HK G3A4 build part 1,2,3,4

[switchpod (AJ)]

Part 2!
Part 2 may seem boring, but is essential to your build. Checking the head space!
Take your bolt/ carrier assembly and barrel and trunnion, insert your go gauge and lock in the rollers into the trunnion. Now measure with feeler gauge to measure the space between the back of the bolt head and the front of the carrier.

For clarity sake I don’t have the bolt in The trunnion, but you can see from the picture that this one measures out at .007” of head space. The spec for a HK G3 is .004-.020 if you are getting a larger measurement or smaller you can buy smaller or larger diameter rollers and install them into the bolt head.

For this build you can buy a flat receiver and tooling to bend it into its shape. The problem with doing that “at the time of this and in my location” you can never sell or give some one this firearm or receiver. In the end you will have to 1. Submit it to the BATFE, or destroy it with 3 torch cuts. They even need to be a certain width of cut.
Because of this I opted to use a PTR for a few reasons.

1. @ThisOldGun recommend it.
2. This is a firearm and a S/N. So you have a FFL transfer so in the future I can sell, or hand it down to my kid!
3. PTR bought HK machines for all their builds so for all intents and purposes it’s a HK receiver built by PTR.
4. They have a pica tinny rail already welded on them, rear sight base, rear pin reinforcement plate, and the full auto blocking shelf welded in already.
5. This way I avoid buying expensive bending jigs that I most likely will not use again.
   
   
   
   
   
   
   
   Next de-bur all of your edges to make them less sharp. Also break the edges on the full-auto blocking shelf (those can get very sharp).
   
   
   
   
   
   
   You can now plot out where you are going to drill the holes for your spot welds on the trunnion and charge tube. Mine are 1/8” so I just used a 1/8th drill bit.
   
   
   
   
   
   
   Now carefully insert your trunnion and see where the scratches are. Lightly sand with 200 grit or higher. Scotchbright works as well to make the parts fit better.
   
   
   
   
   You can also use a file, lightly if needed.
   
   
   
   
   
   Continue to fit and sand as needed until both the trunnion and charge tube makes contact with the receiver stop.
   
   
   
   
   Install the rest of your parts to check for fit. Make sure you are happy with how everything fits, it’s easier to do this now rather than later when you have the metal parked, painted, or blued.
   Remember Be safe and have fun!

[Robert]

Look at all that awesomeness !!!

[Mosinvirus]

Loving it!!!

[ThisOldGun (Rusty Shackelford)]

Nice!!!

[switchpod (AJ)]

Part 3!
It’s that time to make everyone cringe and turn the full auto bolt carrier in to a semi-auto carrier..
This is a full auto trigger assembly and none of this I’m using on my build. I ordered a “navy” PTR trigger group that counts as 5 points to the magic number 7 that I’m looking for to stay 922r compliant. The other two points are the receiver and the flash hider.

Here is the lever that lets the hammer drop in full auto mode.

And here is what it interacts with to know when the carrier is closed and ready to fire. We are going to have to cut this out. You can use a file, dremel, mill whatever you have at your disposal!

I opted to use the mill with a 3/16 full carbide 4flute end mill. It worked like a charm at 2,000 rpms.

When your done don’t forget to treat the metal. And oil it.

Remember be safe and have fun!

[switchpod (AJ)]

Part 4!
It’s time for small parts fitting. And if you want to install a paddle magazine release.

Make sure you have all your parts. In this picture the detent ball for the rear sight is already installed.

Make sure everything fits.

Remember fitting your parts is not fun and takes a long time if you want a perfect fit so take a break every few hour or so.

If your interested in a paddle release you can get a kit of stainless steel bushing and pin, or you can make one.

The pin measures 1.000” long by .125”. The the bushing measures .610” long, small diameter is .295” bigger diameter is .375”, only .055” long of the total .610” length is for the larger diameter. The through hole will be .127”

The pins are both oversized so you will need to trim both of them down to fit.
Mine was .5875” to fit.

Install your contact piece first and then your compression spring, magazine catch, and push button. Make sure everything fits and moves freely.

The full auto block will get in the way of the paddle so you will have to remove some metal on the inside of the receiver.

Go nice and slow cutting a little at a time.

Once that is removed you can start measuring where to drill a blind hole.

Move the receiver to the left side. Note the center of the magazine release hole and measure .610 below center and make your scribe lines. You can use a square for staying straight left-right.

Use a 1/8th drill bit “.125”. Remember do not drill all the way through the far side, just enough to support that end of the pin.

Now install the pin, bushing, and paddle.

See how everything works and use a magazine. You may have to remove some metal so the paddle has clearance. Note if you take to much metal the paddle will rattle. The metal on the receiver will have a bit of pre tension and that is what you want. Once everything works the way you want your done!

Now once everything works good cut the pin flush so you can weld it in later.
Remember be safe and have fun!

[Mosinvirus]

Awesome!

[Chance (Zach)]

Excellent write up!

[Robert]

bla bla bla

[switchpod (AJ)]

Sorry guys. I have been extremely busy as of late.
Every build you do you should always have a personal touch that makes it fun for you. I don’t do my builds to be 100% original looking. My goal is to have fun not trick anyone into thinking a build is original. With that said I looked into stampings that the G3 would have.
With my current time restrictions I had to make it quick on this little accent.

So this is what I came up with.

I used a 40 degree bit for the engraving.
Remember it’s your build have fun with it. Make it your creation!
Be safe and have fun.

[LonewolfMcQuade]

Awesome!!

[Robert]

GORGEOUS!!!

small words so its not unclear to the software

[Merlin7 (Robert Zoerb :mage::zap::us:)]

WOW I am so impressed with the presentation and layout. I feel as though I am right there sweating with you. The attention you provide to correctly fit and finish the stages to function properly but also there is the reminder that there is an element of fun and accomplishment to be gained. Do you keep the work area in your shop always so neat and tidy? I really enjoyed watching your project, thanks!

[switchpod (AJ)]

Thank you. I do the best I can with what I have. I keep the areas as clean as I can with in reason. I have been extremely busy and had to get a refill of Argon gas for welding, so in the next few weeks hopefully I can get some more posts up.

[Merlin7 (Robert Zoerb :mage::zap::us:)]

Good, look forward to more of your posts.

[switchpod (AJ)]

Supplement;
Finally able to be in the garage for a few hours, and I noticed that I didn’t like the way the receiver was looking on the auto blocking ledge.

It just didn’t look good to me. I got out the welder and started filling in some areas.

Grinding and filing away.

Not done yet but getting close.

[SAK]

switchpod, you got serious skills, excellent work!

[Robert]

more better

[Mosinvirus]

As someone who currently can only take material away I envy everyone who can also add material…

Well done!

[Merlin7 (Robert Zoerb :mage::zap::us:)]

Once again, you are providing pretty good training aides. I appreciate your take on HK products.