun power limits of 2J) were exceeded rather wildly. The SHS M150 spring was giving out way too much power, and has to be substituted for another if I intend to actually field the gun at some point. For now, though, I'll keep the spring in and test how the R-hop works. It might also be that the spring loosens up over time, so I don't want to rush in to swap it just yet.

I already also have an electronically run C-mag that fits the gun, but it still requires some extra work. In the end, though, I will have wires running from the gun's motor to the mag so it will wind whenever the trigger is pulled, thus obviating the need to push a separate button or to have batteries installed in the magazine itself. All in all, though, most of the work is already done and the gun is already usable!

The externals still also need a bit of work, as the ABS plastic has worn down some and the surface has ugly engravings on it. At this point I'm planning on using a sponge with acetone to recreate the uneven surface of the original parts. Any tips on that are more than welcome. 

For now, though, stay tuned, and if you feel like it, do drop me a line regarding anything relating to this build or anything else on the blog!