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Thread: Adjustment and Fitting new Cetme/HK receiver flat Questions.

  1. #1
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    Adjustment and Fitting new Cetme/HK receiver flat Questions.

    Hopefully I'm getting near the end of these questions. I am unable to upload photos from any of my devices for who knows why so you'll have to bear with my descriptions.

    Question 1. If I weld my receiver with the two halves touching which fits my trunnion perfectly my magwell opening is 1.07" wide but my mags all need around 1.15", do I weld it closed and just bugle out the magwell (sounds ugly) or put a .08 gap on the receiver and weld it shut over a carbon block while squeezeing it shut over the trunnion?

    Question 2. Similar to question 1 but more of an observation. With my semi auto shelf weldment slipped over the back of the magwell where it goes there's a .08" gap between the receiver halves, if I push the pieces together like everybody does in the tutorial videos the same gap will be instead around the weldment and the mags won't even come close to fitting, the grip frame fits when its open .08" so I assume I need to weld it with that gap but is that normal? Is this just a crappy flat or are these normal problems to run into on a build. If I had just folded it and welded it like I had seen done in some videos I'd be cutting them back apart.

    Question 3. This is a PTR brand receiver ( https://www.hkparts.net/shop/pc/Rece...R-234p2320.htm ), the magwell has a large ramp up at the front of the opening which holds the mags out about .2" from where they need to be, all the pictures I can find of finished rifles show this just cut straight with the normal lines. Is this for fine tuning mag engagement/depth or is this possibly just so I can cut off the part of my weld where it always creeps in at the end of a buttweld?

    Again thanks for the help and I hope you can all bear with me but as I said before I'd much rather ask stupid questions than be cutting this apart and redoing things. I really want to do this right and see a lot of knowledgeable people on here.
    I will show some of my build when I'm a little farther along (if I can figure out why it's not letting me upload pictures).

  2. #2
    holescreek's Avatar
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    I've never heard of anyone leaving a gap in the weld seams. Your trunnion fitting is a good indicator that you shouldn't. As far as mag well opening size, it's pretty common to have to bend the walls out a little if they caved in from stamping.

    Ive never even seen a PTR flat until I clicked on your link, it's safe to assume the front magwell tabs get cut flush. To me, it sounds like your denial shelf has too wide of an opening. Is it .9" wide outside?

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    Denial shelf is .88 wide and .71 on the inside. here is a pic of it just mocked up.
    I had to lower my resolution to get my pics to go through.


    20180309_170349[1].jpg

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    holescreek's Avatar
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    The long and short of it is that if you leave a gap for the weldment your mag catch pin will be too short to reach the other side. If I remember when I get home from work I can look at my CAD drawings and tell you how wide the weldment inside width should be.

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    I have the inside weldment for the semi paddle mag release, I'll check it for fit in the morning.

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    Daniel,
    I just happen to have one of those shelves and an old ORF flat that was bent but never welded.
    You can see in my photo the receiver is together and this is as far as I can get the shelf to go without forcing it. As it sits, the shelf looks to be spread just a little already.
    I also inserted a magazine to see how the fit would be. The fit was as good with slight friction in and out, not tight, and no wobble.
    Attached Images Attached Images

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    My CAD drawings aren't of that specific area so not much help. Based on a part I used to make the small area the shelf slips over should be around .575~.6" wide. I've never used one of those slip on shelves so none of my Cetmes even has a stub left.

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    holescreek's Avatar
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    I just remembered I have a C308 so I checked the width of the receiver above where they welded the shelf on. .695".

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    Got it welded up today. Welded the two halves snugly together and the narrow piece under the weldment measures .650, a little narrow but everything but the mag fits nicely. Now to work on fitting the mags.

    20180310_214442.jpg
    20180310_214514.jpg

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    Nice welding and clean up work!
    14EH AIT Instructor-PATRIOT Fire Control Enhanced Operator/Maintainer

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