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PostPosted: Thu Oct 21, 2010 2:24 pm 
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Silent But Deadly
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So, I am looking to save some weight one of my guns. Is it safe to turn down an AR-15 barrel. I know they sell Lightweight barrels, and I could just buy one, but why? What profile could I safety turn down my barrel to? Are the lightweight barrels formed differently? Any ideas, suggestions?

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PostPosted: Thu Oct 21, 2010 2:48 pm 
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Silent But Deadly
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Sell the one you have and buy what you want. There is so much out there I wouldn't spend the money on having one turned down unless you can do it yourself or have a friend with a lathe.


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PostPosted: Thu Oct 21, 2010 2:59 pm 
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See below

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Last edited by goteron on Thu Oct 21, 2010 3:08 pm, edited 2 times in total.

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PostPosted: Thu Oct 21, 2010 3:04 pm 
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Silent But Deadly
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I have a lathe and can do it myself. its an ACR barrel, so no luck on getting a lightweight one yet without making an adapter and spending more money.

From research it looks like I can turn down the Gov Profile barrel this spec... Any reason why this is a bad idea?

http://www.ar15barrels.com/prod/lw.shtml

And then .6 in front of the gas block with a flare for the thread shoulder back to gov profile spec.

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PostPosted: Thu Oct 21, 2010 7:36 pm 
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Go ahead and do it. I had ADCO cut my 3 gun barrel down to the gvmt profile and like it a lot better. Turning it down had no effect on accuracy.


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PostPosted: Thu Oct 21, 2010 7:37 pm 
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Silent But Deadly
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I took a sec and pulled some rough dims off my colt lw barrel for you.

Image

The profile diameter goes down to .570 in front of the gas block and then flares out again to .610 to meet the crush washer.

Another idea I've been playing around with for one of my own barrels is fluting the .750 gas block journal to reduce weight.


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PostPosted: Thu Oct 21, 2010 8:05 pm 
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Silent But Deadly
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Gunsmith, thanks so much for the help. I'm going to profile just like that. Any issues you see with that??? Thanks again!

Can I go down to .625 behind the GB?

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PostPosted: Thu Oct 21, 2010 9:19 pm 
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Silent But Deadly
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If you can cut a taper with your lathe I'd suggest mimicking the Colt spec. If you can't, you can always induce a taper by offsetting your tailstock and turning between centers. However if you change the .668 to a .625 you're only changing your wall thickness by .021 leaving a .2005 wall, which should be safe; I've heard of people going as low as .600 near the throat. Definitely consider fluting the gas block journal as you'll be removing a substantial amount of material. Just stop the flutes where there are pins and at the gas port and you'll be golden. Let us all know what weight you get the barrel down to!


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PostPosted: Fri Oct 22, 2010 11:49 am 
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Silent But Deadly
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Gunsmith, I put it all in CAD, By going to a lighweight barrel, I am only saving about 4 ounces... If I flute the journal, I get another ounce. Granted thats all weight up front, but I was hoping for something more substantial. I am doing something wrong here?

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PostPosted: Fri Oct 22, 2010 10:42 pm 
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No you're not doing anything wrong and this is the problem that the ACR team is encountering right now. That being said, honestly I can't tell you if you're going to notice the difference of a 1/3 of a lb up front on your particular gun. Seeing as an ACR is relatively muzzle heavy, it very well might make a big difference in how it handles.


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PostPosted: Sun Oct 24, 2010 12:07 am 
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Silent But Deadly
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Instead of trying to retrofit an AR-15 barrel, I decided to reprofile mine. I have a crappy lathe and am and even worse machinist.

Starting weight of barrel alone was 24.9 ounces, after the weight reduction it was 22.1. Not as much as I had hoped.

Keep in mind I already lost 2-3 ounces by chopping from 16.5 to 14.5

Some other weights

Gasblock - 3.75
Piston system - 4.55
Barrel nut - 2.4

The gasport size as best as I can tell is .052

So, in total I've lost 5-6 ounces out front, the CG of the barrel is further back. It shouldnt affect accuracy or reliability.

I am going to shave another few ounces by mounting my 620v directly to the rail and have a few other ideas as well.

Does anyone know the weight of a factory 14.5" lightweight?

I could probably get another .5 ounce if I really tried, but my lathe sucks, so it's slow going.

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