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View Full Version : How do manufacturers time barrels?


Scott S
June 12, 2002, 13:04
I'd swear I read somewhere that barrels threads are indexed to the flats. If that's the case, do manufacturers who assemble boatloads of FALs time barrels by indexing off the flats? I assume the folks and DSA and Entreprise aren't using the "two rods" method, though from what I hear, Century might.

Queenie
June 12, 2002, 13:43
I don't know how they do it, but I did notice on my G1 kit barrel there was a "witness mark" at the 6 o'clock position in front of the threads and a corresponding mark on the receiver stub.

rob1
June 12, 2002, 16:44
I recall a witness mark on my STG kit, but dont think there was one on my L1A1 or Imbel kits. Don't know how they did it, but I'm sure someone here has the answer.

kotengu
June 12, 2002, 19:18
The witness mark was put on AFTER they had barreled the upper, in order to more easily take THAT barrel off and put it back on again.

The Aussies used a fixture with a dial gauge. They recommend selecting a breeching washer that gives you a handtight of 15 from TDC, then torquing it down to 120 to 181 lbs with a hydraulic press. It's not quite clear from the manual (grainy pictures) what exactly the dial gauge is reading off of, but it looks to be part of the barrel.

They checked proper breeching by using a fixture, sight alignment gauge to check that the front sight was where it should be in realation to the rear sight and the rest of the gun.

HTH,

Matt

FWRA
June 12, 2002, 21:47
The gang at Liberty Arms in Texas (M-444 builders for IAI) developed a high tech 2 laser timeing system that allowed assembly to TDC within 30 seconds and it was spot on always. (as long as the gunsmith was paying attention.)
They built special fixtures for the process. The owner told me he spent about 2 grand designing and implementing it.

I guess when you are tooling up to build a thousand FALS it is a good idea to improvise a fast failsafe system. The guy really missed the mark though. He should have sold Century that system. :D

FWRA

Bruce Allen
June 12, 2002, 21:49
I was told by someone that the factories determined how much torque was required in pounds to put the barrel to TDC, and went with from then on.

Queenie
June 13, 2002, 00:16
Hmmm...the guy that barreled my 444 musta been pickin' his nose or something cause mine is overtimed. I have to crank the rear sight all the way left to center POI. :( Now I timed my G1 with the 2 rods, lined up the rear sight with the center mark on the lower and she shoots dead on. Never touched the sights again. :D Don't nee no steenkin' lazer beams........

BTW...just how TIGHT are those 444 barrels torqued in? I though about trying to re-time mine but I don't want to break my cheapo Columbian vise. :D

Uncle Buck
June 13, 2002, 11:14
Originally posted by Queenie
Now I timed my G1 with the 2 rods, lined up the rear sight with the center mark on the lower and she shoots dead on. Never touched the sights again. :D Don't nee no steenkin' lazer beams........



Exactly!

I see that the parallel rods method has been getting some bad mouthing here, but I have barreled dozens of actions using this method and it has always been dead on. I think that most of the problems have ben due to people not paying attention when they are using it.

The biggest potential for problems is not getting the front rod balanced in the gas block. You need to make sure that the hole is clean and free of burrs. Don't wedge the rod in the hole because you won't know if it is square. Just mark the center of the rod and balance it on the flat. The chances of this hole being drilled off square are slim to none and you have the same probability of the sight blade hole and the gas tube hole being drilled off square.

You need to sight down the center of the rods and look out to the tips of the rods. When you can only see 1 rod (the 2 are exactly superimposed) it is dead on. Depending on how good your eyes are, the method is good to 0.2 to 0.5 degree with 36 inch rods. This would be +/- 1-2.5 inches at 100 yards

It is the most accurate method you can use for under $2 and perfect for your average WECSOG gunsmith who doesn't need to invest hundreds of $$ in tools. If Century had been using this method, they wouldn't have had any trouble with timing.

W.E.G.
June 13, 2002, 11:34
You can be sure that the folks at Herstal used some ponderous one-of-a-kind contraption (or set of contraptions) to install barrels.

What Uncle Buck said for WECSOG'rs and two rods.

Still, I'll share a story about the vagaries of barreling. A MDFCA buddy showed up at my house with a spiffy-looking rifle that had been assembled by a well-respected gunsmith. My buddy reported that the rifle was shooting way out to one side. The rifle had been back to the 'smith for fixin'. After fixin' (replacement of the barrel no less!) the rifle was still shooting out to the same side.

My buddy was fed up with the shipping routine, so he asked me to WECSOG it right. We checked with two rods before messing with it. Everything looked good with the rods. We figured it need several degrees adjustment of timing to get the point of impact to center. We made the adjustment. Bad news is that now the gas piston was dragging badly. No good.

We admitted defeat, and returned the barrel back to its prior timing, resigned to it being a "scope gun." Well, my buddy took it back to the range and fired it with iron sights. WTF!!! right on the money. I would swear we did not change the timing. But, sure enough, it was "fixed." Don't ask me to explain. All I know is what happened and what happened.

I guess there is something to be said for the "take-it-apart-and-put-it-back-together" method of trouble-shooting.

gunhead
June 13, 2002, 22:14
For all we know, FN might have had Tooling or manufacturing flats/hex or watever that got turned off later on.
They might have first cut the thread to "P" point the shoulder. This can be easily checked with gages. Then the barrel screwed into a stationary block, against said shoulder & the flats & witness marks applied! Everything was done with Tooling gages designed by thier Methods Dept!
Usually, the trickiest part is done first then everything else is machined in relation to that. If you make the whole part then screw up the "P" point of the thread, it's Junk-City:p
Gages, gages & more Gages!
Very Interesting;)

Rule .308
June 14, 2002, 09:56
I generally use the "two rods" method for timing my barrels, but I also check them with a small level and the ever faithful "eyecrometers". All that being said I had an FAL a while back that, while being dead on with the two rods, was obviously far from being timed on a visual inspection. So I set her up so it was in compliance with my eye and the level and was overtimed a fair piece according to the two rod method. Took her to the range and it was about 2-3 clicks off of dead center at 100 yards. You can't ask for much better than that. The guy who built my original Fals (he's built about a million of everything that is military and semi auto) uses his eyecrometers exclusively. I have seen him have to re-do one barrel for an overtimed condition but by and large he gets them right everytime. His opinion is "once your eyes go it's time to hang it up anyhow". Something i have often wanted to build was a bolt carrier with two front sights set into it. If a guy could set the front sights into it absolutely dead nuts in line with each other I think it would be a simple matter of lining up the sight posts on the carrier(installed in receiver) and the front sight post in the gas block. It seems to me this would provide a fairly simple alignment process.