HKPRO Forums banner
1 - 14 of 14 Posts

·
Registered
Joined
·
81 Posts
Discussion Starter · #1 ·
I am looking to add a 3 lug barrel to my sp5k. I am going to pick up a can for it and thought about swapping the barrel myself. I've been a machinist for 20 some years and have all the tools to do the work including an 80 ton press. I know how to use a feeler gauge and all that.

Would this barrel work in the sp5k?

https://www.hkparts.net/shop/pc/MP5K-N-9mm-PDW-Threaded-Barrel-1-2-X-32-152p16968.htm

Do I reuse the trunnion or purchase a new one with it.

Are there any references out there showing how to fully strip the gun?

Will I need anything other than the barrel?

Thanks
 

·
Registered
Joined
·
8,464 Posts
Ok, so I'm a little bit wowed that you are going to try your first barrel swap on your SP5k, but it's your gun (and money). Some people might be surprised you are going to attempt this, while asking about the trunion, but that's them.

I can't answer all of your questions, but here goes (and I'm sure someone will correct me if I'm wrong or incomplete). You want to remove the lateral barrel pin that goes through the receiver/trunion. Failure to do so would be bad. Press out the barrel. Press in the new barrel from HK Parts. RIM or B&T, different options regarding quality/cost. Replace barrel pin. Likely you will have to drill a new channel for the pin. I would highly recommend that channel be the correct diameter, and if not, HK Parts sells over sized barrel pins. You will want to make sure headspace is correct. If you aren't sure how to go about correcting for head space, that's a whole different post. Good luck, oh, and don't forget about the front "triple tree."
 

·
Registered
Joined
·
81 Posts
Discussion Starter · #3 ·
Ok, so I'm a little bit wowed that you are going to try your first barrel swap on your SP5k, but it's your gun (and money). Some people might be surprised you are going to attempt this, while asking about the trunion, but that's them.

I can't answer all of your questions, but here goes (and I'm sure someone will correct me if I'm wrong or incomplete). You want to remove the lateral barrel pin that goes through the receiver/trunion. Failure to do so would be bad. Press out the barrel. Press in the new barrel from HK Parts. RCM or B&T, different options regarding quality/cost. Replace barrel pin. Likely you will have to drill a new channel for the pin. I would highly recommend that channel be the correct diameter, and if not, HK Parts sells over sized barrel pins. You will want to make sure headspace is correct. If you aren't sure how to go about correcting for head space, that's a whole different post. Good luck, oh, and don't forget about the front "triple tree."
Thanks for the reply. Thats why I posted the question here. There has to be a proper way to do this but it can't be impossible. I don't know the process for installing one but ai would like to try it. Thats how I got into the machine shop business.

Wouldn't the channel need to be milled for the barrel pin? Is that how you set the bolt gap and why the barrel doesn't come with the channel already in it?

If I find out the process goes beyond my tool and skill set I will send it off. I want to learn but not at the cost of my gun or safety.
 

·
Premium Member
Joined
·
3,871 Posts

·
Registered
Joined
·
81 Posts
Discussion Starter · #6 ·
I am not saying you cant do it but you should not learn on a brand new SP5K your asking questions that builders have paid for through trial/error/work/sweat/tears/years and you want someone to just tell you through a forum :rolleyes:

If it's that complicated I will find a shop to do it. I was not aware that much trial and error went into it. I assumed it had spec to follow and tolerance ranges. I do love to tinker but I'm not looking to ruin a 2000$ firearm to satisfy my own curiosity.
 

·
Registered
Joined
·
81 Posts
Discussion Starter · #7 ·
Doing a site search for 'install barrel' brought up some seemingly relevant stuff.

https://www.google.com/url?sa=t&sou...ggaMAA&usg=AFQjCNEmqxbb1ZcFagP2GXj8ksdDkY4b4w

And more....

Good luck to you.

BTW, are you sure you want 1/2x32 threads? If threaded at all, 1/2x28 seems more common these days.

RCM does not have a lot of info on the mobile site, might be worth a call.

MP5 BARREL PDW NAVY - Rim Country Manufacturing
I just used that link as a reference. I would go 1/2 28.
 

·
Registered
Joined
·
8,464 Posts
I just used that link as a reference. I would go 1/2 28.
HK makes their barrels with a narrow channel cut. I believe, once installed and head space checked, the full width channel is drilled and the pin installed. Often, when HK smiths install a used barrel into another gun (used barrel taken from a post sample weapon/parts kit), they rotate the barrel 1/3 so the lugs line up properly and drill an entirely new barrel pin channel.

Unless you already have a 1/2 X 28 suppressor, or plan to buy one (and not use a three lug mount which is by far the most prevalent mounting system for these barrels), then why not go with X 32 like a factory HK?
 

·
Registered
Joined
·
81 Posts
Discussion Starter · #9 ·
HK makes their barrels with a narrow channel cut. I believe, once installed and head space checked, the full width channel is drilled and the pin installed. Often, when HK smiths install a used barrel into another gun (used barrel taken from a post sample weapon/parts kit), they rotate the barrel 1/3 so the lugs line up properly and drill an entirely new barrel pin channel.

Unless you already have a 1/2 X 28 suppressor, or plan to buy one (and not use a three lug mount which is by far the most prevalent mounting system for these barrels), then why not go with X 32 like a factory HK?

I would use the 3 lug mount for the suppressor and the 1/2-28 would fit some compensators I would like to try out on it.
 

·
Premium Member
Joined
·
469 Posts
I am not saying you cant do it but you should not learn on a brand new SP5K your asking questions that builders have paid for through trial/error/work/sweat/tears/years and you want someone to just tell you through a forum :rolleyes:

There's info out there on many of forums to do many of things.. But why is it not ok with an Hk? Every builder your defending has gotten help along the way from another member or likewise. Some way have went for it, but info has helped a lot.
 

·
Premium Member
Joined
·
469 Posts
If you have a press, make a spacer using brass or a roll of pennies for the trunnion and something to space through the receiver.. Press it out wards. Line up new barrel if you have lugs... Press new barrel... Set gap to your desire.. Drill 5mm pin hole through original hole.. If it's off you will have to oversize pin.. If you don't have a end mill... Don't attempt to drill. Press new pin. Really the hardest of all this is de millling old tower , some just get a new sight tower, and pressing sling pin. Sight alignment can be a little tricky, make a sleeve out of aluminum or delrin on a lathe that fits Id of sight tower and cocking tube.
 

·
Registered
Joined
·
44 Posts
Is there an option to buy a barrel with the trunion already attached? I would like to add a 3 lug to my SP5K also and have been thinking about this option if possible.
 

·
Unrepentant HKHolic
Ones that go Bang
Joined
·
5,189 Posts
There's info out there on many of forums to do many of things.. But why is it not ok with an Hk? Every builder your defending has gotten help along the way from another member or likewise. Some way have went for it, but info has helped a lot.
I digress..........Good luck to the OP gleaning the info
 

·
Registered
Joined
·
81 Posts
Discussion Starter · #14 ·
I have decided to order a kit and attempt to assemble it and see how that goes before I start working on the real deal. It's to nice to start hacking up on my first go. These are not the same as slapping an AR together.
 
1 - 14 of 14 Posts
Top