How do I index a combo device?

[ratas calientes]

In preparation for some black-rifle builds this next September, particularly my para build, I am chopping a barrel to 18 inches, and threading it for a Belgian combo device. What I don't understand is how the combo device indexes on the threads. Does it seat against the muzzle, or the back of the thread relief? And what is the best way to get it to index properly? Do folks make shims, or do I need to keep shaving the muzzle till it tightens to the correct spot?

Any advice is appreciated, of course.

[shoota1911]

OK first off, the holes index at 45 degrees, the reason for this is that if indexed at 90 degrees, the muzzle blast throws up a lot of dust when shooting from prone position. As far as getting to tighten in this position, I have a drill that just clears the tops of the threads, that is sharpened with a flat point, just like a 2 flute end mill. I chose the drill over an endmill, because an endmill would more than likely damage the threads more than the drill would. Then it was just a cut and try deal, little at a time, till the combo devise timed at 45 degrees with reasonable torque, so in my case it is bottoming out on the muzzle. I then blind pinned it with a cross pin which is not drilled all the way through. I don't like the idea of a blind pin drilled straight into the side of the barrel and then held in place with a weld . I have NO evidence to suport my theory about silver solder but I will air it for what its worth, I really don't like the idea of putting a torch on the end of the barrel and getting it hot enough to flow the solder, this will definitely do weird things to the barrel. Whether the weird things show up as a lack of acuracy or whatever or nothing I don't know.... just a feeling. When I was building IPSC .45s I always secured the compensators with High Temp Locktight, never a problem, but I did see some silver soldered ones snap off, I guess due to the barrel getting too hard and brittel from the heat from the torch. OK so you can probably normalise/aneal the end of the barrel, but in order to do all this high tech stuff you need to know exactly what steel the barrel is made from. Any ideas?? I would bet 4140 chrome molly for openers....

[xIA]

Here ya' go:

From:
http://www.falfiles.com/forums/showthread.php?s=&threadid=96763&highlight=.020


The notch at the back of the FH should be at BDC.

Cut-and-Paste from an earlier post:

You will often see earlier FALs w/ the short Combo Device with a small crosspin at the base to keep them (RH thread) from unscrewing. These are on guns that were cut for the Long FH (and threaded RH), to replace them after they split. Eventually, the importer started doing it prior to shipment to alleviate the problem. This from the importer's own gunsmith directly. They even had "Retrofit Kits" that came w/ the pin, Combo Device and .005, .010 and .020 shims to index them correctly.

Edit to add:
Can't quote a source on this one, but IIRC the problem really started on the Type III guns after FN started using "Powdered Metal"
technology to produce the FHs...


I'll add that .042 would equal roughly one full turn, so the shims individually or in combination would correct any indexing issue.

[elbo]

http://www.dsarms.com/item-detail.cfm?ID=002W&storeid=1&image= I have several in anticipation.

[ratas calientes]

Thanks for your help. :cool:

[GT]

Ratas,

I too am preparing for next September. This is what I did to index a short combination muzzle device.

I filed the end of the muzzle a little bit at a time, using a square to ensure I kept the muzzle square. I did this by trial an error until I got is set up so the muzzle device will be indexed properly with a good amount of touque. I used a thin wrench, 18 or 19 MM, I can't remember which, to tighten the device. Then I crowned the muzzle in the usual fashion, which I do on every build anyway. After I parkerized the barrel and muzzle device seperately, the muzzle device tightens on securely and indexes fine. Now I don't have to worry about loosing shims if I want to remove the device for some reason.

Gary

[W.E.G.]

Originally posted by shoota1911
I have NO evidence to suport my theory about silver solder but I will air it for what its worth, I really don't like the idea of putting a torch on the end of the barrel and getting it hot enough to flow the solder, this will definitely do weird things to the barrel. Whether the weird things show up as a lack of acuracy or whatever or nothing I don't know.... just a feeling.

There is ZERO evidence to support the idea that any harm is done to the metallurgy of the barrel by heating it to 1200 degrees. Sometimes, the process of heating the metal draws oil and/or fouling out of the small grooves and/or pores of the metal, causing a "dark spot" of gunk near where it was heated. Depending on the quantity of gunk, and extent of oxidation of gunk, the "dark spot" may look really nasty. After firing a couple boxes of ammo, and cleaning, the "dark spot" always disappears.

Welding or drilling the barrel is a horse of a differnt color. Those processes actually move or re-move metal. You better really know what you are doing when you start one of those jobs. Otherwise, something does get damaged. And of course, it does no good for accuracy if the solder runs into the muzzle of the rifle during the soldering process.

But, lets not get started with the idea that soldering a muzzle-thingy or a barrel-band on a rifle barrel does something bad to the metal. There is simply NO EVIDENCE to support that speculation.

I'm all in favor of folks putting the original muzzle devices on their FAL's. Just remember, those muzzle devices were NOT designed as accuracy enhancers, or recoil reducers.