Can to 3-Lug Problem
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Thread: Can to 3-Lug Problem

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    Default Can to 3-Lug Problem

    I have decided to take my CA-89 to a SBR and put a SWR Trident-9 on it. I am going with a 3lug mount. I have all the paperwork in, the can is at my class III and everything is good, until I tried to fit it to the gun. The 3lug adapter will not fit over the 3lug. My class III dealer fit it to a real MP5, and a new ca89k snug. I checked the dimensions of the 3lug and came up with about 0.592 to 0.594, which seems a little bigger than what it should be (0.591?). But when I measured the SWR 3lug mount it measured about 0.587. So part needs to be fixed, or is easier to fix? Thanks for help.
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    Quote Originally Posted by c-venn View Post
    I have decided to take my CA-89 to a SBR and put a SWR Trident-9 on it. I am going with a 3lug mount. I have all the paperwork in, the can is at my class III and everything is good, until I tried to fit it to the gun. The 3lug adapter will not fit over the 3lug. My class III dealer fit it to a real MP5, and a new ca89k snug. I checked the dimensions of the 3lug and came up with about 0.592 to 0.594, which seems a little bigger than what it should be (0.591?). But when I measured the SWR 3lug mount it measured about 0.587. So part needs to be fixed, or is easier to fix? Thanks for help.
    If your 3 lug is threaded and has a knurled thread protector, the knurls may not be allowing the 3 lug to enter the piston...happened to me. I ran mine without the thread protector until I could find a protector without knurls.

    Whether the 3 lug is threaded or not, see below....

    The piston inner diameter may be out of spec from SWR...happened to me also. Had to send my piston in and get a new one that was in spec. Contact Henry from SWR and he will talk you through it.

    Good luck.
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    CA-89 seem to be notorious for having out-of-spec noses on
    the tri-lug. hope (as rollin stated) you have a thread protector
    instead of a simple, unthreaded tri-lug.

    it would be much easier to get a proper TP with the proper
    critical specs, otherwise you may need to turn it......or, to
    have the can's adaptor/mount tweaked by the manuf.

    don't try to do this yourself, as you may unintentially end up
    with an alignment which is not concentric to bore, spoiling point
    of aim, or worse, baffle strikes.
    Last edited by raymond-; 07-18-2009 at 04:52 AM.
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    There is no threads on the BBL, so I need to either tweek the BBL or the can mount. The funny thing is the BBL seems to be more in spec the SWR part.

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    I just measured my gen-you-wine HK MP5-N barrel. The thread protector is the one with the fine knurls. Both the thread protector and the bit of smooth barrel diameter just before the lugs are exactly .590000". So if the ID of your 3 lug adapter is only .587, it's not going to fit. I don't see how it could have fit on your dealer's MP5.

    And also, just a thread protector won't fix the problem. There is a ring of smooth barrel between where the thread protector stops, and the lugs begin. That would have to be turned down as well.

    It sounds like your adapter is undersized. The best advice is probably to get an accurate measurement of your thread protector, and that sliver of barrel before the lugs, and the lug widths as well, and give that info to SWR.

    Edit: never mind about the thread protector, since you have a normal MP5 type barrel. And it sounds like it's not oversized, your problem looks to be with the SWR adapter.
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    Yes I am thinking both are out of spec, and that is why they are not fitting. But it seems the SWR part is more out of spec. I think I will contact them tomorrow and see what they say.

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    Quote Originally Posted by c-venn View Post
    Yes I am thinking both are out of spec, and that is why they are not fitting. But it seems the SWR part is more out of spec. I think I will contact them tomorrow and see what they say.
    They could be. My guess is that the barrel diameter is specified at 15.0 mm, which is .590551". Tight tolerances for metric drawings are usually +/- .01mm, which would allow for barrel diameters of .5901 and .5909.

    Production tolerances are usually .1mm, but that seems like it would be too much for suppressor use.

    So yeah, you proably have both out of spec. You may actually be lucky that they both are, as if your suppressor adapter was correct but your barrel was the only part that's oversized, SWR may have a problem with fixing the adapter for free when it's your barrel that is out of spec. Then again, maybe they wouldn't care, their customer service is supposed to be pretty good.

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    Phil Dater is very aware of this critical specification. He sent me a TP, gratus, as he felt that the one which came with my S&H rebarrel was not up to snuff, ie, a little on the small side. The one Phil gave me is mic-ed at .591 just now. It hasn't had much use so on the surface, it would appear that the mount on the can may be off. find out what the manuf says though

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    Default Piston

    I forget the measurement of my old piston now, but when I talked to Henry about it awhile back, he encouraged me to send it in because he was just as courious about the i.d. being out of spec as I was.

    He never explained how or why it happened, but did send me another piston before I even shipped the old one to him. Henry is not the most exciting guy to talk to but he has very good customer support from my experience.
    Last edited by rollin_hot; 07-17-2009 at 05:44 AM.

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    I would tend to side with Raymond on this one. It wouldn't suprise me if your CA89 3 lug is out of spec. The 3 lug on my CA89 was out of spec and wouldn't accept a factory HK flash hider. I've since sold it for that and other reasons. He who must not be named's forum has several threads about it if I recall as well and some workarounds/solution. Some involved modifying the 3 lug itself I think. Check there.

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