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