Turning down ar barrel?

[dmcmillenfv]

First off I am a machinist by trade, and I have a 20in hbar barrel on one of my ar's. I hunt coyotes with this gun, but it's a bit heavy. Has anyone turned down the profile on a barrel before, and not have any change in accuracy. I know repeated fire will heat the barrel up and loose accuracy, but I'm more interested in 1-3 shot accuracy. I'm not sure if turning the barrel will release stress in the material, (its chromolly) causing accuracy problems. The gun is a tack driver now and I don't want that to change.

[wash]

I know it can be done but I don't know exactly how to do it.

20" is pretty long so maybe a combination of a dead center, lathe dog, steady rest and follow rest is what you need?

In my opinion, if you have a good shooting barrel, don't risk it. Buy a lighter profile barrel and put together another upper.

If you are a good shopper, the new upper will be pretty cheap and when you deduct the cost of a professional re-profile job, it will be a great bargain.

If you are buying new, a 16" mid-length will weigh less or have a much more rigid barrel depending on profile. If you can live with a bit less velocity, that might be more accurate at short to medium range.

[Richard Erichsen]

First off I am a machinist by trade, and I have a 20in hbar barrel on one of my ar's. I hunt coyotes with this gun, but it's a bit heavy. Has anyone turned down the profile on a barrel before, and not have any change in accuracy. I know repeated fire will heat the barrel up and loose accuracy, but I'm more interested in 1-3 shot accuracy. I'm not sure if turning the barrel will release stress in the material, (its chromolly) causing accuracy problems. The gun is a tack driver now and I don't want that to change.

Given the relatively low cost of barrels, why risk ruining a "good one" for target use? If you aren't roaming around on an ATV, a heavy rifle would start to suck, especially in rough terrain, so understand your rationale.

You can save weight in two ways (restricted to the barrel) - length and diameter. You could go down to a thinner diameter and if you reduce the length, the rigidity could remain the same, or fairly similar. I'd suggest contemplating dropping to 16" in addition to taking down the diameter to near pencil proportions, or even just M16/AR15A1 diameter. That should do it. Dropping weight by choosing lighter furniture helps, polymer 10 round mags are obviously lighter than 30 round steel, if you have them.

R

[kcstott]

I've never heard of someone saying the AR was a heavy rifle.
Not even with a lead lower.

The trick to turing down a barrel without inducing stress is to keep it cool and use sharp tools.
But even on an H bar you will not save much in terms of weight. And you will stand a good chance of fouling up the accuracy.
Get a different barrel and sell the one you have or just buy a different upper.

[dmcmillenfv]

I've never heard of someone saying the AR was a heavy rifle.
Not even with a lead lower.

The trick to turing down a barrel without inducing stress is to keep it cool and use sharp tools.
But even on an H bar you will not save much in terms of weight. And you will stand a good chance of fouling up the accuracy.
Get a different barrel and sell the one you have or just buy a different upper.

Screwing up the barrel is what I'm afraid of. The only problem about swapping barrels is nobody I've seen (shien, krieger, hart) make lightweight contour 18-20in barrels.. I don't want to use a 16in, I already have a carbine. I guess the next thing I can do is swap out my magpul prs stock, but I love that stock.

[kendog4570]

Turn it slow and easy and it will be fine. If it is quality it probably still will be. Garbage in-garbage out sort of thing. If you are really worried about it, grind it.

[CIV Tactical]

Another option is fluting it. If you do turn it down you will have to make a custom dead center to clear the extension lugs. hope this helps.

[kcstott]

The question is how much weight are you trying to lose?? Not you the rifle.

[kendog4570]

Another option is fluting it. If you do turn it down you will have to make a custom dead center to clear the extension lugs. hope this helps.

Hold it in a collet?

Hell, a 3 jaw is fine for profiling.
Or a dead center bearing on the extension approach angle, and a lathe dog??

There are many ways to skin this cat.

[wash]

I've read that a 20" WOA DCM profile barrel weighs 3.4 lbs.

If you look here: http://www.ar15performance.com/5_56_223

They have a 20" that weighs 2.75 lbs for a 0.65 lb savings.

Their light weight 16" weighs 1 lb, 9oz for a further savings of 1 lb, 3 oz over the 20" barrel.

The medium weight 16" weighs 2 lbs, 2 oz.

Any of those should make a nice rifle.

[CIV Tactical]

Kendog that is true. I just made myself a dead center for the three jaw that clears the lugs and sits in the chamber. a lathe dog then I turn down between centers. Easy enough I guess.

[ILVSMOG]

I had a discussion about this same thing with a machinist once. He used to profile the barrels for Calico way back when. He told me that besides just turning the barrel, there was a calculation required to account for the flex in the barrel as the tooling moved across it. Based on his description, I'm not sure it's something you could accurately do for a one-off like you're talking about.

[kcstott]

I had a discussion about this same thing with a machinist once. He used to profile the barrels for Calico way back when. He told me that besides just turning the barrel, there was a calculation required to account for the flex in the barrel as the tooling moved across it. Based on his description, I'm not sure it's something you could accurately do for a one-off like you're talking about.

That may be true for a few different types and materials of barrels but that won't hold true for a barrel of unknown make up and hardness.
Taking .020" of a .920" diameter bbl will get you near a third pound in weight savings. So if you took .040" over all you'd be near a half pound. And .040" is not that much nor would it be hard to do in light multi pass cuts.

I'm not suggesting anyone actually do this because I feel a half pound in weight savings is a waste of time. That said if your three jaw runs true enough then just chuck up on it, live center on the other end and if needed a follow rest at the carriage. Take light cuts, use a water based coolant, and take your time.

Personally I'd get a 16" barrel as you won't loose much in velocity. What's 150 fps anyway? They animal is not going to care.

[Richard Erichsen]

Personally I'd get a 16" barrel as you won't loose much in velocity. What's 150 fps anyway? They animal is not going to care.

I agree with that. If you want light AND simple, a 16" barrel loses only very little in velocity, not enough to worry about. M4 barrels are shorter still and they are obviously still quite deadly on two legged critters.

R

[uxo2]

ADCO