Has anybody ever successfully removed the FN 3 Prong Flash Hider from a SBR barrel (10" or 14") barrel.

I have a factory 10" barrel that I have been trying to get the hider off of without success to install  an AAC 51t mount.

I have it in a barrel clamp in a vice, heated the hell out of it, and have even used a 3ft cheater bar on the wrench to no avail.  It seems like you would twist the barrel into a pretzel before that hider would budge.

Everything I have read says its threaded 1/2x28 tpi RH (so lefty-loosey / counter-clockwise when looking down the muzzle just like an AR)

Is there a pin I am not seeing or does FN weld the hider on somehow.

Barrel looks like this



I am just about down to cutting it off at this point but prior to destroying the factory hider I am curious if anybody has come across and solved this issue on these factory SBR barrels.

*edited to add, it is brand new out of the box, so there should be zero carbon fouling

I had no trouble removing mine with a standard combination wrench (replaced with a KAC M4QD comp for my pending QDSS-NT4).

I do, however, have the TangoDown SCAR vice block set which is a must for any SCAR muzzle device work. But it sounds like you have a vice block, too.

I'm sorry to hear you're having problems with it.

Submerg the flash hider in water over night. FN might have used rocksett. Then in morning should just come right off with no heat.

Rocksett is water soluble don't use heat it gets harder to come off. Rocksett will withstand temp up to 2,000 degrees.

I have never had rocksett provide this much strength before.

I did end up boiling it in water for 20 minutes last night without any positive effect.

Going to try and get it off again this evening.  If that doesnt work it will go off for professional assistance.

I didn't do it myself but had my local gunsmith remove the one on my exact same barrel and replace it with a 51T AAC brake last weekend.  

Dropped it off and picked it up a few hours later.  He didn't mention having any trouble getting it off.

Well I finally got the flash hider off last night.

Ended up having to make a custom barrel clamp for my vice that was "tapered" to match the taper of the SCAR barrel, so I could get 100% contact metal to metal contact along the length of the barrel.  My wooden barrel blocks that have "give" to them to accommodate tapered barrels couldn't get tight enough and with enough heat on the flash hider would start to burn.  Straight vice barrel clamps couldn't get a good grip given the taper on the barrel.  Maybe aluminum ones would

I had soaked in in water overnight so I  put it in the vice with the custom clamps and used a 3ft cheaper bar to tighten the vice down as hand tight still was not tight enough.  (barrel would break free of the clamps)

Figured well lets try heat again.  Used up almost an entire canister of MAPP gas to get the entire flash hider glowing red, cranked the vice even tighter, wrench + 3ft cheater bar and it finally popped loose.

I don't know what type of thread locker FN uses or how much torque they put on the hider at the factory but I have never come across a flash hider in almost 20 years of amateur gunsmithing that was so difficult to remove.  

FYI I also called FN to ask what the hell they use and they were decidedly unhelpful.  Tech on the phone couldn't even confirm RH vs. LH pitch.  Best I got was "yeah I think they use threadlocker".

I don't think they use threadlocker. Every SCAR barrel I have deal with has clean threads under the hider. That one must have been torqued like crazy, or your blocks weren't giving good purchase on the barrel.

The SCAR-specific barrel vice blocks actually clamp around the front sight and gas block.

Yep, the TangoDown blocks worked without a hitch, was more than 35ft/lb and less than 50ft/lb to take off the flash hider.

Wow I bet it felt good to get that flash hider off.

Very glad when I finally got it to break loose.

I thought about using the gas block to keep the barrel from rotating in the vice. I even modded my wooden barrel vice blocks to grab the gas block but watched how much the gas block flexed once pressure was put on it and was concerned about oblonging the pin/hole on the gas block to barrel interface or warping the tube on the block.  The SCAR only had one pin vs. an AR which has two so I suspect it wouldn't take much to screw up the barrel to block interface.

Given how much torque it required to get off I was concerned that if I ultimately used the gas block to keep the barrel from rotating in the vice I would have damaged the block, barrel, or both.  I considered buying the Tango Down block set, however it was made out of plastic and figured it would melt before I even got it hot enough to get the flash hider off.

I don't know what the foot pounds were required to remove it off but I am pretty confident  that I could have done pull ups on the 1ft long wrench handle without the flash hider breaking loose.  I weight 220 and had probably had a quarter of my body weight hanging from a ~3ft long square tube over the wrench handle before it popped loose and that was after I put almost a whole bottle of MAP into it.  

I don't know what the F*%$ FN did when they torqued that hider on but it was excessive.  My hands still hurt 24 hours later from pulling on the vice handle trying to keep the barrel from rotating.

Some pics of the excursion

Setup  right after it came loose



Tapered Vice Blocks


Finally with AAC Mount

Do you need to remove the bottom rail section from the barrel to sue the TangoDown blocks?

No, but you will need to remove anything attached to the bottom rail.

Stephen