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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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

 

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.

 

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.

 

I HAD THE SAME PROBLEM!


Had my Trident approved last summer and got a 3 lug mount a couple months ago. Got home and tried to put the 3 lug on and it only went .5 inches on, I was bummed! I thought no way I sbred my CA89 and my 3 lug is out of spec. I didn't give up and sprayed remoil over everything. I kept taking it on and off and after one firm push the mount went down enough to rotate over the lugs. Now the can slides on perfect with no wobble. Just took a little breaking in. At first I thought no way my barrel was in spec, the mount wouldn't move at all but I just kept taking it on and off.

 

The correct dimension for the nose of the barrel is 15mm or about .5906. I turn that dimension to .590+-.0004 on the adapters and barrels I make and I make a lot of them. The barrel sounds like it's oversize and if so that's the part you want to fix. You don't say how you measured the SWR mount ID at .597 but you CANNOT measure that with calipers with a sufficent degree of accuracy so that part may well be inspec. Does it fit on your dealers MP5?

 

This is a common problem. I have seen it with a SW5 an V89 I owned.

In the SW5, the problem was too much finish. a few minutes of sandpaper took off enough finish to solve the problem.

In the V89, the lugs were the problem. 30 seconds of dremel removed the bumpy edges of the lugs and solved the problem.

 

I seem to recall reading that approach on one of the threads too. It took some sandpapering to the lugs to make it fit. Try that approach first and maybe some remoil and see what happens.

 

This shows the sandpaper and slight dremel work needed to get a 3-lug device to fit a SW5-FS. The hole in the bottom of the lug is because it originally had pinned faker silencer before I SBR'ed it:

 

You don't say how you measured the SWR mount ID at .597 but you CANNOT measure that with calipers with a sufficent degree of accuracy so that part may well be inspec. Does it fit on your dealers MP5?

I measured the the mount about 50 times and got an average, of what Id I got the most. I would say it is pretty good. It was very tight on the Dealer MP5 and that was a used gun with wear.

 

the concern i have in reading the fixes is that 1) done by hand improperly, it is likely to result in an unbalanced lock up, 2) the breaking in method mentioned (lube and repeated on/off fitting) may still not do the trick in the long run. just be aware that with extended firing, the barrel will heat up and again, minimize the clearance between mating surfaces. occasionally, you hear of tri-lock lock up, resulting in failure to release the can when you're done shooting. heat and grit contributes to this. you also need to be clear whether it's a lug clearance issue, or a barrel nose/thread protector issue. always be very careful in what you sand/file down. use the same care you would if you were tuning a trigger. the tolerances and dangers are similar with both proper barrel/can alignment as well as trigger sears.

 

Well, this is what happens when you buy a clone, and why they cost $hundreds less. If you want hassle free, install a real MP5 3-Lug BBL.


ETA:

Didn't mean it that snappy. Meant to point out clones have some extra work to make them go 100%.

 

My experience on a brand new PTR 9 KT was similar to what others have posted here as it relates to the tri lug fit issues. This isn't my 1st rodeo with tri lugs and cans so i knew there could be some compatibility issues.
I tried with the thread protector, without the thread protector, with and without the O ring and then kind of gave up thinking I'll need to take this to a real gunsmith to get resolved if I want the tri lug convenience. Then I decided to really get down to where the issue was and for my gun, everything was in spec (based on careful micrometer measurement comparison to two other tri lug set ups) except the area between the lugs and where the threads are cut. The difference was about 4 / 1000ths which seems like nothing but it was everything. Anyone that reloads precision ammo understands. I polished the area with a felt Dremel tip at medium speed then high speed with Flitz. Then i did the same to the inside spacer (not the tri lug adapter) on my Octaine can and BAM, MERICA LIFE IS GOOD it worked!

I added just a trace of synthetic G96 to the contact surfaces where I polished the area forward of the lugs on the barrel and the can spacer inside, and it works perfectly. I sure hope this saves someone else some trouble.

 

Modify the barrel. I have a C89 and the can did not fit. No way it was going to fit. However, it did fit another Todd gun that was put together by DJ Getz. Fit with NO slop. SO rather mod the can, make the barrel it the can.There will be other guns you will try use the can with. Don't frak with the can.