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Discussion Starter · #1 ·
Does any one have experience making one of these? I have pestered a few of the vendor/builders here to see if any of them had a spare they would be willing to sell me. No luck. Hkparts has a listing but they are out of stock and I don't know how long ago they had them or if this type of build is still popular. Being from Ca with no possibility of an sbr this type of build makes sense to me. So the next step is to make one. The questions I have are:

Are they all the same diameter between the different calibers, could I splice a 9mm with a 5.56 or 7.62 to get the length I need?

Does the support piece stop against the inside of the tube?

What is the OAL of a 93 tube?

I will probably have more questions but this is a start.

Thanks for looking!
 

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They are a pain to make, but it's all possible if you want to use the 33 forearms. You take a MP5 tube and cut it, then weld in a piece of sectional stock from a donor tube. HK parts sells the actual tube section stock. Yes they are all the same diameters across calibers.

https://www.hkparts.net/shop/pc/Cocking-Tube-Extrusion-12-Section-9p13487.htm

Cut the MP5 tube close to the transition where it goes to the finned tube. Measure a section of the donor finned tube and weld the whole thing together. The hard part is getting all those little fins to look decent, unless you want a weld bead running through it which makes it look a little hacked together. There is no support piece on the inside of an MP5 tube, if I understand that question correctly.

Let me measure the 33 tube length when I get a chance, just have to pull it out of the safe.

FYI HK never made these.
 

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Discussion Starter · #3 ·
Thanks for the link, I did order that piece of tube in the link. The support I'm talking about is the piece that the charging handle attaches to that rides inside the tube.

FYI HK never made these.
I know but I'm in Ca and we'll never get to sbr anything. I think a little extra sight radius would be a little more practical than a fake suppressor, especially with aging eyes.

Thanks
 

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I have never messed with the actual MP5 40/10 style cocking pieces, they are a bit different. The project I did work on just used an MP5 cocking piece. It worked fine but it did not have any recess to lock into, so the handle flopped around a bit in there. I remember having the idea of taking an end of another cocking tube, the "small end" and cutting off a section of it and welding it into the area where the ball detent could lock into, but I never got around to it. I think it would work fine, you'd have to plan to have that little 1" small end ready to weld in right after you cut the MP5 tube.
 

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Does any one have experience making one of these?
Yeah, I've machined a few cocking tubes from 4130 tubing or solid round stock before; as mentioned above it would probably be easier for the average builder to just use the blank extrusion that HKParts sells, slot with a dremel, and trim it to fit.
The MP5 doesn't require hardly any force to unlock the rollers, so it really doesn't have to be a terribly involved or closely-machined-to-tolerance part.
 

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My hk33 tube measures 250mm from the point of contact to the receiver (welded area) to the end. I think it's always a good idea to put the tube on the receiver and mock it up with the forend in place before welding the hanger for fine adjustments.
 

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Discussion Starter · #7 ·
Thanks for the help I got the stuff on the way from HK Parts. We'll see how it goes. 250mm, they give you a 12" piece. You could actually make a complete one from that also taking into account the part that fit into the receiver.
 

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I am building a couple using the extrusion material from HKparts and the demilled end off a G3 from RTGparts. Turn the od down on one end and add a 23mm doubler and turn the id back some on the other to insert the G3 end.
 

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Easiest way used to be to use an HK33 tube, which is already the right length, and weld in an insert that 'he who shall not be named here' sold that reduced the length and had the groove for the ball detent to go into.
 

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Easiest way used to be to use an HK33 tube, which is already the right length, and weld in an insert that 'he who shall not be named here' sold that reduced the length and had the groove for the ball detent to go into.
The problem with this is you have a slot that is now too long, a cam action surface in the wrong place (un-needed) and the handle locking pin hanging out on the side with nothing to do. Also the support detent ring will either show through the slot or not be in the right place due to the other cam surface in the tube. YMMV
 

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Discussion Starter · #11 ·
The 34 tubes are back in stock and thats what I used. I now have the bulk tube, mp5tube and G3 end for the parts bin. I was running out of time and would still need to find someone to weld it.
 
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