Slippage on automatic sear axis pin (522)

[andrewgraw]

I'm having an issue with slippage on my automatic sear axis pin (part #522). Any idea what might be causing this? The rifle has been operating flawlessly, but the pin slips quite a bit during full auto fire. It's a registered receiver FNC with 3-round burst kit installed.

Any diagnosis or suggested fixes would be greatly appreciated. Thank you!

 

[dash]

Not uncommon to hear of. Stake it or mushroom the head slightly.

 

[navgunner]

I experienced the exact same issue with my RR. I staked one area of the receiver just beside the axis pin on each side. This was recommended and supervised by Curtis of S&H (we live close to each other).

 

[andrewgraw]

I experienced the exact same issue with my RR. I staked one area of the receiver just beside the axis pin on each side. This was recommended and supervised by Curtis of S&H (we live close to each other).

Thanks! Do you have a picture of what that looks like?

 

[navgunner]

Looks like my memory was a bit off. Sorry… I’ve been doing this for a while. The staking on the left and right we’re done by someone else and didn’t work. Curtis and I did the top and bottom. Looks horrible under magnification.

 

[andrewgraw]

View attachment 38700 Looks like my memory was a bit off. Sorry… I’ve been doing this for a while. The staking on the left and right we’re done by someone else and didn’t work. Curtis and I did the top and bottom. Looks horrible under magnification.

Thanks for the visual. This may be my best option.

If I could find the correct size, would you see any issue with using an anti-walk pin?

 

[navgunner]

Thanks for the visual. This may be my best option.

If I could find the correct size, would you see any issue with using an anti-walk pin?

Personally, I think that anti-walk pins would be a great idea, but I may get some flack on the boards because you could still allow rotation too (depending on how tight the pins are). Honestly, you’re going to do more damage if you let the pin walk outside one of the supporting walls of the lower receiver (while shooting) than you would from any rotation. This is my personal experience from a M16 (different firearm, but the principal is the same).

It may be worth you reaching out to KNS. The owner is a fantastic guy, and is very knowledgeable about machine guns, especially transferables of all types.

My logic about staking my FNC was more about “function over form” and despite the rarity of the FNC, I wasn’t disrupting the NFA registered component.

Your example looks superb, whereas mine doesn’t look as sharp despite having less than 1000 rounds through it. I chalk this up to the baked-on finish of the imported guns, the gloss finish weathers with age and handling over the decades. My opinion is the same with the IMI / Action Arms import UZI. Personally, I prefer the Cosmo soaked (greenish) look of the parkerized SMGs.

 

[andrewgraw]

Personally, I think that anti-walk pins would be a great idea, but I may get some flack on the boards because you could still allow rotation too (depending on how tight the pins are). Honestly, you’re going to do more damage if you let the pin walk outside one of the supporting walls of the lower receiver (while shooting) than you would from any rotation. This is my personal experience from a M16 (different firearm, but the principal is the same).

It may be worth you reaching out to KNS. The owner is a fantastic guy, and is very knowledgeable about machine guns, especially transferables of all types.

My logic about staking my FNC was more about “function over form” and despite the rarity of the FNC, I wasn’t disrupting the NFA registered component.

Your example looks superb, whereas mine doesn’t look as sharp despite having less than 1000 rounds through it. I chalk this up to the baked-on finish of the imported guns, the gloss finish weathers with age and handling over the decades. My opinion is the same with the IMI / Action Arms import UZI. Personally, I prefer the Cosmo soaked (greenish) look of the parkerized SMGs.

Thanks, really appreciate the candid feedback. This is my first FNC and first transferable, so I've been stocking up on parts and trying to learn the weapon inside and out. I'm going to talk to a couple of gunsmiths I trust around here for their opinion and reach out to KNS immediately to see what kind of solution they might offer. I strap a thermal on let this thing send it twice a year on pig hunts, so rotational erosion of the receiver isn't a big concern. I just want to make sure I keep it reliable for when I need it.

 

[paco]

In a normal FNC, the spring 525 is made so that it locks in the sear axis 522.
You might consider to use a clips like part 514 to lock the axis in place.
I only use the original sears.





Paco

 

[navgunner]

Thank you, @paco

Please explain the unique sear (middle pic, top FNC).

 

[andrewgraw]

In a normal FNC, the spring 525 is made so that it locks in the sear axis 522.
You might consider to use a clips like part 514 to lock the axis in place.
I only use the original sears.





Paco

Thanks Paco! Almost everything I know about the FNC is from reading your posts.

I’ll let you know what I figure out.

 

[paco]

Thank you, @paco

Please explain the unique sear (middle pic, top FNC).

The top one is a 1976 NATO Trial FNC, only made a few for these trials. Still has a AK47 type hammerspring. Note the bulge on the side. Later (1980) they changed the hammerspring to a helicoil type as you will have in your FNC sporter model.
Paco

 

[howdy]

I would definitely be in for a set of KNS anti-rotation if they decide to make some for the FNC. Interested to hear what solution you go with.

 

[andrewgraw]

I would definitely be in for a set of KNS anti-rotation if they decide to make some for the FNC. Interested to hear what solution you go with.

Talked to KNS. They don’t have anything that will fit, but they referred me to Halcyon Defense just down the road. Called them up and told them what I was looking for and the owner, Chad, said that the “FNC is the most underrated f**king rifle every made” and that he’d love to help make a custom pin. If it works out I’ll let you know. Driving up there in the next couple weeks.

 

[paco]

FNC is the most underrated f**king rifle every made

True...

 

[navgunner]

FNC is the most underrated f**king rifle every made

True...

Agreed.

 

[navgunner]

If the pins work out I’m down to buy too

 

[bauerdb2]

Loctite

 

[andrewgraw]

Update on this project: Halcyon should have it completed in the next few days. His idea was to mill a slightly longer hammer axis pin that will connect to the sear axis pin with a low profile link to create an anti-walk/rotation solution.

 

[andrewgraw]

Very excited to share the anti-walk/rotation pin set completed by Daniel at Halcyon Defense. Incredible work, he’s a true engineer. He milled new customized sear and hammer pins with grooved ends that seat into a modified KNS plate to create a low-profile and fully effective solution. Runs like a champ now.


All done in CAD and can be reproduced relatively easily, although there is some hand finishing work required.


He may run a small batch if there’s enough interest from our group here. Pricing will likely be in the $250-350 range depending on total units. This is his deal, happy to connect anyone directly.