Problem installing PWS FSC91 muzzle device on V51 pistol.
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Thread: Problem installing PWS FSC91 muzzle device on V51 pistol.

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    Default Problem installing PWS FSC91 muzzle device on V51 pistol.

    Hi, all.

    I've run into an odd problem while attempting to install a new PWS FSC91 muzzle device on my Vector Arms V51 pistol. I apologize in advance for all of the photos, but there's a lot to see.

    The day before Thanksgiving, I was able to remove the standard G3 flash hider that came with the V51 without any issues — the retaining spring required the use of a wrench to get it going, but once the spring notch/tab cleared the detents/tines I was able to remove it the rest of the way by hand. The flash hider came off in perfect condition and the barrel threads/tines looked perfectly normal (to me anyhow).







    So far so good.

    I then attempted to install the PWS FSC91 device. It twisted on by hand pretty easily (as expected) and then when the retaining spring notch/tab engaged the tines I needed to use a wrench to get it the rest of the way. It was tight, but was moving along pretty smoothly and easily. And then I noticed the spring appears to have broken — I noticed the end of the retaining spring protruding maybe an 1/8” or so from the device. Looking at the bottom view, you can see where the spring appears to be missing (sheared away) and it even appears like the tines have been peened/smashed in the process. Or it might just be the metal from the spring that got “smeared” (for lack of a better word) across the tines as I was wrenching it on. I stopped there, even though the device was not fully seated, since I wasn’t sure what was going on. This is what I saw when I stopped:









    I wasn't sure if there was any risk in removing the FSC91 (didn't want to cause any more damage to the tines if I could help it), so since I purchased the muzzle device directly from PWS a week or so earlier I opened a trouble ticket with them (warranty issue with the part). They promptly wrote back, asked me to remove the FSC91, and then send them photos of the inside of the device as well as photos of the muzzle. So I did. I was able to remove the FSC91 without any trouble. The tines on the barrel appear to be entirely borked, along with the last one or two turns of the threading itself. I didn't take a photo of the tines before installing the FSC91 (didn't think there would be a problem), but you can clearly see the bright shiny new surface indicating where the retaining spring clearly lathed/milled (whatever you want to call it) the tines and the threading. You can actually see the "machining" marks from where the spring did it's thing. You can also clearly see all the debris in the FSC91 and on the muzzle. In one of the photos, you can clearly see the debris dust on the bench I was using. So, clearly, is seems like something didn't work the way it was supposed to.



















    PWS got back to me this morning (I knew they were out for Thanksgiving, so I didn't expect to hear back from them until today) and their QC manager thinks "something may have been going on with the threads on the rifle. We have sent out a lot of these and have never seen anything like that before. There's a chance the threads on the rifle were just over spec by a little and since the comp you had was made by them it might be set over over sized threads where ours is on the tight side."

    They're sending me a replacement FSC91, so their response is certainly quick... but I'm not sure why another one won't have the same issue. If the PWS device was too tight for these threads, wouldn't the threads be pretty well damaged, too? But it's only the tines that were thrashed. (The rear edge of the muzzle threads seem to be a little beat up now, too, but I'm guessing that happened when I removed the damaged device?)

    I inquired if their QC manager was able to tell from the photos if my barrel's toast. I'm not certain why/how a replacement device would be expected to go on with a different result, but I'm willing to give it another shot. But I would, of course, prefer to avoid trashing my barrel in the process. They wrote back 10 minutes later (I give them absolute props for quick response times, particularly after a long holiday weekend) and stated "some manufactures cut there threads differently. Some stay on the high side of spec, most European type rifles do this. Since HK builds most of there parts for US sales they fall into the same tighter tolerances we use. Most copies are always designed to work with sloppy tolerances so that they will fit on any brand. The new part will ship out today. We would suggest trying to find a thread die that will check your threads and clean up anything that's left over from the prior comp."

    Interestingly, I got a call from Cale at Vector Arms this afternoon regarding an A3 stock set I was purchasing (for my SBR project). His timing was perfect. I told him what happened. Since this particular gun is at least 8-9 years old (I bought it a couple of years ago from a friend who had been using it as a host gun, but I have video of us shooting the gun as an MG back in 2008) he was going back to check S/N records to make sure there wasn't something odd with the barrels back then, but he indicated that all of their V51 builds were done using HK barrels with the standard HK 15x1 threading. (And presumably an HK bird cage FH, too. I think most of their 922 parts were internals.)

    So, PWS is positing that Vector doesn't use high quality/tolerances like HK would use, and instead makes sloppy clones using sloppy barrels and sloppy threading, thus causing the PWS FSC91 muzzle device to have issues. But Vector is saying that, no, they also use HK barrels/threading for their V51 builds, so that PWS device should be a perfect fit.

    So, now I of course have questions...

    First, has anyone ever seen this sort of thing before?

    Second, can anyone tell from the photos if this barrel is salvageable? Can the tines be fixed? Or should it not matter? (I'm not sure how much abuse they can take and still function properly.)

    Third, I don't have a 15x1 threading die. I don't even know if I have another 15x1 threaded device to check for fit... I may have a CETME flash hider in my armorer's kit, but will need to check. Can anyone tell just by looking at the photos if this is in fact not a 15x1 threaded muzzle?

    Finally, what happens if I simply don't use the retaining spring in the FSC91? It looks like I could probably pull it out entirely, but I'm not sure if the threads that are there are tight enough to keep the device from constantly wanting to spin off. I could use an entire bottle of Rocksett, I suppose, if needed. :)

    Thanks in advance for any help you might be able to provide.

    Cheers,

    ~ Greg ~

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    Quote Originally Posted by ptrthgr8 View Post

    ...The day before Thanksgiving, I was able to remove the standard G3 flash hider that came with the V51 without any issues – the retaining spring required the use of a wrench to get it going, but once the spring notch/tab cleared the detents/tines I was able to remove it the rest of the way by hand. The flash hider came off in perfect condition and the barrel threads/tines looked perfectly normal (to me anyhow)....
    The retaining spring is not the reason the flash hider was so hard to get off, it was really wrenched on super tight. The spring is there in case that IF the flash hider were to loosen it won't just spin off easily.

    Quote Originally Posted by ptrthgr8 View Post
    ...I then attempted to install the PWS FSC91 device. It twisted on by hand pretty easily (as expected) and then when the retaining spring notch/tab engaged the tines I needed to use a wrench to get it the rest of the way. It was tight, but was moving along pretty smoothly and easily....
    I resized and overlaid a photo of a G3 barrel onto your pic, best I can tell is that the threads are 15x1 on your barrel because they line up perfectly.
    Notice the red arrow on my barrel, it's pointing to a chamfer. The spring rides up the chamfer and then engages the splines. I'm going to say that forcing the new flash hider on with a wrench is what tore up the front of your splines...the spring appears to have been cutting/wearing in it's own chamfer.

    Problem installing PWS FSC91 muzzle device on V51 pistol.-51-barrel-edit-large-.jpg

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    Quote Originally Posted by 21HK View Post
    The retaining spring is not the reason the flash hider was so hard to get off, it was really wrenched on super tight. The spring is there in case that IF the flash hider were to loosen it won't just spin off easily.
    Perhaps I misspoke when I wrote "wrench." Since there weren't any flats on the bird cage FH that was on there, I stuck a flat handle through the slots and twisted it off. It was the easiest muzzle device removal I've ever encountered. Didn't need to hold the gun between my knees, certainly didn't need to chuck it in a vise or anything like that. I simply wasn't able to twist it off by hand, but once I got it going (2-3 full rotations) with the flat handle, I was able to then remove it by hand. I wish every muzzle device came off as easily. :)

    I resized and overlaid a photo of a G3 barrel onto your pic, best I can tell is that the threads are 15x1 on your barrel because they line up perfectly. Notice the red arrow on my barrel, it's pointing to a chamfer. The spring rides up the chamfer and then engages the splines. I'm going to say that forcing the new flash hider on with a wrench is what tore up the front of your splines...the spring appears to have been cutting/wearing in it's own chamfer.
    Thanks for the photo comparison. The threads do look the same. Are these muzzle devices supposed to be able to be hand tightened? There was no way I was going to get that FSC91 installed by hand. I did use my armorer's wrench to tighten it since it does have the flats machined in the sides. I've never encountered a brake or FH that didn't require some decent amount of torque to get the device properly seated. Are the HK-types completely different? And if so, what would have kept the new FSC91 from going on so easily?

    And I suppose the bigger question is whether or not this barrel is toast. Can the splines be fixed/reshaped? And maybe I'll remove the damaged spring from the FSC91 to see how it screws on without the spring at all.

    Thanks again for you help so far. It's appreciated!

    ~ Greg ~

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    Yes, hand tight for the most part...that's all I've ever done. The HK flash hider design doesn't require it to be timed.
    The barrel profiles are different, as you can see the HK barrel threads don't have a relief cut so the HK flash hider simply bottoms out until snug.

    The relief that's been cut on your barrel behind the threads basically took away material that would/could of been chamfered allowing the spring to ride up before contacting the splines.

    Is it toast? ...I'd say it's buggered up but not completely toast, at least the threads didn't get totally ruined. I know, easy for me to say and I feel your pain.
    Repaired? You'll need to talk to someone that knows more than me about that. Even if it can be repaired, at what cost?

    The FSC flash hider will need to be timed, obviously you don't want the ports just at what ever time they end up when it's tightened. The question is how to time it, there's no material for a crush washer type application to seat against as like on an AR. I don't have any experience with after market flash hiders for HK's.

    I'd go the way your thinking, remove the spring and tighten it down and see where it times....you might luck out!

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    I think your splines could be cleaned up with a dremel and a wheel of appropriate profile, if one exists? Or a small triangle file and some carful hand filing. I would find someone to chase the threads and clean them up. A gunsmith worth his salt ought to have the die.

    There is a flat surface inside the FSC91. You could try a timing washer at the end of the barrel, set down inside the FSC91?? Might have to try several attempts., but filing the washer a little each time until it times out snugly as the thing bottoms out. Like an FAL FH timing washer. I don't think I would add the spring clip in as it appears to be the things that screwed up the tines.

    I would not call that barrel toast because nothing appears to have effected the bore interior. Mostly external cosmetics and once you get something figured, it will all be covered up anyway!

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    Well, it was easy enough to pop that spring out of the FSC91. It threaded right on without any problems, but the timing didn't work out. I wrapped a shop rag around the device and tightened as much as I could by hand and it left the PWS logo on the top of the device at the 7 o'clock position. (If looking at the muzzle head-on.) The instructions indicate the logo should be at the 12 o'clock position. I took an armorer's tool wrench to it and could muscle it to the 11 o'clock position. Other than aesthetics, I'm not sure if there's really a difference between having the PWS logo at the 12 o'clock position vs. the 6 o'clock position. But I would have to loosen it a tad to get it back to the 6 o'clock spot, which would then make me worry about the thing coming loose while firing. And I don't really want to use a ton of Rocksett to keep in in place.

    I'm not sure I could use a washer/spacer to get the timing right. The older models of the FSC91 used a crush washer inside the device and an Allen screw through the bottom of the device to engage the tines in the correct position. The new model, like the one I have, use only the retaining spring. There's no significant flat spot on the inside of this FSC91 and the washer/spacer would end up being sandwiched between the muzzle crown and the "cone" (for lack of a better word) on the inside of the device. I'd be concerned that even if I could get it lined up correctly during the installation that it might still work itself loose enough to cause a bullet strike of some sort.

    Installing the FSC91 sans retaining spring sorta smoothed out some of the damaged tines, but still not enough that I was able to get the original bird cage FH back on using hand power. (I didn't try using a tool of any sort because I didn't want to risk damaging the spring on the FH.)

    At this point I think my next step is to try to gently reshape the tines. I have a Dremel tool with all sorts of bits and also have a set of jewelers files, so I'll see what I can do with those. If I can get the original G3 flash hider back on and secured, I'm just going to give up on the FSC91. It looks cool at all get out, but it's been the biggest pain in the rear I've ever experienced. Well, with muzzle devices anyhow. :)

    Thanks again for your help, all. I'll report back in once I've had a chance to work on those tines a bit.

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    Quick update.

    I wanted to see if perhaps the FSC91 was a little narrower than the G3 flash hider that was originally on the V51. I.e maybe it was too tight, which maybe contributed to the problem I encountered. Using a digital caliper (cheap Frankford Arsenal one, but pretty decent) I measured the outside diameter of the tines at 16.00 mm. I measured the insider diameter of the G3 flash hider (the wall before hitting the threads) to be 16.08 mm. I measured the inside diameter of the FSC91 (same area) and got 17.90 mm. So, the FSC91 has an inside diameter that's ~1.84 mm larger than the G3 bird cage... so if the G3 FH fits, I would think the FSC91 ought to easily. Interesting.

    I was able to get the original G3 bird cage back on with hardly any effort - didn't need to grind or file the damaged tines at all. Just had to give it a little extra oomph to get the spring over the tines initially, but otherwise it was super easy to hand tighten back into the secured position. If you look at the photos I posted earlier, the spring on the FSC91 appears to have basically beveled the forward edge of the tines. When the new FSC91 shows up, I'll see how far out that spring/notch sticks and maybe it's just a matter of pushing the spring out a bit before actually installing it. It's possible that newly beveled edge will help push the retainer spring up and over the tines this time, rather than through them like it did last time. And this time I know what to look for.

    But at the very least, since I was able to easily get the G3 FH back on, I would say the only casualty here is the FSC91 retaining spring. If that's the worst of it, I can live with that outcome. :)

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    Glad it's working out for you.
    I did some more playing around last night after looking at the serrations on the G3 barrel. Besides the chamfer that allows the spring to ride up before contacting the serrated teeth during installation, this section of the barrel is also tapered.


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    Quote Originally Posted by 21HK View Post
    Glad it's working out for you.
    I did some more playing around last night after looking at the serrations on the G3 barrel. Besides the chamfer that allows the spring to ride up before contacting the serrated teeth during installation, this section of the barrel is also tapered.
    That's a great visual. Thanks for sharing. It would seem that the FSC91 spring lathed off a good portion of the tapered end of that section. So, it will be interesting to see how well the spring now keeps it in place.

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    I installed the same primary weapons brake on my 10 to 12 year old vector 51that has always run flawless.
    But I have to say a little tough on recoil until I installed the brake and a bill Springfield enhanced buffer in the A2 stock.
    When installing the brake I found I had to remove the internal crush sleave for the break to install all the way up on barrel
    Properly.I was able to install completely by hand and spring clip keeps break in proper clocked position.
    Between both upgrades they completely tamed the 51 in to a fun (in full auto) and pleasure to shoot toy.The best part of the brake is
    After a few rounds down range you don't have to worry about feeling crowded on either side of you at the range any longer.
    If you have any question or need additional pictures PM me and I can provide you my phone number so you can call me and I can text you some close up pictures of the break installed and barrel threads.
    Attached Thumbnails Attached Thumbnails Problem installing PWS FSC91 muzzle device on V51 pistol.-20170912_211031.jpg   Problem installing PWS FSC91 muzzle device on V51 pistol.-20170912_211417.jpg   Problem installing PWS FSC91 muzzle device on V51 pistol.-20170912_212731.jpg  

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