My new project, tensined barrel with muzzle brake

[Dolomite_supafly]

Here are some pictures of a newly completed project.

This is a Stevens 200, same as a Savage except it comes without a Accutrigger. It has a Sharp Shooter Competition trigger. It sits in a Stockade PDS/T stock. The gun was put together a long time ago, before my accident, but I decided I no longer wanted the heavy 26" bull on it because it was heavy.

It has bolt lift kit to ease the heavy bolt, longer bolt handle to help out as well. The bolt has been completely been gone through and had everything cleaned up internally. Firing pin protrusion set to .040".

Now the interesting part, the barrel. The barrel started out life as a sporter weight barrel. I had it machined concentric to the bore to a thinner profile. I had the muzzle threaded 1/2-28 as well. I had a shoulder machined at the chamber end. This is for the tensioning (SS) tube to ride on. The stainless tube is over the the pencil thin barrel. The muzzle brake has a shoulder machined on it as well for the tensioning tube to ride on.

To install you machine the tensioning sleeve so it is just long enough that the brake is about a 1/4-1/2 turn away from where you want it to index when the barrel is cold. Next take a torch and heat the barrel, not the tube. Not red hot or hot enough to cause the steel to change but hot enough that you can't touch it. This causes the barrel to lengthen enough that you can tighten the brake down to the point where you can index it where you want it. After the barrel cools it tries to shrink back down again but can't because of the tensioning sleeve. All of his puts a fair amount of tension on the barrel as well as locking the muzzle brake in place. It is this tension that seems to help the thin barrels.

There are a number of advantages of using a tensioned setup. First is it eleminates any heat related drift. I have had a number of guns with thin barrels that had a heat related drift and in every one having it tensioned solved it. Second the pencil or sporter weight barrels seem to be more rigid and as such seem to be more tolerant of various ammo types. It is the barrel whip that causes some barrels to be finicky about the ammo they like. And finally weight, with all the advantages of a heavy barrel this barrel weighs less than half of a comparable heavy bull barrel. In a previous version this same barrel has shot .2's-.3's with handloads it liked.

There is one disadvantage ot this setup. It is heat build up. The tube doesn't allow heat to dissipate as fast and if heat builds up too much the sleeve can loosen. I have never had one shoot loose unless you shoot it enough to get the barrel hotter than when the sleeve was installed which should not happen under normal conditions. You will see the groups go to hell if the sleeve starts to come loose.

Dolomite

Edited March 18, 2011 by Dolomite_supafly

[peejman]

Interesting, I've never heard of doing this. What size is the tube and what's the OD of the barrel?

[graycrait]

Interesting. I knew a couple of tensioned .22 barrels existed, but had not looked at centerfire. I did a little reading and it seems you have your work cut out for you. Doesn't the tension change as the barrel heats up due to material differences reacting to heat differently? It sounds like fun though and puts you at the cutting edge it would seem. Online articles for centerfire tensioning don't go back too far with any volume. I wonder if anyone at this website has done similar work: AccurateShooter.com 6mmBR.com -- Best Guide to Precision Shooting and Precision Rifle Accuracy

[Dolomite_supafly]

The barrel runs approximately .5" at the muzzle and tapers up to .87" at the shoulder for the sleeve to rest on. The shoulder is the same OD as the sleeve at 1". The wall thickness is .065 on the tube that is 304 stainless.

The amount of tension may change some with heat but in all the others I have done I have never noticed a change in groups unless the sleeve works loose and you will see a dramatic change. If I ever run into the rpoblem of it working loose I will just heat the barrel more next time.

I have done this to 223 rem, 308 win, and a 7.62x25 tok that was designed and built to shoot subsonics. I have also done rimfires as well. Most of the previous ones were done before my helicopter accident. Since the accident something that might have taken a day before now takes weeks because I can't do anywhere near as much as before and absolutely any physical activity at all puts me in bed for a few days.

The biggest reason for doing this with a muzzle brake is I wanted a lightweight, light kicking rifle. It weighs 8.6 pounds compared to the 14+ when it wore the bull barrel. It may only be a 223 but with my injuries even recoil from a 223 causes me problems. I do have a very accurate AR that also wears a brake but I wanted something unique.

It will be interesting to see what the velocity will be with teh 18" barrel compared to the 26" that was on there. The tensioned one is a 9 twist and the 26" one was a 7 twist.

Dolomite

[graycrait]

Keep us updated on success and failures, there is always something to be learned, unless you are heading to a process and product that could go commercial, then best to keep secrets secret.

Thanks for posting this. I enjoy "listening" to people who are enthusiast about "stuff" and apply some energy and gray matter to solve a problem or create something.

Craig

[Dolomite_supafly]

There is another guy on another board that came up with the idea right after I posted my initial one. He now produces them but has some flaws because I didn't get into great detail with him.

I have zero intentions of doing this commercially. I can't do it physically and probably not mentally.

I just do my crazy projects to see if it is possible.

Dolomite

[Jasongar8]

I have never heard of this either. Very cool project though. Nice work.

[Dolomite_supafly]

Just shot some groups and they were erratic so I took the tube off. Groups tightened right up. I suspect there wasn't enough tension on the barrel or at least it acted like it. This same barrel was tensioned before when it shot the .2"-.3" groups on several occasions.

Going from a 26" barrel to a 18" barrel cost me ~260 fps and now is 2694 average.

Going to have to rethink the idea for now and probably put the heavy barrel back on for now. At least it will mitigate the recoil even though it is heavy.

Dolomite

[mikegideon]

Have you tried cryo on a skinny barrel? I cant decide if it's worth persuing, but might give it a shot if I had barrel in hand. 35 bucks...

Cryopro Cryogenic Tempering Processing Center

[Dolomite_supafly]

I am skeptical but you never know. It makes sense and I know it helps things other than barrels.

When I get a chance I will spend some more time on it. I am pretty much done now as far as being able to do anything else.

Dolomite

[graycrait]

Food for thought here: Charles E tensioned barrel ?

[Guest GunTroll]

Have you tried cryo on a skinny barrel? I cant decide if it's worth persuing, but might give it a shot if I had barrel in hand. 35 bucks...

Cryopro Cryogenic Tempering Processing Center

From Shilen Barrels,

If you have heard that the cryogenic treatment stress relieves steel, this is false. We have measured the residual stress in 4140 and 416 steel with a process called x-ray diffraction. After much R&D, we have not been able to measure any changes in molecular stress after cryo treatment. For this reason we do not endorse the cryogenic process, but we can safely say that it is not detrimental to the barrel either.

Welcome to Shilen Rifles, Inc.

And as to your project Dolimite,

You are an interesting fellow. Its great that you are trying different ideas or thinking outside of the box. Your projects make me think. Good job. Bummer on your current projects results. You'll get it right.....that I'm sure.

Question, you mentioned that the barrel does heat up and that the heat doesn't dissipate well. Have you thought of any ideas to combat this. Ports/holes perhaps in the outer tube?

[Dolomite_supafly]

From Shilen Barrels,

If you have heard that the cryogenic treatment stress relieves steel, this is false. We have measured the residual stress in 4140 and 416 steel with a process called x-ray diffraction. After much R&D, we have not been able to measure any changes in molecular stress after cryo treatment. For this reason we do not endorse the cryogenic process, but we can safely say that it is not detrimental to the barrel either.

Welcome to Shilen Rifles, Inc.

And as to your project Dolimite,

You are an interesting fellow. Its great that you are trying different ideas or thinking outside of the box. Your projects make me think. Good job. Bummer on your current projects results. You'll get it right.....that I'm sure.

Question, you mentioned that the barrel does heat up and that the heat doesn't dissipate well. Have you thought of any ideas to combat this. Ports/holes perhaps in the outer tube?

I thought about a shroud full of holes like a MG shroud but that would look a bit silly on a bolt gun. The next thought was to seal it then fillit with a liquid of some sort to carry the heat to the sleeve or even setup a jug to cool like the water cooled machine guns. Haven't tried any of the liquid methods yet. Another option might be to machine the barrel with a straight taper then use an aluminum heat sink as a tensioning sleeve. Basically drill the heat sink to the same OD as the barrel, heat it then install it. After that tighten the tensioning nut down as tight as I can get it. The only problem is the galvanic reaction between the aluminum and the carbon steel. I guess I could mitigate that using thermoconductive grease.

The reason why it didn't work this time is I didn't have enough tension on it. This same exact barrel has been tensioned before just not with a muzzle brake as the tensioning nut. In its previous version it shot .2's and .3's with regularity using handloads. The previous version was really torqued down while this time is was just a bit more than snug it turns out.