If you want to get the most accuracy out  of your barrels you should not tighten a crush washer more than a1/4 turn to index a muzzle device. If you have to go  a 1/2 turn or more to index ,you should  remove material from the washer. You can do this with a fine cut flat file or some emery paper on a hard flat surface.  just remove enough (from the concave side)to get you  within a 1/4 turn to index.  Try and keep the washer as parallel as possible. I happen to be able to do mine on a surface grinder in my shop. I build about 15 to 20 service rifles a year , many of which go to camp Perry and shoot out to a 1000 yds. When a customer requests an A-2 birdcage on his rifle  it get machined so  it indexes by  hand to the 12 o,clock posistion  and is held in place with Loc- tite. One  of the key elements in  making  an AR shoot is keeping the barrel STRESS FREE. On a tacticle AR a 1/4 turn  is fine  and will keep your brake/ hider from shooting loose.   PATRIOT ARMORY    CLASS 07 MANUFACTURER

I had been thinking about the same thing.  About the only good thing to come out of the AWB was to get rid of flash suppressors on match rifles.  With the exception of a barrel tensioner or counter weight (whip reduction), anything hanging on the barrel's end reduces accuracy.

I have found that using a peel washer works best for flash suppressor indexing.  Peel washers cost more, but, for me, I find them easier to work with.

Are there any National Match modifications to the A2 flash suppressor, such as reaming the inside to a larger diameter?  I use a #7 reamer (I think) to open the flash suppressor on an M14.  The standard M14 flash suppressor will hold water; when water gets in there, it throws the bullet anywhere but where you are aiming.

I have found that crude accumulates on the muzzle when using a muzzle device.  I figure that it blows off when enough gets in there, but it would sure be nice to have a muzzle device that cleaned itself with each shot, just like not having anything there.
Crude at the flash suppressor

Just a couple of questions.
1. Is it better to just skip the washer ?
2. How about loosely indexing & using Loctite to secure the FH on the barrel ?
3. Will someone shooting a service grade rifle notice an accuracy improvement ?

Factory threaded barrels are not threaded all the way to the barrel shoulder because of the single point threading tool used to cut the threads. Almost all FH will bottom out on the unthreaded  portion  of the barrel leaving about a .062 gap. So you need some kind of (washer) to fill the gap and to achieve proper index.  What i do when building a rifle to shoot N.R.A. high power, (service rifle class) is to  remove the first couple of threads inside the FH and then machine the back of the FH to achieve proper index when tightened by hand , Loc -tite does the rest.   By removing stress  and or constriction at the muzzle  you would see  an improvement in group size at 200 yds and beyond. Of cource you must take into consideration barrel  and ammo quality etc.    hope this helps.                PATRIOT ARMORY .

That sounds like a bit of work.  That's is why I like nothing on the end of my match barrels.  Of course, I can't get away with that with a M1A.

BTW, do you know any books that show how to accurize the AR15?  I mainly have several questions about building a straight shooting upper.

The  n.m. mod for the A-2 FH  is to open up  the area ahead of the muzzle to eliminate that  '' pocket'' that traps all that  crud .   this mod . helps to eliminate turbulance inside the FH as the bullet passes thru.  Idont remember the exact dimension  but its a straight cut done with a boring bar in the lathe.   I have made some FH that were bored straight thru  (with no  crud pocket )  they have the A-2 profile but with slots cut like the old STONER style.  They work great , easy to clean.  All made from tool steel ( A-2 )  heat treated  , tempered to  45-50  Rc then parkerized.     (mang. phos.)    Hope the info helps!     PATRIOT ARMORY

I figured that it had to be something like that.  I'd like to know the cost of one.  I have a WOA SPR upper with a standard A2 flash suppressor.  It shoots GREAT as it is.  If I can make it shoot better, then I am all for it.

A great book for the AR is  The complete guide to AR-15 accuracy by Derrick Martin& Barrett Tillman. To build a good shooting  AR upper is pretty simple  #1  get a good barrel (not chrome lined)  #2   you want the barrel extension to fit the upper snugly (not to tight ,you dont want stress in the upper) #3 float the barrel.#4 lose the FSB taper pins  ( use set screws) . and last but not least a  solid ,repeatable rear sight.         PATRIOT ARMORY.    

Fulton Armory has them N.M. A-2 FH  $14.95

Quoted: A great book for the AR is  The complete guide to AR-15 accuracy by Derrick Martin& Barrett Tillman. To build a good shooting  AR upper is pretty simple  #1  get a good barrel (not chrome lined)  #2   you want the barrel extension to fit the upper snugly (not to tight ,you dont want stress in the upper) #3 float the barrel.#4 lose the FSB taper pins  ( use set screws) . and last but not least a  solid ,repeatable rear sight.         PATRIOT ARMORY.

Now you have me really curious... as it seems silly NOT to do these things.  I'm building a 16" right now, and although it's not going to be bench gun, the more accurate the better.

I want to ask, what is the philosophy behind using set screws as opposed to pins for the FSB???


You talk about just a quarter turn on a crush washer.  I assum there is a certain torque limit where you see effects on accuracy, do you happen to know what it is?

I"ll have to keep these things in mind.  Good info!  Appreciate it a lot.

Gundraw

Why not jus use PEEL WASHERS. ya get the same effect without the hassles?

Easier to just use an A1 birdcage, chuck it up and ream it out with a 1/2 " or so drill bit , throw a full peel washer / or lock washer on and hand tight it  & loc-tite. No index to worry about.

There is nothing wrong with an A-1 style FH  for a tacticle rifle or  "bench" rifle  , but  for a compitition rifle   (N.R.A. HIGH POWER) the A-2 is prefered over the A-1 ,  and here is why,   when one of your shooting posistions is rapid fire prone at 300 yds. the last thing you want is dust& grass and whatever else is in front of you getting kicked up and obscuring your sight picture of  an already small target. PATRIOT ARMORY

   It all goes back to taking as much stress off the barrel as possible. The FSB taper pins are basically a wedge, this wedge will impart radial stresses into the barrel(as little as it might be it is still stress) and can effect accuracy at long range. By using set screws  you can adjust the FSB for windage, snug up the set screws and  apply some 290 Loc-Tite in between  the FSB and the barrel, and have pretty much a stress free FSB.   You can drill& tap the taper pin holes 8-32 or just tap the hole in between the ears for the front sling swivel  10-32.    hope this clears things up.  PATRIOT  ARMORY