Tensioned barrel AR lite - Page 1

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[ARCHIVED THREAD] - Tensioned barrel AR lite

Posted: 10/1/2015 6:51:14 PM EDT

Good afternoon guys,
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Buddy of mine thought I should document this process, so here
goes.
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Disclaimer: I am neither a writer nor a machinist, but know enough
about both to get myself into trouble.
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Intro:

I conceived of this idea a while back, and over the last 2 years
have done my best to make it a reality. What you see below is the proof of
concept, which is my tensioned barrel Mauser (VZ24). It’s not an AR15, I’m aware.
I smithed this gun first because the bolt action rifle is a lot easier to work
on than AR15 (I thought). I will do this same work to an AR-15 below. As of
today I’m 80% done.
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First things first, I bought a new barrel for my Mauser. This is actually
what kicked off this entire project. I believe I ordered a varmint weight
barrel, but what I got was a .270 WIN sporter contour. This of course is what
happens when you order gun parts while enjoying Makers Mark. Now I love the
.270 and I wanted to make it work, so I decided that to combat the whippyness
of the sporter contoured barrel I would tension it inside a thin walled carbon
fiber tube. I went to work and put the barrel on the lathe before it was in the
action. I cut the shoulder down to accept the friendly end of the tube, and
threaded the enemy end of the barrel to ½-28. Then I bought a reamer and a box
of Barnes solid copper ammo to headspace the barrel. Turns out it was actually
chambered too deep, and the bullet flew in like a hot dog down a hallway. I returned
the barrel reamer (there went 50$) and proceeded to stone the face of the barrel
and the face of the action until the bullet fit just ever so snug. This took
forever, I would not suggest you do this, wait till Monday and use the lathe at
work. It took friggin 8 hours and a ½ bottle of eagle creek I was saving for something
more fun and less tedious, like trimming my toenails, or almost anything else.

That done I got the barrel in the action and torqued it down,
which of course broke my action wrench. Fortunately those Barnes and everything
else I’ve put in that gun fit spectacularly, seeing as I won’t be getting the
barrel off until I make another action wrench. I had it all cerakoted by a
buddy, and started working on fitting the stock. First step was to remove a
bunch of wood from forward of the lug. this was when my buddy told me to start taking pictures.

Posted: 10/1/2015 5:46:09 PM EDT

[#1]

Free floating a barrel takes a lot of putting the action in and
out, so i'll spare you the details.
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Highlight: it’s not a tedious as stoning a barrel to fit.

Lowlight: when you get a splinter you got to wonder what’s in that
old Czech cosmoline, I mean that cows been dead a long time.
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In this pic you can see the shoulder I cut on the barrel. The
location was dictated by the carbon fiber tube, which has and OD of .883 and an
ID of .8125.

Now I had to remove enough wood for the carbon fiber tube to
free float the entire assembly. I used heavy grit sandpaper wrapped around something
with a convenient OD. Once that had enough clearance I threw in the goop. I use
Devcon for all my goop needs, although this was my first time using alumabed
instead of steel bed. I think I like the steel bed better, its less viscus, but
I did enjoy the weight savings.
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Posted: 10/1/2015 6:42:05 PM EDT

[#2]

Are you lost?

Posted: 10/1/2015 6:59:22 PM EDT

[#3]

Now I used the rest of the Devcon I mixed up to bed the top handguard
and the scope mount. I’ve never bedded a scope mount before but I liked the
results and I think I’ll do it again. I’ve also never bedded a handguard but
with the amount of wood I had to cut out I wanted the strength the Devcon would
add.

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added a block of wood to fill in the rear sight cutout, whittled it down to fit, and stained to match (sort of)

Posted: 10/1/2015 7:17:10 PM EDT

[#4]

Interim fitting was achieved using two crush washers; a .30
cal crush washer to center the tube on a .223 cal crush washer which centered the
whole assembly on the barrel. I used a Damage Industries muzzle brake with a
thread adapter from Dakota Silencer to tighten the whole thing down. This whole
set up is temporary, I will be machining some custom hardware to keep
everything perfectly aligned at a later date, but it was good enough for now. I
threw on my new Trijicon Accupower and went hunting two days later.
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Posted: 10/2/2015 11:48:07 AM EDT

[#5]

Cool.

What did you just do?

Posted: 10/2/2015 12:05:37 PM EDT

[#6]

Quote History

Quoted:
Cool.

What did you just do?

View Quote

Posted: 10/2/2015 1:56:21 PM EDT

[#7]

Quote History

Quoted:
Cool.

What did you just do?

View Quote

Posted: 10/2/2015 4:13:54 PM EDT

[#8]

Hah, still doing it

Basically I'm building a rifle with a tensioned barrel so that it shoots like a heavy weight barrel, but weighs much less than a heavy weight. I'm doing it to this gun as a proof of concept, as I plan to tension an AR barrel next.

You can see a bit better in the picture below, with the top handguard taken off.

Here I turned a few 303SS end-caps for the Carbon Fiber to make sure it holds together under the stress (really I just cut the carbon fiber too short and had to buy 1/8th of an inch).

Posted: 10/3/2015 2:00:57 PM EDT

[#9]

Range report? How much does it weigh? I would love to see more pics of the carbon fiber tube and barrel after you turned it down.

Posted: 10/3/2015 2:39:14 PM EDT

[#10]

How much tension are you putting on the barrel? How much do you lose as it heats up?

I'm too lazy to do the math right now but my gut feeling is that the amount of compression the carbon tube will withstand is not enough to significantly tension the barrel that a 200F rise in temperature wouldn't relieve, coupled with the low conductivity of the air pocket the carbon sleeve creates around the barrel. I think you have something that will perform like you hope (a lightweight bull barrel) for a few rounds and then begin to change significantly both in POI and group size. Which is fine for a hunting rifle, but I don't know that it makes sense on an AR.

But don't let me stop you, I'd like to see how it turns out as I've toyed with the idea in the past, and my opinion has stopped me from actually attempting it.

Posted: 10/3/2015 3:02:14 PM EDT

[#11]

It took me a bit but I finally understand what you mean by tensioning the barrel.

You put a sleeve, carbon fiber here, around the barrel. It sits on the ridge near the chamber and when you tighten the muzzle device, it pulls tension on the barrel, stiffening it. Correct?

Posted: 10/3/2015 9:13:02 PM EDT

[#12]

I understand how it would work on lighter calibers but as you get into the heavier calibers does this method reach it's limitations? Must have been to much exitment for OP.

Posted: 10/3/2015 11:31:52 PM EDT

[#13]

Good luck, carbon fiber barrels are well known to be pretty useless, they perform worse than a plain steel barrel.

Posted: 10/5/2015 12:06:45 PM EDT

[#14]

Oh man, let me answer in order here.

Robert V77

Range report: not enough data, fired about 10 rounds of 130gr. Winchester with spectacular results, good enough to make me pursue this farther, then I shot some Barnes solid coppers with OK results, then I went hunting and got a pig at about 110 yards (after missing one at 90, but that was my fault not the rifles).

Weight: It's still a Mauser, with a WWII era stock (with all the extra steel bits) I will get back to you with a quantifiable weight, but for now lets just say I have lighter rifles. Ill get you more pictures soon.

Kuraki

The tension right now is not set, I plan to work on my load development and refine that, then tension the barrel until my groups size goes down (like a harmonic resonator). Then of course when that's all done ill have to re-machine the muzzle brake so that the tension is correct and the ports go to the sides instead of up and down. From my chart my 20" barrel at 70 degrees will be 20.002" long at 90 degrees.

Captain

Correct, but I'm hoping it also works to reduce vibrations and increase accuracy that way too.

Misc and Gamma

I honestly don't know, but I'm having fun. Please remember I'm not comparing a Proof Research Barrel to a Lija here, I'm trying to make a $90 barrel on a $100 gun shoot like a $700 set up or better by adding about $30 of carbon fiber and my meager machining skills.

Then I'm going to do the same thing to an AR in the interest of making a rifle light enough for my wife to shoot comfortably that doesn't group terribly after 3 shots.

As a placeholder for more technical pictures, here is my lab assistant.

Posted: 10/10/2015 3:32:44 PM EDT

[#15]

It's like 1977 all over again...

...

http://www.google.com/patents/US4211146

ETA ------- Neat lookin doggie...!

Posted: 10/10/2015 4:34:09 PM EDT

[#16]

I remember reading that it is one reason the Dan Wesson revolvers were accurate. The barrel is "stretched" between the frame and the muzzle end of the shroud.

Possible problem with the AR is you'll be pulling on the barrel nut that is threaded on to an aluminum receiver. Not sure how much you could torque it to tension the barrel, or "tune the barrel" through tension.