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Recommendations for SCAR 17S barrel work…..

9K views 37 replies 11 participants last post by  themao 
#1 ·
Who would any of you recommend to repair threads on a SCAR 17s barrel? I am actually thinking of just having it cut down to 14.5-15” and pin/weld the FH on as well.

To make a long story short, I use a Surefire FH and SOCOM 762 can. I had a very prominent smith install it. It is no longer concentric. I believe the threads are not concentric, as I removed the FH and checked it without the installed shoulder ring and Surefire shims.

I really wish FN made these barrels with a larger shoulder. I’m seriously thinking about just buying a Deadshot barrel.
 
#5 ·
If you're only concerned with chasing the threads a proper size and pitch die will do that. If the factory threads are not concentric with the bore which is difficult to fathom the only solution would be to chop the threads off and start over.

The bigger question is, how did you determine the barrel's threads are causing concentricity problems?

As others have said Jarod at PMM is well known for quality work...
 
#6 ·
I removed the flash hider, shoulder ring and shims. I screwed back on the FH and mounted the Surefire SOCOM 762. I then inserted a Geissele alignment rod. It is still off but not nearly as bad as it was mounted.

When I mount the Surefire SOCOM 762 on my 5.56 ARs I run suppressed, it’s concentric. I checked it again with a 5.56 Geissele alignment rod. When I mount my Surefire Genesis can on my Tikka, it’s concentric with the 762 Geissele alignment rod.

When I install the original washer that came with the PWS muzzle brake on my rifle (way back from 2012), add the Surefire FH and SOCOM can, it’s still slightly off when measured with the Geissele rod.

Not sure what else it would be. Geissele makes good alignment rods along with all of their parts. My other 5.56 Surefire equipped ARs are all concentric (Daniel Defense, Geissele uppers with surefire FHs). My Galil ACE 7.62x39 SBR is concentric as well when using the same SOCOM 7.62 can and Geissele rod.

You are correct, I was thinking chop barrel to 14.5-15” and pin/weld on Surefire FH. I’d like to get 10k rounds out of the FN barrel if I can, as I shoot mostly M80 ball out of my SCAR. My Tikka eats the match ammo (it’s a CTR that sits in a KRG Whiskey chassis).

Again, I don’t understand why FN doesn’t put a decent shoulder on these barrels.
 
#7 ·
As bizarre as it would be for a company that's been making barrels for as long and as well as Herstal has it sounds to me like your bore isn't straight. If my suspicion is correct no amount of chopping and threading will work. You can check this yourself with a micrometer by measuring the thickness from bore I.D. to barrel O.D. at the muzzle if it's off at all the barrel is the culprit. A barrel is threaded in a production capacity with an annular cutter followed by a die not a lathe and a die is self-centering therefore it's nearly impossible for the threads to be anything other than concentric with the barrels center. However, a barrel can be bored out of longitudinal alignment with it's true center axis. A micrometer will definitely confirm this.

Another potential issue could be the miniscule shoulder the SCAR's pencil barrel has. If the shoulder isn't completely square with the bore's center any muzzle device will skew under tension. For this you could check by simply screwing on the FH without contacting the shoulder then check with the rod. If the shoulder's bad that's an easy fix with a lathe.
 
#8 ·
As bizarre as it would be for a company that's been making barrels for as long and as well as Herstal has it sounds to me like your bore isn't straight. If my suspicion is correct no amount of chopping and threading will work. You can check this yourself with a micrometer by measuring the thickness from bore I.D. to barrel O.D. at the muzzle if it's off at all the barrel is the culprit. A barrel is threaded in a production capacity with an annular cutter followed by a die not a lathe and a die is self-centering therefore it's nearly impossible for the threads to be anything other than concentric with the barrels center. However, a barrel can be bored out of longitudinal alignment with it's true center axis. A micrometer will definitely confirm this.

Another potential issue could be the miniscule shoulder the SCAR's pencil barrel has. If the shoulder isn't completely square with the bore's center any muzzle device will skew under tension. For this you could check by simply screwing on the FH without contacting the shoulder then check with the rod. If the shoulder's bad that's an easy fix with a lathe.
That’s what I did. It looks off center still.

I hope the bore is not off. That would suck.
 
#10 ·
SCAR barrels initially have a bore drilled for the mandrel to fit into so it can be hammer forged...unless FN's mandrel is out of spec (which it could be)...I don't see how the barrel could out of centricity....sometimes chrome lining isn't concentric...which could happen...however you would be able to see that looking down the bore...

A barrel doesn't go "out of centricity" unless some really sever neglect has happened somehow...

If it isn't concentric now...it wasn't concentric to begin with...
 
#16 ·
The Surefire FH762K-SCAR-HC is for use with their pre SOCOM suppressors and I don't believe they will work with the 2013 and after SF SOCOM suppressors. I have two 2012 FA762K suppressors and this is the correct FH for them .
If you look at my rifle and the barrel assemblies you can see that no timing shims are needed and the flats on the
flash hiders are in different positions.
Air gun Trigger Machine gun Gun barrel Gun accessory
 
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#17 ·
The Surefire FH762K-SCAR-HC is for use with their pre SOCOM suppressors and I don't believe they will work with the 2013 and after SF SOCOM suppressors. I have two 2012 FA762K suppressors and this is the correct FH for them .
If you look at my rifle and the barrel assemblies you can see that no timing shims are needed and the flats on the
flash hiders are in different positions.
View attachment 149635
So they made it right the first time but now they don’t offer it. How annoying. I will try contacting Surefire again.
 
#18 ·
This could be your solution.
 
#22 ·
Who would any of you recommend to repair threads on a SCAR 17s barrel? I am actually thinking of just having it cut down to 14.5-15” and pin/weld the FH on as well.

To make a long story short, I use a Surefire FH and SOCOM 762 can. I had a very prominent smith install it. It is no longer concentric..
I had that ring on there and PMM installed it. It is no longer concentric with use.
@themao
Could you please clarify these statements so that everyone is on the same page.
Are you saying that your barrel was fine BEFORE, PMM did the install of the Surefire FH on your SCAR 17 barrel?
Also, if the above statement is true; Did you reach back out to PMM and let them know that your barrel now has a problem after they worked on it?
Thanks
 
#29 ·
Sorry for the late reply. I worked the past two weeks straight.

My can, barrel and flash hider are still at Surefire. Supposedly they are “done” but the rep has not given me any details.

I first installed the Surefire SOCOM 3 prong FH per Surefire’s instructions using their washer “reversed” as told my Surefire via phone and email back in 2014. This is before PMM made a ring or KBA. I used an appropriate torque wrench and Tangodown vise block.

After 2500 rounds, I saw loss of concentricity. I sent it to PMM with a KBA ring around 2018. He held onto it for 3-4 months with very little communication until I got it back. Only got to the range a few times (maybe 500 rounds max) until I noticed issues again.

No I have not contacted PMM again because they stopped taking barrels when I checked on their website. I guess they are now. Regardless, I will send it to Marvin Pitts who offered to take a crack at it if Surefire doesn’t help me. The shoulder is damaged for sure, but I need them to make sure my can and FH are ok as well.

I really don’t want to start a crap storm. I own a few other PMM items and have no beef with them. I think the issue is the SCAR 17’s lack of a shoulder for flash hiders that index to the shoulder and not the muzzle. DeadAir currently makes a SCAR specific FH that indexes to the muzzle. Using a crush washer like the Galil ACE is another solution. The issue is FN in my book, not PMM or Surefire.

I will post an update when I hear back from Surefire. Thanks
 
#30 ·
Surefire said my can is fine, flash hider may be "out of spec", but the barrel shoulder is definitely the primary issue.

They are looking into installing a Surefire FH set up to index off the muzzle, but he is waiting on special shims to do the job. That way, it would get around needing to machine the shoulder on the barrel.

I really hope they pull through with this. I don't understand why they don't offer flash hiders that index to the muzzle for rifles like the SCAR, AKs, Galils, etc. Pencil barrels are pencil barrels after all.
 
#31 ·
Surefire said my can is fine, flash hider may be "out of spec", but the barrel shoulder is definitely the primary issue.

They are looking into installing a Surefire FH set up to index off the muzzle, but he is waiting on special shims to do the job. That way, it would get around needing to machine the shoulder on the barrel.

I really hope they pull through with this. I don't understand why they don't offer flash hiders that index to the muzzle for rifles like the SCAR, AKs, Galils, etc. Pencil barrels are pencil barrels after all.
@themao
What's the name of the specific person that's going to do the Muzzle brake installation for you at Surefire?
 
#33 ·
I got my barrel and suppressor back from Surefire finally the first week of March. I reinstalled it onto my SCAR 17s and everything is now concentric. This is what they did:

1. SOCOM 762 can: For good measure, they replaced the attachment mechanism on the can saying it was worn. They did not explicitly say it was out of spec.

2. Barrel: The shoulder of the barrel that my should ring rested on was definitely deformed. Surefire at first used some muzzle shims (not should shims) in an attempt to time the flash hider to the muzzle rather than the shoulder of the barrel. I guess they have their own muzzle shim kit that they do not sell to the public. When they attempt this, the alignment was still off, so they had one of their machinists smooth out the muzzle of my barrel to make it flat again (they did not shorten it or rethread it). I had them go ahead and install a new Surefire SOCOM 3 prong flash hider onto my barrel complete with their muzzle shims, timed, red loctite, etc. It appears everything is good to go now after they did this. I will test fire the rifle at some point in the next few weeks, and I will ask my contact at Surefire if they can offer muzzle shims for Surefire flash hiders to the general public. It would be a great help to all of us who use Surefire adapters on AKs, SCARs and the like.

3. Flash hider: They replaced my 3 prong SOCOM flash hider with a new one for good measure. They did not say my old one was out of spec.

All of this cost me nothing. I guess that makes the price of a Surefire can worthwhile. I just hope Surefire starts offering muzzle devices for AK and SCAR users that need them timed to the muzzle end, not the shoulder of the barrel. I will be purchasing more Surefire suppressors in the future.
 
#34 ·
I got my barrel and suppressor back from Surefire finally the first week of March. I reinstalled it onto my SCAR 17s and everything is now concentric. This is what they did:

1. SOCOM 762 can: For good measure, they replaced the attachment mechanism on the can saying it was worn. They did not explicitly say it was out of spec.

2. Barrel: The shoulder of the barrel that my should ring rested on was definitely deformed. Surefire at first used some muzzle shims (not should shims) in an attempt to time the flash hider to the muzzle rather than the shoulder of the barrel. I guess they have their own muzzle shim kit that they do not sell to the public. When they attempt this, the alignment was still off, so they had one of their machinists smooth out the muzzle of my barrel to make it flat again (they did not shorten it or rethread it). I had them go ahead and install a new Surefire SOCOM 3 prong flash hider onto my barrel complete with their muzzle shims, timed, red loctite, etc. It appears everything is good to go now after they did this. I will test fire the rifle at some point in the next few weeks, and I will ask my contact at Surefire if they can offer muzzle shims for Surefire flash hiders to the general public. It would be a great help to all of us who use Surefire adapters on AKs, SCARs and the like.

3. Flash hider: They replaced my 3 prong SOCOM flash hider with a new one for good measure. They did not say my old one was out of spec.

All of this cost me nothing. I guess that makes the price of a Surefire can worthwhile. I just hope Surefire starts offering muzzle devices for AK and SCAR users that need them timed to the muzzle end, not the shoulder of the barrel. I will be purchasing more Surefire suppressors in the future.

@themao

Why did you let them use "Red Loctite" instead of Rocksett?
iirc "Red Loctite" is a permanent thing unlike Blue Loctite or Rocksett.
 
#38 ·
Took the SCAR 17 to the range two weeks ago. Everything is concentric, everything is running fine. Very smooth shooting suppressed (as it always was). I almost forgot how much I love my SCAR 17S.

Again, I think Surefire should offer the muzzle shims to the general public or at least to gunsmiths who know what they are doing. Otherwise, this gives the edge to Dead Air for offering Keymo flash hiders that index to the muzzle and not the shoulder of the barrel.
 
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