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Old May 04, 2015, 17:34   #1
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Barrel Overtiming Logic, Math, and Reality Check

I have a barrel and receiver which is overtiming with little torque by approximately 3 degrees. It hand times to past the “golden triangle.” So I need a little math, and logic behind my math, check please. Here is what I have:

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An FAL barrel is threaded 16 TPI so one turn equals 0.0625 inches. Therefore, 0.0625 inches = 360 degrees. Leading to 1 degree = 0.0625”/360 degrees = 0.0001736 inches per degree. So for each (x) degrees a barrel overtimes you would need a shim (x)*0.0001736 inches thick. If I want this barrel to hand time at 11:30 and knowing that one hour is equal to 60 minutes or 30 degrees. I would want a shim 15 degrees * 0.0001736 inches = 0.002 inches thick.

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Does this compute and where can I find this thin of shim stock. I think a Coke can is .005 inches thick?


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Old May 04, 2015, 17:45   #2
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center punch time
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Old May 04, 2015, 18:21   #3
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Shim stock.
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Old May 04, 2015, 18:33   #4
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http://store.louzampini.com/product-p/90751137a2.htm


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Old May 04, 2015, 18:50   #5
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Thanks guys... Hahaa, Google is my friend...

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Old May 04, 2015, 18:57   #6
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Beer can, compass, pair of scissors.
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Old May 04, 2015, 18:59   #7
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Quote:
Originally Posted by meltblown View Post
Beer can, compass, pair of scissors.
I cut out some coke cans like that but I am a little leary of using aluminum on steel application. Not sure if that is a legitimate concern or not......

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Old May 04, 2015, 19:13   #8
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It's going to squish down to the point it's pretty solid. Hell people silver solder FHs on and they don't move. I didn't really like the Indian motorcycle grip spacers cause the ID is a little big and doesn't contact the inner shoulder. But still not a bad way to go.
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Old May 04, 2015, 20:52   #9
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Quote:
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It's going to squish down to the point it's pretty solid. Hell people silver solder FHs on and they don't move. I didn't really like the Indian motorcycle grip spacers cause the ID is a little big and doesn't contact the inner shoulder. But still not a bad way to go.
I was more concerned about galvanic corrosion when two dissimilar metals are in contact with one another. Not sure if that would be a big issue with a rifle but if the aluminum breaks down I could foresee the barrel loosening...maybe that is just my anal retentive scientist cynicism showing...

I also have some of the Indian throttle spacers. The smallest one that have is too thick for my application and like you note the inside diameter is a little to large. Good inexpensive idea but just hasn't worked for me yet...

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Old May 04, 2015, 20:58   #10
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Quote:
Originally Posted by meltblown View Post
Beer can, compass, pair of scissors.
Quote:
Originally Posted by G3isMe View Post
I cut out some coke cans like that but I am a little leary of using aluminum on steel application. Not sure if that is a legitimate concern or not......

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The Coke can mod works fine.
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Old May 04, 2015, 21:36   #11
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Shim stock.******** ***************** ***************************************** width="1" height="1">
That's exactly what I use. Works as advertised.
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Old May 04, 2015, 23:05   #12
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When I had that problem I got a shim from Brad a Gunthings. He still has them at 7 bucks a pop.
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Old May 05, 2015, 08:55   #13
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Both Brad's and Jerry Greer's are ok, but not exactly right.

Any tool and die makers out there? How hard would it be to make a stamping die to cut 1.0 ID and 1.2 OD from shim stock?

Optimal increments would be .0005", but realistically, I'd probably have to go in .0020" increments.
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Old May 05, 2015, 09:06   #14
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Rather than fiddle with super thin shim stock, get access to a lathe and mount up a roller bearing in the toolpost and bump the edge of the barrel shoulder to push it back some. Then be very carefull when re installing the barrel do not overtime at all, but should give you enough tension to time up right.
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Old May 05, 2015, 09:15   #15
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Quote:
Originally Posted by akajun View Post
Rather than fiddle with super thin shim stock, get access to a lathe and mount up a roller bearing in the toolpost and bump the edge of the barrel shoulder to push it back some. Then be very carefull when re installing the barrel do not overtime at all, but should give you enough tension to time up right.

Sometimes works if you're getting to TDC with as little as 80 ft pounds, and 100 ft pounds pushes you over.

But it's sub-optimal.

Another alternative is to turn the shoulder back another .050" and use standard L1A1 breeching washers. Will have to cut a clearance for the carry handle screw (or use L1A1), and remove the flats from inside the handguard support.
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Old May 05, 2015, 10:28   #16
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All kinds of shims here:
http://www.mcmaster.com/#standard-shims/=x1sfyb
OD looks too large though on the ones with 1.0-inch ID. Could trim down the OD easily enough. Grainger also has shims.

Or get a punch tool set. Here is a cheap one:
http://www.harborfreight.com/9-piece...set-95547.html
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Old May 05, 2015, 20:12   #17
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Another alternative is to turn the shoulder back another .050" and use standard L1A1 breeching washers. Will have to cut a clearance for the carry handle screw (or use L1A1), and remove the flats from inside the handguard support.
This is what I was thinking and how I'd handle it.
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Old May 05, 2015, 20:42   #18
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www.gunthings.com has shims in .002", .005" and .015" thickness for $7 ea. Get a .005 which should put you back to 11:00 or so and torque it to TDC.
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Old May 05, 2015, 23:00   #19
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ratas posted a link for this vendor. They sell round shims with 1" ID and 1.5" OD. The various thickness's are in 0.001" increments from 0.001" to 0.012". They sell them in packs of 10 shims and the price ranges from $7.28 to $5.09 per 10 pack. If I can not find something local, I think I am going to go this route and buy a 10 pack of 0.002" shims.

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Old May 07, 2015, 16:10   #20
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Quote:
Originally Posted by akajun View Post
Rather than fiddle with super thin shim stock, get access to a lathe and mount up a roller bearing in the toolpost and bump the edge of the barrel shoulder to push it back some. Then be very carefull when re installing the barrel do not overtime at all, but should give you enough tension to time up right.
A similar idea might be to flip a HSS bit in the toolholder and press it in to the bbl shoulder while spinning in the lathe. This will result in two displaced ridges, but at least they will be symmetric in height and around the bore.

I may try this next time. I have cut really small shims on the lathe before, tedious, and it is a pain twisting them down the threads.
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Old May 07, 2015, 18:59   #21
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When I'm cutting for a breeching washer, I leave a 1.0" shoulder so the washer stays centered.
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Old May 07, 2015, 19:59   #22
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Its been some time, but 1966 VW beetle, kingpin shim packs may work.
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Old May 09, 2015, 22:12   #23
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Quote:
Originally Posted by G3isMe View Post
ratas posted a link for this vendor. They sell round shims with 1" ID and 1.5" OD. The various thickness's are in 0.001" increments from 0.001" to 0.012". They sell them in packs of 10 shims and the price ranges from $7.28 to $5.09 per 10 pack. If I can not find something local, I think I am going to go this route and buy a 10 pack of 0.002" shims.

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Unless you are in a hurry, I would ask you to chill a bit until I can get out to the shop. I think that I may have what you need collecting dust in my box o FAL.

ETA: STONEY gave you a good remedy. If you don't understand what he means, I'll give you a tutorial via PM after I get to the shop tomorrow.
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Old May 10, 2015, 04:27   #24
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Or you can just use your math which is correct and retime a full revolution and cut chamber deeper, did this on a heavy barrel recently. Assuming not chromed and will have to trim piston a little.
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Old February 18, 2018, 19:14   #25
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Or you can just use your math which is correct and retime a full revolution and cut chamber deeper, did this on a heavy barrel recently. Assuming not chromed and will have to trim piston a little.
As usual, this is very stupid advise. And as usual, you're probably lying. Because now your handguard screw won't fit and the gas piston will not have the correct gap to the front of the bolt carrier.
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Old February 18, 2018, 19:18   #26
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As usual, this is very stupid advise. And as usual, you're probably lying. Because now your handguard screw won't fit and the gas piston will not have the correct gap to the front of the bolt carrier.
Could be why there are chamfer issues on the ones that people are seeing from France and other places
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Old February 18, 2018, 20:00   #27
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2015 thread? How did this work out for you G3?

I'm assuming the build is complete by now.
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Old February 19, 2018, 02:02   #28
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2015 thread? How did this work out for you G3?

I'm assuming the build is complete by now.
It worked fine. Build completed and on to the next one. I bought a roll of 0.003" shim stock and cut one if/when I need it. I have been lucky as this thickness has worked for me in all of the overtimed issues I have experienced since I bought the shim stock. Sometimes a little more or less torque is required when seating the barrel...

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