Vulcan moderator problem... help?

I know the problem, I'm hoping someone out there has a good solution for me!

I have a problem with my mint condition Vulcan .25 (not Vulcan 2), it is really an odd problem.  The gun used to shoot great & accurate, then one day it was shooting all over the place, I finally figured out that the pellets were slightly rubbing the moderator (DonnyFL) exit hole.  I tried it with 2 other moderators and it was the same problem.  When I shoot it without any external moderator it shoots nice & accurate as before.  At first I thought the shroud/moderator adapter part  was warped or damaged, but it seemed centered as far as I could determine.

In USA, almost all moderators have a 1/2"x20tpi thread, right?  But the Vulcans have a M14x1.25mm external thread.  This is size is very close, and "seems" to be the same, BUT IT IS NOT THE SAME!  It is just lose enough that the moderator can cant (sit slightly eccentric) on the shroud (as mine did).  With the eye, it looks OK, but in reality, it is not center or concentric, so the pellets can brush against the exit hole of the moderator. My .25 moderators have an exit hole of .312", I can drill the exit hole on my moderator .400" or more, and I think this defeats the function of the moderator.

So now I know what the problem is, but I am not sure how to correct the problem.  I tried to use teflon tape on the threads, it tightened up the threads, but did not force it to sit perfectly center.  I also tried to add an o-ring between the moderator and the shroud to compress as it tightens, but again... it tightens it up good, but does nothing to center the shroud on the very loose undersized threads.

Does anyone have any INTELLIGENT ideas or suggestions?

You'll never get the two threads to match properly. The only solution is a properly threaded adapter.

Call/text/email Donny.

Clean up any damage on your factory shroud and get the correct Moderator:

https://donnyfl.com/collections/ldc/products/1-5-x-6-5-inch-sumo?variant=13285825216555

The problem might be barrel harmonics especially so if the barrel is free floating, adding a mod changes the harmonics and the POI. 

Jeez...this isn't brain surgery!  Toss the OEM adapter, get the 1.2 X 20 air gun adapter from DonnyFL and your problems will resolve.

Hoot

Hepotter, I did say "Does anyone have any INTELLIGENT ideas or suggestions" but I guess you missed that part?  You obviously don't have any idea what part I'm referring to or you would not have make your dumb & insulting comment.

Just FYI for other readers, those who may have Vulcans.  If you have to butt your mod down firmly to get your mod not to wobble, you do NOT have correct thread mating, and your mod may be eccentric, or it can get bumped eccentric at any time.   DonnyFL now sells mods with the M14-1.25mm thread, BUT it does not fit the Vulcan M14 threads properly (fits just as loose as the 1/2-20 mod).  DonnyFL is such a great guy, he is working with me so he can provide a snug & proper fitting mod for the Vulcan.  I will update this thread when resolved.

@tjscustom Hi, I know it has been some time since you posted this thread but I am experiencing a similar issue on my Vulcan 2 when using a Eagle Vision 1/2" UNF to 14mm converter. The rifle shoots very accurate without a Moderator on but like a shotgun with one. I have noticed that pellets are actually clipping the adaptor which surprised me as it is only sticks out about 1/2" past the muzzle of the shroud (photo attached).

I am thinking shroud alignment but thought I would reach out to you and see if you found out what was happening on yours.

Any help would be appreciated.

I'm not sure what you already know or what I already posted. The short version is the Vuncan male threads are at the MINIMUM tolerance of M14, and the DonyFL female threads are at the MAXIMUM tolerance, which makes a horrible wobble. IF I remember right, I think I gave up and wrapped teflon tape layered with blue locktite making the fit very tight, and then just hand&eye tighten it very strong to what appears center. On another gun I had the same trouble and just made a moderator myself and barely threaded the female so it was undersized and that worked well. I also had a Vixen with a different problem, the OEM moderator was completely useless, so I fabricated an oversize shroud-moderator. Sorry I am not giving you any magic answers here. Best of luck.

Thanks for your reply, my metric to 1/2" UNF mod adapter fits the thread on the shroud very well and tight so I am thinking that the chap I bought the Vulcan 2 from had banged the shroud and put it into misalignment. I am going to check out the shroud alignment today to see if the softer aluminium inner thread has been bent in relation to the steel barrel thread. The shroud looks ok to the eye but may not when I put a steel ruler along it and the breech block.

It is clipping so close to the muzzle I cannot believe it can be anything else. Aside from that it shoots extremely well with super tight groups.

Thanks again for coming back to me, I'll post the results of my investigation when I hopefully find out what is happening 👍