I finally got to pick up one of my dream guns: a brand new HK SP5K-PDW (while the MP5k version would have been preferable, I still have a mortgage and 2 kids at home). I at least partially blame arcwelder for pushing me over the edge on this one.

I immediately put in an eForm 1 to be able to add the requisite foregrip and collapsible stock. While that turned into a 159-day saga of its own (see the NFA wait times thread!), I had a more immediate issue: the 9mm YHM Cobra-9 can I've used on my West German P226 would not fit this new gun!

The SP5K-PDW comes with the typical tri-lug on the barrel, but it also has threads. Unfortunately for me, they were 1/2x28 while the Cobra-9 had 13.5x1LH thread to fit the SIG! I called up Yankee Hill to see if they still sold pistons/adapters for that can. Nope; they were all discontinued long ago.

Well...shit.

Since I recently stood up a lathe and milling machine in my garage, I decided to get creative.

First, I took a scrap piece of 1.5" diameter steel round stock. I turned it down in the lathe and bored a hole through it. Here is a photo next to the 13.5x1LH piston from the YHM can.



Next, I had to mill the lugs. Not bad, so far.



Do a little grinding and filing...



...and boring on the lathe...



It's fitting nicely so far.



Apply enough lube and TAP THAT.



You'll notice the pistol piston has a shoulder (the threads are recessed); it seats on the crown of the barrel. The one for the HK seats against the tri-lug, so no shoulder is needed, only a nice, square end.



Add some vent holes. In retrospect, this wasn't necessary at all since I was replacing the spring with a solid spacer. Oh well...it still came out nice.



I then used a torch to get it cherry red, then quenched it in mineral oil, followed by a tempering in the oven. All required? Maybe. I still felt productive.



The solid spacer after being turned on the lathe and heat treated.



Must...shoot...something.



However, I still knew better. I decided to check the alignment of the can with a suppressor alignment rod. I was happy:



I have a Dead Air Wolfman in NFA jail. It will go on with the tri-lug mount for a shorter package. It shoots VERY nicely with subsonic 147gr reloads with the 80 degree bolt locking piece (made for shooting suppressed 147gr, standard is a 100 degree locking piece). Muffs are for chumps!!

As soon as I got my Form 1 approved (today!!), I topped off the HK with a Midwest Industries handguard, MFI rail mount, Safety Harbor collapsible stock, a diopter rear sight drum, trigger pack upgraded by Bill Springfield, Trijicon SRO with Scalarworks mount, Viking SMG sling, vertical foregrip from A3 Tactical, and 4 factory German mags.

Now I just need to cut some foam...



With its bigger, slightly louder brother:

What! I was completely captivated by the thought of a YHM Cobra getting a facelift. I thought a trilug adapter was being made.
I have the same can--sits on my CZ Scorpion. Cobra 45 was sent to ECCO for a baffle upgrade (jail break).
Excellent job --well done.
I'm going to make one comment after looking at the photo with the YHM wrench. You could have machined a fixed mount replacing the piece the piston is contained in.

Nice work!!!

quote:

Originally posted by SIGfourme:
What! I was completely captivated by the thought of a YHM Cobra getting a facelift. I thought a trilug adapter was being made.
I have the same can--sits on my CZ Scorpion. Cobra 45 was sent to ECCO for a baffle upgrade (jail break).
Excellent job --well done.
I'm going to make one comment after looking at the photo with the YHM wrench. You could have machined a fixed mount replacing the piece the piston is contained in.

True, I did consider doing a trilug and fixed mount. I wasn’t patient enough and wanted to shoot it ASAP! Both of those options would have required a bit more planning than just trying to replicate the existing mount.

Thanks for the kind comments!

That's quality work, there. I'm impressed! That SP5 turned out great, too. Now get that sucker smoking!

I love this as someone who is also a garage machinist. And of course you will 100% want to get to trilug. And I love my wolfman on my HK. But why didn't you just make a very simple thread adapter? Seems like a way easier way to solve the problem temporarily?

quote:

Originally posted by hrcjon:
I love this as someone who is also a garage machinist. And of course you will 100% want to get to trilug. And I love my wolfman on my HK. But why didn't you just make a very simple thread adapter? Seems like a way easier way to solve the problem temporarily?

Because I could use the practice! Also, I didn't want to buy a 13.5x1LH tap that I would use one time. An adapter between the two threads also seems less secure than just making a new piston/spacer. Plus, that would have added more tolerances to throw off my alignment.

The tri-lug mount is in my safe...waiting for another absurdly long ATF wait.

This is awesome! I wish I had the skills and tooling to do that kind of work. Nicely done, sir!

I have a YHM Cobra and an SP5. My SP5 has been pretty good with the Cobra. I did pick up a Gemtech Lunar 9mm so I could use the three lug mount but I thought the Cobra was a little quieter.

YHM still has these in stock and i think it fits the Cobra, Cobra m2 and Sidewinder.

https://yhm.net/products/sidew...ect-thread-adapters/

quote:

Originally posted by gw3971:

YHM still has these in stock and i think it fits the Cobra, Cobra m2 and Sidewinder.

https://yhm.net/products/sidew...ect-thread-adapters/

Da hell…I called YHM, described what I had and what I wanted, and they said I was SOL as far as an adapter for my Cobra. Did these just come out? Maybe I got a dumbass on the phone or these won't fit a Cobra as old as mine. Either way, it was fun to make and I got at least one level up on my skills.

The new YHM Sidewinder now uses pistons compatible
with Dead Air, Rugged and SilencerCo.
Geez, I have to keep up to date with "old school" suppressors.
Again --great work with the lathe.