A Tale of Two Sigs: Adding a Threaded Barrel to a P226 MK 25 and a Push-button Pivot Pin to a 556 SWAT 6

After considering a couple of upgrades for a while, I decided to add a threaded barrel to my Sig Sauer P226 MK 25 pistol and replace the forward pivot in in my Sig Sauer 556 SWAT with a push-button version for easier field stripping. Here’s a quick report on the upgrades.

I ordered all the necessary parts from Top Gun Supply, a well-respected online retailer of firearms and accessories. Here’s my order list:

  • KNS Push Button Pivot Sin – SIG 556 @ $19.95
  • Sig P226 Replacement Barrel – 9mm – Threaded @ $209.95
  • Barrel Thread Protector – M13.5 x 1LH @ $19.95

And while I was at it, I decided to order three Mec-Gar P226 9mm 20 round magazines @ $29.95 each (Mec-Gar is the OEM supplier for P226 magazines to Sig).

Here’s the pre-upgrade setup on both firearms:

Sig Sauer P226 MK 25 and 556 SWAT

Sig Sauer 556 SWAT KNS Push Pivot Pin Upgrade

I decided to do this upgrade because of the difficulty removing the stock front pivot pin in the Sig Sauer 55G SWAT lower assembly while field stripping. The rear pin works fine – press in from the side with a finger, slide the pin outward to a locked position, then pull down the entire lower assembly (which pivots on the front pivot pin). To completely separate the lower from the upper, however, the front pivot also needs to slide out. But there’s not as much recess around the front pin, making it harder (i.e. impossible) to push in with a finger. Additionally, the front pin is jammed in there tight – and required a hammer and a punch tool to dislodge from its locked position. On the later-model 556s (like mine), the pin itself is actually a sliding-locking pin, just like the rear pin. But because removing it requires tools, I wanted to swap in an aftermarket push-pin so I could remove the lower quickly and without tools.

After reading some other online reviews, I decided on the KNS Push Button Pivot Pin. After using tools to remove the front pin, I slid the KNS pin into place… but was unhappy with how the push-button portion of the pin sat in the assembly (the stock pin, spring, and retainer are shown removed):

KSN pivot pin installed in a Sig Sauer 556 SWAT

The push button didn’t stick out in the fully “up” position, making me worried that it might pull out unexpectedly at an inopportune moment. However, the pin did seem secure, but wiggled around in the factory holes slightly more than the stock pin. The final straw for me was how the bottom-end of the pin looks installed:

KNS pivot pin back side

It just looks too far from stock for me, and not in a good way, so I decided to go back to the original pin. Installing the spring and retainer required the use of one of the tools in my Otis Elite Cleaning System, and went a lot easier than I was expecting it to. I decided to try lubricating the front pin with some Tetra Gun, and after a few cycles of pushing in and out, I was able to get it so that it was easier to get out than before, but still not easy — and still requiring the use of a hammer. I’ll keep looking for a solution to this upgrade. To be fair, it’s possible that the KNS pivot pin works fine on earlier model 556s, but on my 556 SWAT, it’s a no-go.

Sig Sauer P226 MK 25 Threaded Barrel Upgrade

I love my Sig P226 MK 25 pistol. To quote Ferris Bueller, “It is so choice. If you have the means, I highly recommend picking one up.” The only upgrade I could imagine wanting on this gun was a threaded barrel, so I ordered the parts from Top Gun Supply. The barrel itself is Sig Sauer branded, which is a plus to me.

If you know how to field strip a Sig P226 (which is a cakewalk), then you know how to replace the barrel. However, I like to clean and prep all gun components before putting them into service, particularly with something as crucial to the proper operation of a firearm as the barrel.

I like to “season” my firearms with Tetra Gun spray. Anyone who has cooked with a cast-iron skillet or Dutch oven knows that objects tend to stick less to metal surfaces that are properly seasoned. Tetra Gun contains a quick-evaporating solvent and a fluoropolymer lubricant that is absorbed into metal to make it more “slippery,” just like cooking oil is used on cast-iron cookware. After a few post-cleaning seasonings with Tetra Gun, my firearms are much easier to keep clean, because the dirt doesn’t like to stick to them.

To start, I sprayed a liberal amount of Tetra Gun on the entire exterior of the barrel, and worked it into the metal with my fingers. Next, I sprayed some Tetra Gun on a patch and ran it through the new barrel:

First pass with a patch on a new P226 threaded barrel

Hmm… not quite as clean as I would have hoped a new barrel would be, but at least it justified the effort I was expending to clean it before installing it. I ran a solvent patch through, then a bore brush, and then another dry patch:

Patch after solvent and a bore brush

Wow – that was way dirtier than I thought. A couple more patch passes, and I was finally pulling a clean patch. I then soaked a patch with Tetra Gun, pulled it, let it soak in a while, and then pulled another clean patch. Finally, I wiped down the entire exterior of the barrel, rubbing in and/or removing any wet or shiny-looking spots where the Tetra Gun wasn’t absorbed into the metal (on Glocks and Sigs, I don’t like wet/shiny spots).

Assembly was straightforward: install the barrel in the slide, replace the spring, install the slide, and engage the slide lock. The last step was to screw on the left-hand threaded end cap (which I also seasoned), and admire my handywork:

Sig Sauer P226 MK 25 with threaded barrel installed

Now I just need to finalize the paperwork for something to screw on to that threaded barrel!

  • Regarding your issues with the KNS pin, you are not the only one, I have read that the best replacement take down pins are from CO gun sales, no complains of looseness, rather the fit is perfect and sometimes better than OEM. Perfect timing as there is a group buy going on right now to get them at a discount, so if you jump in then we are almost there to get the first tier of discount for the best replacement take down pins I know of. In my case I am getting either 4 or 6 pairs. 1 pair for my 1st gen ER/M4 style 556, where the front pins take two screw drivers (or dimes as the manual states) to unscrew the pin from both sides at the same time, totally sucks. My rear pin has become loose to where it easily falls out, and while I could fix it, I would rather replace it with one of these pins as I can completely remove it and that makes cleaning easier, and I want them to match cos of my OCD :). 2nd set is for my new 556R(ussian), which I bought brand new, so basically it doesn’t need them (yet), front pin is indeed tight as heck but I figure I can work it out over time, and rear capture pins is fine, but again, I like to get while the gettin is cheap. 3rd pair is for that 522 assuming I can confirm that the takedown pins are the same as for the 556’s. Given the 522 had some corners cut to hit its price point, I am assuming that the pins could use upgrading to improve the upper to lower “tightness”.

    Here is the group buy thread, it just kicked off like a week ago and they are still gathering buyers.


    • Thanks, Mike. I checked the link in your second comment, but wasn’t sure if it will fit on the newer 556 variants. The page simply says: “These are meant to replace the double screw on all original style SIG Sauer 556.” The KNS pin actually seemed a bit too short, which is why I think the button didn’t extend up all the way when installed (while the button worked fine when not installed). I’ll jump in on that group buy if I can confirm that they’ll fit and operate properly in the later-model 556. Does anyone on that forum thread know if they will?

  • I have read of several on the sig556forums that have used these pins to replace their TD pins in their second gen 556’s with good results. Regardless, to make sure that is supported (so that you can swap return the pins with no penalty if they don’t work), I just emailed them to ask, I will post their response here for posterity.

  • Mike

    I want to add a threaded barrel to my MK 25 also, but have always been told it needs to be “professionally fitted” to the gun by a gunsmith? I want a genuine Sig Sauer barrel, and preferably the phosphate coated one, although I am having a tough time finding one.
    What did you do about the “fitting” aspect of the barrel install?

    • If you get a genuine Sig barrel, it will just plop in without any special fitting requirements.