So, I purchased a Palmetto State Armory .300 blackout complete upper I intend to use with my SilencerCo 7.62 SAKER and SiCo Trifecta Flash Hider.

This is the barrel on my upper; (pic from PSA website) ETA- Upon further comparison, mine is a slightly different profile with the last step being closer to the muzzle but still very similar.


Notice that there is very little shoulder behind the threaded muzzle. What little there is, has more of a radius than squared.

So, I installed my Trifecta Flash Hider and torqued it down to between 20 to 30 ft.lbs as recommended by SiCo (I set my wrench to 25 ft.lbs. compensated for +1" addition of the crows foot open box socket)

When I mounted my SAKER and ran an alignment rod through, this is what I found;


Obviously not good. I have used these Geissele rods to verify alignment  on every can/barrel combination I have used and never discovered a problem before. I was beginning to think they were a waste of money! However, I was glad I discovered this before sending a bullet through this set-up.

I removed the Trifecta Flash Hider and installed it again two more times at lower and higher torque settings within the recommended range. The alignment rod test results were about the same each time just orientated in a different way, off-center. Also, while 20 - 30 ft.lbs is not very much torque, the flash hider came off with almost no effort each time I removed it. I just don't think it had anything square and substantial to bear against.

So, where do I go from here? I truly believe the problem is the lack of a square and substantial shoulder behind the muzzle threads. I need to use a SiCo MAAD module compatible muzzle device as that is the only .30 cal can I have and I like the set-up. It was suggested in another arfcom thread HERE to consider an adapter like that made for the SCAR17 barrel (which also lacks a proper shoulder for suppressor use) but I have not found anything regarding it's use on other barrels. I don't even know if the barrel diameter is the same as the SCAR17.

So, is this something correctable or should I just find a new barrel? I really have no interest in .300 Blackout without suppressor capability.

Thank you all for any input and advice.

One fix is to chuck it up in a lathe & make an undercut/thread relief IF there is enough minimum diameter to do so. Second, and this could be done either way, is to make a barrel collar that threads on first, then run the muzzle device down & use the collar to both time the device & provide a shoulder. The collar has to be precise in fit & the shoulder has to be perfect, and I mean damn near .0001 perfect otherwise you risk stacking tolerances.

Baffle strikes are expensive.

Thanks for the response.

Neither of those options are within my humble abilities. Any suggestion for someone I could send my upper and flash hider to who could do those things?

Also, could someone (again, not me, someone competent) properly align the flash hider and the barrel and then weld/solder/pin the muzzle device permanently installed (and aligned)?

Have you considered a direct thread mount for the suppressor?

I'd have to change the MAAD mount to a direct thread and I'd loose the simplicity of being able to use it on multiple rifles at will.

Also, since the barrel seems to be lacking a proper shoulder, wouldn't I still have the same problem with a direct thread??? (I don't know)

You will still have the same problem. Direct thread mounts still need a shoulder to react against (provide alignment and torque to stay put). You might look at some of the SCAR solutions or some muzzle brakes can index off of the muzzle but I'm not sure if SilencerCo's are designed with that in mind. Maybe give customer service a call, it's free!

What is the diameter of the barrel directly behind the threads?  .725" is the minimum usually recommended for 5/8-24.
The correct and best solutions listed above all say the same thing: get the shoulder squared away.  The direct thread mount won't work any better if the shoulder is not fixed first.
Squaring the shoulder is very simple, and should take the slowest machinist all of 20 minutes, making sure he indexes off the bore, not the outside of the barrel.
The threaded collar suggestion is another positive way to fix it, and the only way, if your barrel diameter as mentioned above is too small. But, this could cost more than you'd like.
PSA builds and sells a lot of ARs and uppers. I don't know if they can fix this for you, but it can't hurt to ask them.  Welding should be your absolute last (or never) solution.

I posted a while back about a friends nearly identical shoulder problem from another manufacturer.  
It caused the peel washer to deform around the radius, resulting in a very slight (paint only) strike on a TBAC can.  Corrected the shoulder, and it's now perfectly centered.

Why would contacting PA and sending it back not be an option? All the other suggestions seem like a bandaid and not a solution. I wouldn't even think about shooting that barrel with a suppressor on it. I'd send it back, demand a full refund, and buy a better brand barrel.

Does the Trifecta flash hider have the ability to register on the perpendicular muzzle face, rather than a shoulder located in the more common location behind the threads? Many manufacturers design their flash hiders so that they can index both at the conventional location against a perpendicular shoulder behind the barrel, or against a perpendicular muzzle face, as is the case with the SCAR-17 barrel. This is most easily accomplished with a flash hider that does not have to be rotationally indexed with shims. I'm not very familiar with the Trifecta Flash Hiders, so please excuse my ignorance.

Most 5/8-24 threaded barrels (most, not all) have a right at .600-.620 length of threads before the shoulder. Given that the barrel diameter at the conventional shoulder location is inadequate for a proper interface between the rear face of the flash hider and the barrel, you could get the thread relief behind the threads on the barrel lengthened enough so that the Trifecta flash hider does not hit the vestigial shoulder and bottoms out against the muzzle face. This would work if the Trifecta flash hider has a perpendicular front indexing surface and does not need to be shimmed.

If the above-described method would work, it would be far preferable (IMO) to adding any kind of adapter between the barrel and the Trifecta flash hider.

Mike Smith/AAC
SilentMike

Mine measures .695 in diameter uniformly around the barrel. The threaded area measures .620 major diameter.

(measured with my zeroed Lyman 6" Dial Caliper)


Thank you for the response and input. This is all good stuff to consider.

I do not know if the Trifecta was designed to be indexed off the muzzle face. I e-mailed Silencerco asking for some technical input. However, there is a LOT of room between the muzzle face and where it would contact the Trifecta mount. It is not even close to making contact. The existing shoulder would have to be relieved back 1/8" or more (just a guesstimate)

I do not need to time the Trifecta so IF I can get it squared against the muzzle face that would work for my application.

I will have to measure the length of the threaded area. ETA- Hard to measure since the shoulder is not well defined but I am measuring .560"+/-
.620" including the relief area behind the threads.


Thank you for your insight and input. Very helpful.

Thanks for the response.

I sent an e-mail to both PSA and Silencerco asking for some technical guidance.

Well, from the shop drawings posted on Silencerco's website it looks like the "minimum" barrel diameter at the shoulder they require is .720". At .695", my PSA barrel is no where near that

So, short of figuring out a way to index off the muzzle face, this barrel is not going to work for me

Also, I suspect any machine work required to "make" this barrel work would cost more than just buying a new barrel with the required dimensions to properly mount my suppressor.

Right. Send it back.  PSA should have known better or checked their product specs better before pushing it out the door.