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Thread: build question on barrel pressing about bolt gap

  1. #1
    Veteran thedave8's Avatar
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    build question on barrel pressing about bolt gap

    If i wanted to press barrel in trunnion while trunnion is out of reciever and get the right bolt gap, how does one go about it.....scince in the reciever you would want pressure against closed bolt(hammer down).....just insert and lock bolt assembly and maybe just push firmly against it to simulate "hammer down" and then measure? or is this not the advised way to go?

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    Otis61's Avatar
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    Seems like I heard the answer to this, but can't remember. I have two more to press myself. My first CETME was also my first build ever, and I was all excited, and didn't take too much time to read and learn all the little tricks to this build. I also didn't have access to a press. So I took an old FH and pounded the barrel on with a BFH. I also used the existing notch for the barrel pin, resulting in a .004 bolt gap on the completed rifle. I wouldn't recommend what I did to anyone. Although now, after a new bolt head, locking peace, and +4 rollers, I do have a well shooting rifle with .020 bolt gap. The down side is if I ever shoot this enough that the bolt gap go's down below .004 again I'll have to repress the barrel. Which will be a PITA

  3. #3
    Senior Veteran cfish's Avatar
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    Could you not just replace the rollers again as the bolt gap closes?


    COG#1963

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    Veteran thedave8's Avatar
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    Quote Originally Posted by Otis61 View Post
    Seems like I heard the answer to this, but can't remember. I have two more to press myself. My first CETME was also my first build ever, and I was all excited, and didn't take too much time to read and learn all the little tricks to this build. I also didn't have access to a press. So I took an old FH and pounded the barrel on with a BFH. I also used the existing notch for the barrel pin, resulting in a .004 bolt gap on the completed rifle. I wouldn't recommend what I did to anyone. Although now, after a new bolt head, locking peace, and +4 rollers, I do have a well shooting rifle with .020 bolt gap. The down side is if I ever shoot this enough that the bolt gap go's down below .004 again I'll have to repress the barrel. Which will be a PITA
    Otis, I shoulda picked your brain some more ,thanks for the info.... anyone else have their experiences?.....

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    Militant Asshole Big Steve's Avatar
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    You can do it. But you should slide it into the receiver to hold the bolt and carrier nice and straight when you check your gap. Make sure you chamfer the sharp edges your trunnion before you press it, or it may peel metal off your barrel. Use never seize also.
    Steve

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    Veteran thedave8's Avatar
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    Quote Originally Posted by Big Steve View Post
    You can do it. But you should slide it into the receiver to hold the bolt and carrier nice and straight when you check your gap. Make sure you chamfer the sharp edges your trunnion before you press it, or it may peel metal off your barrel. Use never seize also.
    Steve
    good idea......chamfer.........dont have reciever bent..waiting for the jig, but wanted to press barrel ahead o time.........

  7. #7
    Veteran Daffy's Avatar
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    CFish, replacing just the rollers is a "quick fix". The parts that are wearing down also need replacing for a proper fix. Actually, I've measured a handfull of rollers on worn out kits (with bad gap), the rollers showed vertually no wear, excetp one (one roller, not the pair) . The majority of wear is on the bolt head and locking piece. You can clearly see it with the naked eye in good lighting. I can't get a good enough look to see how the wear was on trunnions nor chamber without removing barrels from trunnion.
    Actully, if you look at the wear spots on the locking piece and bolt head, you will see that the rollers have worn a nice little pocket for themselves. These pockets make it much harder for the rollers to move off that spot as they are now seated in that wear groove. So the rollers actually trying to push the head forward to get out of that groove, as the head is trying to push back on the rollers which increases wear even faster, instead of freelying sliding off the the side like they should be doing. Same as on the locking piece.
    So best thing to do is replace the locking piece, bolt head and rollers.
    Its like working on a gear box, you don't just change one gear, you change them as a set. If you replace these 3 parts, you may not even need over sized rollers.
    I've got a used trunnion on the way that I plan to cut in half. I can then see if the trunnion is also getting this pocket worn into it. I hope not as its not so ease to replace. It may be harder metal to prevent this. Problem is I don't know how much use this one trunnion had durring its life.

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    Veteran thedave8's Avatar
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    all good info, anyone else had experience with question at hand?

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