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Discussion Starter #1 (Edited)
Hi all,

Looking for a DIY method to 'permanently' install a barrel extension on my MP5k (threaded with three lug). I also want to be able to 'uninstall' it myself.
Firearm originally a pistol, so I am looking to temporarily convert it to rifle, and then later on be able to take it back to pistol. While I doubt anyone would ever challenge the permanence of the barrel extension, things happen, and I'd like to be able to utilize a method that qualifies as permanent (or whatever the ATF requirement is), and be able to undo it later on without any permanent marks or damage.

What's out there? Also, where are people getting barrel extensions from (fake suppressor, other options)?

I also have some items I want to sell and I cannot yet (I assume low post count), so this is hopefully going towards that!

*edit*

Just found
http://www.hkparts.net/shop/pc/viewPrd.asp?idproduct=1942&idaffiliate=7

Seems expensive for a temporary solution. I am sure it looks nice though. Blind pin = just drill it out (carefully, say with a drill press) afterwards?

*been doing a lot of reading*. Looked at Silver Solder (1100F) too... eh. I would think thread, pin, and just spot weld over it would be the easiest to 'undo' later on... So any reasonable shrouds/fake cans that are longer than 8''? Mp5k barrel is only what, 5.5''? So need something longer to reach the 16''...
 

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I like the barrel extension that jayson at IGF sells. I'm not sure if his web site lists them but i asked him about it. it clamps onto the 3 lugs and then you can drill insert a pin and spot weld over that.
 

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Discussion Starter #3
I'll take a look at that. I still cannot find (even at hkparts.net) a barrel extension that works with mp5k! Heck, it's threaded 1/2 x 28, and 3 lug, and I cannot find one anywhere that is long enough. hkparts has the 8inch urbach, but 8'' + 5.5 (I think that's mp5k, if not 4.5, not counting the threaded extension I had done by S&H arms)... So what is one to do?
 

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The MP5K-PDW barrel will be too short for most extensions as they are typically 8" long to go on an 8.9" standard barrel. You will need to have an extension specifically for the 5.5" PDW barrel.

The IGF ones, while plain looking, mount in a manner that you can blind pin it without having to drill into the muzzle. I would check with Jayson as he can probably custom make you one for a PDW length barrel. Also keep in mind that the MP5K receiver is shorter so you havbe to make sure not only to get the barrel over 16", but long enough to get the OAL over 26" with the stock folded.
 

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OP might be in a NFA not-kosher state, like WA state where I live.

SBR = no go with state law.

Wish it was different, I would have an MP5 SBR and MP5K SBR.

Instead I roll the 34 to be legal and all that good stuff.
 

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Discussion Starter #8
Nah. Looking at IGF's prices, I might as well SBR the stupid thing. =) Also, the measurement is with the stock FOLDED. And yes you can go pistol to rifle to pistol. I appreciate those posting accurate information (or correcting others, or me). I am an in SBR state, but I mean, I am at 6months right now (should be here any day now). Only thing is I might move to a non-sbr friendly state and need to make/keep it a rifle. oy.

Can I make my own barrel extension/shroud as long as I affix it legally (1100 silver solder, blind pin, weld, etc)? Toying with that idea.
 

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Discussion Starter #9 (Edited)
I figured it out. Remember that new interpretation from the ATF? If the overall length is greater than 26'', and the barrel is less than 16'', and the item has a vertical fore-grip (which an MP5k should), it is now just a 'firearm', and not an AOW, nor an SBR. Stock measured open/how it is intended to be shot.

So, two options

1) Add a big spacer on the end of the stock until the stamp comes back
2) Add one of those 8'' Urbach or similar extension (pin/weld... is that required, as we are NOT making it into a rifle permanently, but a good idea I suppose?) and it will meet the requirement (length) above.

For both, you *need* the vfg, ha.

*edit*
Lol I'm a little slow today... I think one of the requirements is NOT mounting a stock... ha. I was trying think 'any why isn't this an SBR by definition'. doy. Ignore.

So I basically need to buy a tap and TAT and thread a long pipe, blind pin and/or weld, and file my SBR paperwork. Looks like that's the best way.
 

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if you could find some sort of 3 lug attachment that actually rotates onto the lugs to lock. then blind pin in a way that prevents unlock rotation, rather than pinning into the actual lug, there would be no permanent holes drilled into the lug/host, and it should meet the requirement for being permanent.

I am not a lawyer, so the 'should meet the requirement' should not be taken as a good to go.

ETA:
if I remember right, the length that a k gun barrel has to be extended to remain legal for the OAL requirement is 19"
 

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Also could make a washer shaped like the opening of the 3 lug extension, put it on first then after installing the fake can weld it to the back of the can covering the cutouts/openings that allow it to slip on/off the lugs.

 

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The mp5k extension that jayson sells (~80$) is roughly 11.5" long so that brings the barrel length up to 16". But about being the minimum required length OAL I'm not sure. If you put one of those fixed stock adapters that would work. But if it is a folding stock and you measure from the folded position (or just back plate) then it would bring you to about 24", so I think no go.
 

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Why are you measuring from folded? OAL for SBR determination is done from extended, with the exception of some states, like CA, yes?
 

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Buy two extensions. Then, cut and weld them to the proper length. Doesn't seem that difficult. Probably going to look pretty ugly. :wink:
 

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I extended mine in the time I was waiting form my stamp. It is threaded 1/2-28 and fit over the three lug. You blind pin behind the lugs and it's not able to unscrew. No damage to barrel. However it would foul up and become inaccurate. I still have it if you are interested.
 
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