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New Clone build - Progress and Questions! Secrets and Answers.

8K views 41 replies 9 participants last post by  Discogodfather 
The MP5k uses a different bolt carrier (which is shorter) and the cocking handle is also about .75" back from where it would be on a regular MP5. SW made these flats so you didn't have to buy the very expensive factory style cocking tube (which is built like any HK cocking tube with the detent integrated into the tube not the receiver). Todd's idea was that you could then find a G3 tube and cut it down and then butt weld it to his flat. He also made this awful plastic cocking rod that came with the kit.

One option is to just cut out the part of the receiver (literally cut away the cocking handle recessed area about .75" from the edge) and then just weld in an actual MP5k tube. This is what I would recommend, the tube is expensive but it will work. The other route is to get a G3 stub tube (which is cheap) and cut and grind that up into something that might work.

I used the LSC Mp5k flat which required the cutout and then welded the factory tube in. It's difficult and you can see by my welds that it challenged me, lol. Great rifle though and it has not failed on me in thousands of rounds.


 

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Nice progress, but the image links are not coming up for me (seems like a photobucket maintenance thing, I will check back). Sounds like the exact same issues I had, the cocking tube is a tight fit against the trunnion and has a tendency to want to tilt upward. I can't say I solved that problem because my cocking tube is tilted upward a bit, maybe a degree. Maybe sanding down some of the material and more tack welding would have made it more straight. I also had a tough time fitting the cocking rod, this has been the case with many other HK builds I have. I ended up making an aluminum rod that goes into the cocking tube and presses against the inside of the receiver to act as a guide and a heat sink for running the weld bead. That has helped alot.

A trick I also use for better fitment is to get a very long drill bit (maybe a .375" 10" bit) and wrap some sandpaper on the end (I use the adhesive backed sandpaper) and then wrap it until you get a nominal diameter, then put it on a power drill and use it like a lapping device to help smooth the transition from receiver to cocking tube and eliminate and burs, weld slag, etc. on the inside.
 
This is a great tool to have in the box- a simple aluminum rod that is tuned to the cocking piece diameter and the receiver diameter. It acts like a heat sink during welding and also aligns the tube perfectly the the inside diameter of the receiver. I lived without this one on the few builds and can't remember why I didn't male one sooner, it makes life much easier. I made this one for a tight fit, I have to hammer it a bit to get it in and out.


 
The tabs and insert at the top are really nothing special but I was able to find them in a kit, so no fabrication. Very easy to make the top insert to factory spec on a lathe, it's basically just a stepped insert that protrudes about 1/16
" outward on each side. The tabs for the rear of the receiver are fine in 16 or even 18 gauge. They are structurally important because any stock that fits inside the receiver is going to put a lot of outward pressure and deform it without the tabs (with a ton of force). If you need exact dimensions let me know.
 
On an MP5 cocking tube length is not particularly critical as there is no lockout claw in the mechanism. If you compare it to a G3 or a 33, there is no "lever" just a stub with a little ball detent to keep it from flapping about too much. The problem is not going too big of a gap but too small. If the carrier is at all impeaded and there is no clearance to the coking tube the action will not fully go into battery, and you will also get false bolt gap readings. Most people don't want a big 1/8" gap either because it feels too loose. I try to go for a minimal gap of around .020-.030" but some say .050-.060". Again, like most rollerlock problems, this one will not effect the gun cycling and seeming to work.

If you get stuck in a build where there is not enough of a gap then you can turn the coking tube down a bit to get the right gap. If you went too loose and you need to make up some space then you can always weld in a section, but bear in mind that this is a hardened part and you are going to anneal it. This could lead to wear problems down the road.
 
I just do it straight up, no need to get too artistic. Initials, number, where it was made, and I like putting the 922r compliant line on there. I think it has value.

Problem with putting HK logos on things is that people think it's somehow from Oberndorf and that adds value. The problem is not with the builder because most of us will freely declare where it's actually from. The problem comes when you sell/get rid of it and unscrupulous dealers try and pass it off.

Some things I encountered with regards to engraving: There are very few people left who can do a good job with a pantograph or even chemical etching process. 99% of the people and companies that will do it are using a fiber laser, which is a special kind of C02 laser that has a very limited travel and is usually much more expensive than a regular laser. This means that very long lines or lines that are engraved on different surface depths add lots of cost to the process. They generally really like it to when they have the ability to engrave the flat pre-bending. It makes it much easier for them to set it up and there are no firearms or FFL issues to deal with.

They produce the best work when you give them a vector based graphics file with all fonts converted to outlines. AI files, DXF, DWG, etc. If you give them a drawing or a picture it adds costs as they have to convert to vector information.

Avoid at all costs the electric punch style engravers, even the CNC ones, they look awful. I was very surprised to see my latest PTR receiver acquisition had the serial number stamped in this way on the top rib, yuck. I like to a void the top rib for engraving (even though this is factory style) because everything you can think of tends to obscure it. Like welding a pic rail, or just using a bolt on extended rail, etc.

 
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