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Thread: My GSG-522 "build"

  1. #1
    Sergeant RennFab's Avatar
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    Default My GSG-522 "build"

    Starting a little thread about this build of sorts. Have been nagging a good friend for years about selling his to me and he finally bit. Second gen model 522 in complete bone stock trim. Not being able to leave well enough alone, I immediately dug into the rifle and started fixing all the little "bugs" the platform has and adding a few custom bits. This will be an updated in-progress thread as I move along with it.

    Started first by picking up a navy SEF MP5 lower and safety assembly. The lower is a direct fit to the GSG frame and has an even tighter tolerance fit to the main housings. More ergonomic grip, little nicer texture, and stiffer overall. The GSG fire control group will fit this lower, you simply need to carefully notch the side of the housing to fit the serial plate. The MP5 safety takes quite a bit more work to get to properly function in the FCG.

    Stock GSG vs SEF lowers and safety:




    To some the GSG has a few bugs that can be worked out, some more serious while others are more nuisance. I decided to nip them all in the butt at once. For starters is the magazine safety, or the inability to fire the rifle without a magazine in place. Most eliminate this feature by simply removing the trigger trip plate from the FCG, however this creates a somewhat loose magazine in the housing as there is no longer spring pressure from the plate acting on the mag body. The simple fix is to remove the plate and trim the part that prevents the trigger pin from rotating up, then reinstall it in the FCG. Red portion indicates material to remove





    The next modification is the one that actually prompted me to do almost all of this to begin with. Known as the "strut mod" it's actually a fairly simple thing to do and one that I recommend you have completed if you're up for the task. The reasoning behind this mod needs to be explained to understand it. The hammer doesn't have it's own firing spring like an AR, but it's rather wrapped around this strut part that forces the hammer forward, In normal OEM fashion, this strut forces the hammer forward and it carries past the strut stop point to strike the firing pin but then returns to a setback angle of about 10 degrees or so. See this picture for normal hammer position:



    In normal fashion the bolt provides some of the total spring force that holds the bolt closed against the breech during the firing sequence. It has been shown however that this total force is a bit on the light side. Not normally and issue in most rifles but on the GSG it has been show to potentially lead to catastrophic failure of the barrel chamber as brass is being extracted far too early which chamber/barrel pressure is too high. It's leading to split chambers and broken bolts, but can also just be a safety issue as well all things considered.

    So the simple fix it to mildly adjust this strut to allow more forward movement of the hammer and this apply more pressure to the back of the bolt. It's a rather simple mod if you're not afradi to dive into the FCG, but you do need to take your time and go slow. Once the FCG is disassembled, you'll need just a small 1/8" round file. On the head of the strut are two notches. The upper notch rides on the pin in the hammer that forces it forward, the lower rides on the larger hammer pivot pin. This is the one you will want to slowly remove material from. It's best to lightly clamp the strut in a vise and to keep the file flat. Your intent is to remove material from this notch so that the hammer sits in a near vertical rest position. The first pictures shows where you will remove material from, second of the hammer in it's new rest.






    Next post.........fixing the chunk trigger on this rifle
    JVG, meketrefe, ODgreenAK and 1 others like this.
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  2. #2
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    I think I have a spare SEF lower you can have if you need it for experimentation. You just have to pay shipping and it's all yours. Shoot me a PM if you want it.

  3. #3
    Sergeant RennFab's Avatar
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    The GSG-522 trigger. At best it's a clunky, super long two stage pull trigger with a feel that's best described as sliding two pieces of rusty steel plate with peanut brittle in between. Yeah, size that one up! Being that I really want to try and make this rifle as accurate as possible the trigger just had to be fixed. Right off the rip I'm going to state that if you do not know how a trigger works and have little experience in working with them you really should leave this mod to a gunsmith. Before starting this modification set, I measured the trigger, cleaned and properly lubed, at just a hair over 6.5lbs and VERy gritty in the process.

    Lets start with the FCG:



    You have(top to bottom, left to right) FCG bodies, trigger reset plate, trigger group with sears and disconnector, hammer, hammer strut, body bolts(upgraded allens here), sear spring hammer spacer, hammer preload spring, hammer pivot pin, hammer spring bushings, hammer strut spring, MP5 safety lever, and the magazine safety plate. The trigger and magazine plates have their own preload/tension springs but we will disregard these components for now anyway.


    First step is to remove a redundant safety feature on this rifle and in turn remove some material that causes undue friction in the trigger pull. This feature is a firing pin cross bolt, located in the bolt itself. The "BCG" in this rifle is a two piece fixed housing/carrier that holds the bolt and return springs. Separate the halves vie phillips screws(upgraded to allens in this rifle now) and two T10 torx. Remove the bolt mechanism, and remove the two REAR torx screws at it's top. On the left side of the bolt you will see a domed `1/4" diameter pin. That's the cross bolt we are going to remove:




    On the ejection side of the bolt you will will see a small hole with a 1.5mm allen set screw that you will want to remove and set aside. Back over on the left side of the bolt you will see a small 1mm dia hole. Now, loosen the single torx screw on the top of the bolt a few turns, no need to back it out completely now. Taking a small paperclip, you will now push the firing pin retaining pin out of the bolt from the left side by pushing through that tiny hole. WHILE DOING THIS, keep downward pressure on the top plate of the bolt, as well as slight back pressure on the firing pin between the two guide rods at the back of the bolt. When you release the retaining pin, the firing pin will want o move back and up. It's not super high pressure, but you still don't want the thing to just pop apart on you.

    Once the retaining pin is out and the paperclip is removed, place a finger over the domed cross bolt and SLOWLY let the top bolt plate up. The firing pin should rise a bit with it and when it clears enough, the cross bolt will pop out towards your finger. Slide that out, along with it's spring and push the firing pin and top plate back down on the bolt. insert and lightly tighten a couple of the top plate screws, then reinstall the firing pin retaining pin into the hole and install the little 1.5mm allen set screw as well. DO NOT use any locktite threadlocker on that set screw, but it's a good idea to put a small amount of high temperature liquid teflon on it( IE locktite 565, 567, 5770, etc all work). You may have to push the firing pin forward a bit to get the retaining pin back in it's slot. Afterwards, remove each of the three top plate screws, degrease, and reinstall with a little drop of threadlocker on each. I've stated before, you can replace the OEM high torque phillips screws with g12.9 metric M3x0.5 allen cap screws. When done, clean and assemble the BCG housing, taking care to properly install the return springs with the narrow taper facing the bolt/wide end to the back of the housing.

    There are other modifications you can do to the firing pin to aleviate light strike issues, but this rifle did not suffer from this problem and as such I won't cover it here right now. Here is the cross pin and it's spring removed:




    With the BCG addressed we move back to the FCG and the trigger reset plate. This large plate is what sets the trigger assembly into it's stages, and at the same time acted on the cross bolt we just removed. You can now remove a good portion of the plate that now does nothing more than add undue weight and friction to the trigger pull. The entire top portion of this plate depicted in red can be removed and the cut edge filed and polished for zero burrs:




    The next step is to remove some of the GSG's ungodly long trigger pull/travel, and prevent it from being set into it's "1st stage" of pull. In the picture above you'll see a green area next to a slot. This is material that needs to be added(IE welded) in and filed to adjust the maximum travel the plate can return and thus reset the trigger. This is another step that needs to be done slowly and carefully as this can be overdone and make the trigger very touchy due to improper sear engagement. You will need to assemble the FCG and record the triggers full release state, however if you're performing this mod you should already know that and know what you're doing!

    The cutout in the bottom of the plate with the back radius is the part that actuates a lever in the side of the FCG, which ultimately resets the trigger via a pin in the trigger body. As you can see....alot of moving parts where friction all adds up. The side of the FCG where this plate slides and the reset lever:





    Done correctly, you can effectively reduce the travel of the trigger from full rest to full release by 50-60%. Seen here in this picture, I show(roughly) the triggers state from original full set, to the new modified set as well as the full break. Note, method of measurement here is solely to depict in visual format for you, not true way to measure.





    Once you have successfully modified the reset plate, you'll want to polish the back face that touches the FCG body, the inner ridge in the reset lever pocket, and the front(outer) face area near the two slots that the bronze bushings ride against. Other effective means of reducing friction by reducing material contact have be done to the FCG body under the reset plate but everyone has to keep a couple trade secrets to themselves right! so I won't rightly post them up here for all to see just yet



    The sear and related work is next. The components in this FCG are quite nice. Quality pieces with decent machine work but still have room for improvement. Here is a picture of the what I dub the "trigger unit" positioned in the body:




    Three major components in the trigger itself: The disconnector and it's spring, the sear and it spring/lift rod, and the lower safety lever. There is a single spring that sit in between a small pocket and the lower front lip of the sear lift rod but I have it removed here as to not misplace it.

    If you have modified the FCG and reset plate to limit the full forward travel of the trigger, you effectively make this piece redundant. Being redundant, it's an unneeded part that's adding friction to the pull. It's simply removed by driving out the lower pin and pulling from the trigger. The pin sits pressed fit into the safety lever and not the trigger so you won't put it back in. Normally, this part prevents the sear lift rod from dropping prematurely by blocking the lower lift rod extension until the trigger has been pulled back far enough to begin disengagement of the sear. If you wish to retain this safety feature you actually need to add material to the front of this and machine it accordingly to reach underneath the extension itself. I am removing this part from my FCG for the time being, but am going to hold onto it for future use if I decide that the rifle really needs it. In effect, this is where good sear engagement comes into play, as you don't want the lift rod dropping for no reason.

    The disconnector sits off it's own pin in the trigger, which also doubles as the pin the reset lever pushes on. Not much if anything needs to be done here. The sear sits in the lift rod, and rides on the main pivot pin for the trigger itself. The sear has it's own pin and spring contained in the lift rod, and is staked in place so it's not recommended that you remove it from the rod(or lever if you want to call it) but you can remove the lift rod and polish the side of it to reduce friction in the trigger itself as well as any potential drag in the FCG body.

    The sear angle and engagement is good but the faces were less than desirable so I stoned them flat and parallel and polished them to reduce friction. After sub 1000 rounds through this rifle, you could clearly see the uneven wear. While I can't sit and give out spec details on what I did because every trigger is different, you again should know what you're doing if you're going this far into it and shouldn't need my explanation as is. While I still have a little more work with this yet, all assembled and tested I've effectively reduced the pull from about 6.5lbs, down to about 4lbs and more importantly made it super smooth and crisp. I could likely squeeze a bit more off the pull weight by messing with the lift rod spring and stoning a the sear differently, but I don't want this touchy and hair trigger like.
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    Sergeant RennFab's Avatar
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    update #3. Moving on to a little bit of cosmetic work, I decided the stock black color was a little plain jane for the build so I went and ordered a few different colors of duracoat. I chose Coyote Brown, Vltor FDE, and AirForce Digital Tan. Not entirely sure yet what I'm going to do just yet but I went ahead and stripped all the factory metal components down to bare metal by soda blasting them at my shop leaving a perfect texture to apply the epoxy paint.




    Next up I wanted to change the stock. For starters it's LOP was a bit on the short side for myself and two it's inherent mounting style on this rifle made it relatively loose. All commercially available stocks to fit the HK series rifle and/or the GSG platform didn't appeal to me and I was about to start CNC'ing my own adapter and creating my own parts when it dawned on me that I could adapt an existing stock to the rifle to suit my tastes, increase LOP, and stiffen up the rifle. I had recently completely a grease gun conversion on a friends HK USC and knew he still had the original stock kicking around so a phone call placed and a few hours later I picked up a pretty much new condition USC pistol grip/stock




    Start of the work involved putting both the original GSG stock and USC stocks in my vertical band saw and removing only the needed portions of both to be molded together:







    Next, I potted the formed webbing of the USC stock to give a more solid form to shape for a tight fitment into the remaining part of the GSG stock, shaped the part to fit, and formed a rough marriage of the two components. I also machined some billet inserts to center and lock the portions of the two stocks, as well as one for both the bottom of the SEF pistol grip, and the remaining portion of the USC pistol grip to allow me to rigidly fix them together via a countersunk allen cap screw:







    Thereaftter I moved onto blending and forming the components to look more uniform and flowing, and prepping the surfaces for the upcoming paint work that will follow:







    I have some minor custom work planned for the handguard as well as just like the stock I am not too fond of most aftermarket bits out there for this rifle.



    That's all I've got for the time being. Hopefully the next round of photos will be of some paint
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    Neat (and detailed) posts! Interested to see the next steps in the project.
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    JVG
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    amatuer. Looks and feels great. Can I buy my old GSG back when your done? Same price I sold it to you for of course, haha.
    "Laws that forbid the carrying of arms...disarm only those who are neither inclined nor determined to commit crimes...Such laws make things worse for the assaulted and better for the assailants; they serve rather to encourage than to prevent homicides, for an unarmed man may be attacked with greater confidence than an armed man." -Thomas Jefferson, quoting Cesare Beccaria

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    like it...

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    Great thread! I bought and modified a GSG 522...replaced the screw sets, HK push pins, HK hand guard and HK stock. This is over the top. Cant wait to see it when its done.

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    Sergeant RennFab's Avatar
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    Thanks guys!. It's actually a fun build that's taking a bit more than the typical nut and bolt AR type assembly and making my brain work a bit. I should hopefully have a majority of the parts in paint over the weekend and do a test assembly of the major components. I'm tossing around the idea of sending the bolt and carrier halves out to get nickle boron coated as well, why not right?!?!

    Some may have also looked at my other thread and put two and two together. I''m looking to pick up a pacnor hand lapped polygonal rifled barrel blank so I can turn down a custom barrel for this rifle and squeeze out as much accuracy as possible. tomorrow I'm going to tinker with the handguard so I'll post pics then
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    One of the best build threads I've ever seen. Really looking forward to seeing the rest.
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  11. #11
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    Not much to really type out here except painted and assembled

    Some late night final shots of the rifle in it's final scheme and fully assembled. I call this my sand shark skin paint job. It's very subtle and from a few feet away you almost cannot make out the pattern. I airbrushed this rifle using duracoat paints using a coyote brown base with an airforce digital tan top coat. Minor areas as seen left in black. When I bought the rifle from Jon it came with a little barska red dot "acog" which I also painted to match the rifle for now.

    I did make a minor modification to the handguard, and drilled a chamfered vent patter into the sides. Adds a little bit of extra grip as well.
    There were a few HK vented variants available but I didn't like any of them, so went this route. I've got a few more plans for this including a new polygonal rifled barrel, but those won't be fore some time as there is a bit of a waiting period before I'll have the parts available to even begin the work. So for now I'm going to just shoot the daylights out of it


    Hope you like it!







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    very nice!

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    Well done sir
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    Sweet ! I see what you mean by the shark skin paint job, very nice.

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    Sergeant RennFab's Avatar
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    Yeah it's a little bit lighter than I was expecting. Paints dry and they lighten up in shade but the coyote brown did so more than I expected. The vltor FDE as a base coat would have made it stand out much better but then I actually like the subtle tone of it now.

    Was windy as all hell up on my range today but I put 20 rounds through it none the less. Initial feel is good, trigger is much better. I have to get a second opinion from a GSG shooter(cough JVG!) but I think the recoil is a bit less as well, and I think this is mainly because of the slower bolt response due to increased spring pressure. Also want to get a better optic for this. While the red dot is cool and all, I think something with a better reticule and a little zoom would be nice for it
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