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Thread: MSG90A2 build- Cetme Build Tutorial

  1. #1
    Veteran dirty8's Avatar
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    MSG90A2 build- Cetme Build Tutorial

    I usually post on the HK Pro board but I'd like to share a recent build.

    I was asked to assist with a custom MSG90 project. The barrel is a JLD 20" barrel. A BMP trunion was utilized. The gun has no iron sights. Instead a Picatinny rail and front sight base was added. Let's get building.

    I went ahead and dremeled out the magazine flapper pocket with a carbide bit.


    By dirtyeight




    By using a clipped/pinned lower, I was able to determine where to drill for the paddle magazine bushing pin. The pin is a 1/8" dowel pin. 3/4" or 1" will work. You will need to trim the 1" pin before welding. I use an undersized bushing. The will give a loose fit, but when assembled with the rest of the parts, will feel very smooth. There will be no binding or break in period required. No need to sit at the TV and moving the paddle back and forth a thousand times.



    By dirtyeight




    I went ahead and pilot drilled the pin hole with an undersized drill. I finished reaming out the hole with a 1/8" carbide end mill.



    By dirtyeight




    I went ahead and squared up the bottom of the paddle pocket with an end mill.


    By dirtyeight



    Here's a pic of the pin hole ready to be welded. I went ahead and set the TIG welder to 35 amps max. My TIG has a foot pedal control for variable heat setting. Anyone considering picking up a TIG should seriously consider an adjustable unit.



    By dirtyeight



    By dirtyeight



    After the weld cooled down, I placed the receiver back on the mill and machined the area to clean up the weld. I went ahead and abrasive blasted the shelf area.



    By dirtyeight



    I went ahead and placed the receiver aside and worked on the barrel/trunion. The barrel diameter is checked as well as the trunion. The interference fit should not be greater than .003-.006. If the diameter is too thick, the barrel will gall. A little oil/grease will help the barrel seat smoothly.



    By dirtyeight



    After the correct bolt gap is achieved, I went ahead and pilot drilled the trunion and reamed it out the a 5mm reamer.




    By dirtyeight




    By dirtyeight



    I went ahead and milled out a piece of Picatinny stock to fit on top of the cocking tube. I wanted the front sight base to sit on top of the cocking tube with the correct profile rather than looking like a chunk of metal just welded on as an afterthought.



    By dirtyeight




    By dirtyeight




    By dirtyeight




    By dirtyeight



    Okay enough with the front sight base pics. I took down the ejection port ledge with a dremel in preperation for the forward assist.



    By dirtyeight



    I placed the receiver into the mill and cut the slot for the forward assist pawl.




    By dirtyeight




    By dirtyeight



    Okay, time to do some welding. I went ahead and placed the barrel trunion into the receiver as well as the converted coking tube. I went ahead and placed a brass heatsink into the cocking tube and made sure the tube was aligned correctly. The MSG90/PSG1 handguard is fitted to make sure the locking mechanism will lock into place. The TIG was set to 35 amps max.



    By dirtyeight



    I went ahead and turned the amps back up to 85 amps max to weld the trunion into place. The spot welds were left slight under filled to simulate the factory spot welds. The welds near the channels were left under welded also to allow the T rails to fit.



    By dirtyeight



    The hardest part of the build was to weld the T rails into place without warping the receiver and have a decent looking weld. The T rails are fairly thin and requires alot of patience. Unfortunately I don't have a dedicated welding table where I can sit down and have a solid welding platform. The TIG was set to 30 amps max. I went ahead and used a felt pin to mark the length of weld for each seam. I use an aluminum heatsink to keep the receiver straight and prevent burn through.



    By dirtyeight




    By dirtyeight



    I went ahead and dressed the welds down and reblasted the receiver.



    By dirtyeight




    By dirtyeight



    I used a dremel tool to follow the contour of the T rail on the ejection port. I lowered the ejection port make the rail look as if it was blended into the receiver.



    By dirtyeight



    I attached the forward assist housing to the receiver with the use of steel wire. This is a good way to keep the parts in place especially with odd shaped parts.



    By dirtyeight



    I went ahead and welded the housing into place with the heat setting at 35 amps max.




    By dirtyeight



    The next part to be installed was the Picatinny rail. This is my modified rail which allows the serial numbers to be visible.



    By dirtyeight



    The TIG is set at 50 amps max and spot welded into place. The receiver is again blasted.



    By dirtyeight



    The front sight base is welded onto the cocking tube. The heat setting was set at 30 amps max.



    By dirtyeight



    The chamber and muzzle gets plugged and the receiver goes back into the blast cabinet. After every nook and cranny is blasted the receiver is cleaned, rinsed, and given a bath in Maganese Phosphate (big fancy word for parkerizing).



    By dirtyeight


    The gun is removed from the park tank, neutralized with water/baking soda solution, and scrubbed with my wife's toothbrush (An old one of course. I'm sure a tooth brush with some aluminum oxide residue would work better than Arm and Hammer tooth paste with baking soda, LOL). The receiver is given an air blast with the air compressor to remove any traces of water. The receiver is placed into an oven and set to 250 degrees to make sure all moisture is removed. The gun is now completely bone dry.



    By dirtyeight



    I let the temperature drop back down to about 120 degrees and remove the gun from the oven. I use a mixture of 3:1 ratio of Gunkote flat black to semi gloss black (3 parts flat to 1 part semi gloss). I apply the paint while the gun is still warm.



    By dirtyeight



    The gun is allowed to sit overnight before final baking at 325 degrees for an hour or so.




    By dirtyeight



    After the gun is refinished, I filled in the stamped lettering with Brownells Laquer Stik. Rub the stick on the lettering in all directions to make sure the lettering gets filled in. Use a towel with a light coat of CLP to clean up the excess paint. Do not push too hard or the towel with go down into the lettering and you'll have to start over.



    By dirtyeight




    By dirtyeight



    After the gun is reassembled, the bolt carrier, interior receiver, mag catch parts, and cocking tube gets a light coat of CLP. The bolt drops in with no problem. The cocking handle unlocks correctly, no binding as well as the paddle magazine release.


    Here's a few pics of the final product. Take care! JFK out.




    By dirtyeight




    By dirtyeight




    By dirtyeight




    By dirtyeight

  2. #2
    Senior Veteran Buelligan's Avatar
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    DIRTY8, That is some SWEET work. We need a range report.
    JOHN 3:3 C.O.G#170

  3. #3
    Veteran lakeracer69's Avatar
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    Dirty Eight,

    Where did you get the picatinny rail stock from?

  4. #4
    Senior Veteran turbothis's Avatar
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    very nice.
    have cnc mills, will work for food.
    http://www.gunsnorthwest.com/

  5. #5
    Planning's Avatar
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    great work, thanks for showing how it's done.

  6. #6
    Veteran JayGeeWentWorth's Avatar
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    Thumbs up

    Another excellent build and your picture intensive, detailed writeup is great. Thanks for posting this here.

    Also, what made you decide to go with the magpul stock as opposed to a true MSG-90 stock?

  7. #7
    Veteran dirty8's Avatar
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    Just to answer a few questions, I did this build for a friend who pops in from time to time. He wanted the Magpul stock because it fits his needs. I have another build that I did earlier this year.

    I'll take some pics of both guns before he comes by. I machined the Picatinny rail to fit the receiver. It takes some time to machine the metal down to fit the top of the receiver.

    My last build (hopefully some time this year) will be another MSG90, which will include a factory scope mount. Hopefully it will look close to the factory model (no iron sights, just optics).
    Last edited by dirty8; 08-01-2008 at 09:49 AM.

  8. #8
    Senior Veteran Woodman in MO's Avatar
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    Wow, that looks awesome. Great write up. If I may, why put on a forward assist, did you have to notch the bolt down or was that already done?
    "When shoes and clothes and food, when even hope is gone, we'll have the rifle."

  9. #9
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    my word that is SO COOL!!!
    "For every minute, the future is becoming the past."
    -Thor Heyerdahl

  10. #10
    Veteran Stillife's Avatar
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    Wow really professional work! I also want to know where you got that picatinny rail stock from.

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