Pressing barrel into trunion - installation jig
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    Default Pressing barrel into trunion - installation jig

    I’m looking to make a barrel press jig that includes a ram with a shoulder that limits the pressing depth by contacting the back of the trunion. I plan on making several of these in .001 increments so I can easily set the perfect bolt gap without having to deal with the barrel “jumping” too far.

    Can someone who has taken the time to measure the distance from the back of the MP5 trunion to the back of the barrel please post that measurement? Thanks in advance.

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    that's a really good idea, I may have to steal it! that or ill just keep wacking on my shop press with a mallet to try and get the barrels to move a tiny bit lol!

    I do think the depth would vary from gun to gun a bit though, some of my barrels seem more flush with the trunnion than others

    ill get you a rough measurement later

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    I think the issue may be that when you’re trying to press .001”, it sticks and doesn’t move. So, you go to the next one and it sticks, and so on, until it finally slips and you’re too far. The slipping and sticking is caused by the flexing of the press and preventing it requires a more rigid press. That said, I hope I’m wrong and I wish you success.
    Ferdfarming likes this.

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    Quote Originally Posted by Ferdfarming View Post
    that's a really good idea, I may have to steal it! that or ill just keep wacking on my shop press with a mallet to try and get the barrels to move a tiny bit lol!

    I do think the depth would vary from gun to gun a bit though, some of my barrels seem more flush with the trunnion than others

    ill get you a rough measurement later
    I have no doubt that the measurement will vary slightly from gun to gun due to manufacturing tolerances - just looking for a starting point. Any help is appreciated!

    The more I think about it, the more I realize that a two piece ram would be best. The upper piece with a diameter that rests on the back of the trunion and a lower piece that consists of a series of graduated length cylinders with a diameter that just fits inside the trunion body.

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    Quote Originally Posted by tlrgsxr View Post
    I think the issue may be that when you’re trying to press .001”, it sticks and doesn’t move. So, you go to the next one and it sticks, and so on, until it finally slips and you’re too far. The slipping and sticking is caused by the flexing of the press and preventing it requires a more rigid press. That said, I hope I’m wrong and I wish you success.
    I don’t claim to be a mechanical engineer but here are my thoughts:

    I have no doubt that a smaller, less rigid press will increase the slipping issue due to flexing. I read somewhere where it generally takes 3-4 tons of pressure to move the barrel (I have a 20 ton press). Taking into account that the force required to overcome the friction between the barrel and trunnion and to start the barrel moving will always be greater that the amount of force required to keep it moving, it is impossible to completely eliminate all jumping. Because of this fact, if you limit the movement of the ram to an increasingly smaller amount - you will eventually get to a point that the limited movement will be less that the amount of barrel jump. I think that in the real world and when using a sufficiently rigid press, this does not significantly affect the ability move the barrel in .001” increments. There is only one way to know for sure and some control over the barrel’s movement is better than no control.

    You can’t tell me that HK and the various clone manufacturers don’t use a similar setup to press their barrels. Pressing a barrel without some method of measuring/controlling ram movement is like chambering a barrel without using the tailstock to measure/control the movement of the reamer. It can be done and if you attempt it enough times, you will eventually get lucky and achieve an acceptable result. There are better way of performing this task that will greatly increase your chances of doing it right the first time. Just trying to find one of those ways…
    Last edited by Max.Elorza; 02-03-2019 at 05:18 PM. Reason: Spelling

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    i suspect those manufacturers & gunsmiths simply have a more rigid press (and some measuring tools like you mentioned).

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    Quote Originally Posted by Max.Elorza View Post
    I have no doubt that the measurement will vary slightly from gun to gun due to manufacturing tolerances - just looking for a starting point. Any help is appreciated!

    The more I think about it, the more I realize that a two piece ram would be best. The upper piece with a diameter that rests on the back of the trunion and a lower piece that consists of a series of graduated length cylinders with a diameter that just fits inside the trunion body.
    I am measuring around 1 1/8"-1 1/4" from the barrel to the end of the trunnion where it meets receiver rails on two guns I measured.

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    Quote Originally Posted by Max.Elorza View Post
    I don’t claim to be a mechanical engineer but here are my thoughts:

    I have no doubt that a smaller, less rigid press will increase the slipping issue due to flexing. I read somewhere where it generally takes 3-4 tons of pressure to move the barrel (I have a 20 ton press). Taking into account that the force required to overcome the friction between the barrel and trunnion and to start the barrel moving will always be greater that the amount of force required to keep it moving, it is impossible to completely eliminate all jumping. Because of this fact, if you limit the movement of the ram to an increasingly smaller amount - you will eventually get to a point that the limited movement will be less that the amount of barrel jump. I think that in the real world and when using a sufficiently rigid press, this does not significantly affect the ability move the barrel in .001” increments. There is only one way to know for sure and some control over the barrel’s movement is better than no control.

    You can’t tell me that HK and the various clone manufacturers don’t use a similar setup to press their barrels. Pressing a barrel without some method of measuring/controlling ram movement is like chambering a barrel without using the tailstock to measure/control the movement of the reamer. It can be done and if you attempt it enough times, you will eventually get lucky and achieve an acceptable result. There are better way of performing this task that will greatly increase your chances of doing it right the first time. Just trying to find one of those ways…
    I have a measly 12 ton press and I have managed to get good bolt gap on 7 different hk clone builds so far. there is a method to my madness; I get it close and then I start gradually increasing the force in the press while taking pauses to wack the top of the press with a 5lb mallet and the force of the mallet will cause the barrel to move in small increments rather than large. it actually works pretty good but sometimes I have to press barrel through and try again. I tend to just "play the barrel lottery" and keep pressing till I land on the right depth. I really regret not spending the extra money for 20 ton press but I make due. even with 12 ton press it can be done no reason to over think it but I do really like your idea..


    anyways I hope it works out and my measurement provides good starting point for you. Cheers!!
    Last edited by Ferdfarming; 02-04-2019 at 03:02 AM.

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