Tensioned Barrels

Know what a tensioned barrel means to me? Had a Sako once that I couldn't make shoot well until I put a piece of a popcicle stick under the barrel and tightened the receiver screws down on it. Then it shot ok.

Get a barrel frozen to align the metal's grain structure.

RainDodger
I own an old early 1960s Sako 222R mag, a Tikka 22-250 and a .308 M595 Master Sporter. With quality ammo or reloads, they all are well less than a MOA.
The 22-250 is guaranteed less than a MOA with specified ammo. It shoots less than a MOA using S&B 55gr. The Master Sporter is a poor man's TRG. Absolutely wicked with Federal BR.
As accuracy is what you pay for; if I was you, I would have returned it.

I've had a tensioned barrel in my M17 bullpup for over a decade and it shoots dang accurately for a gun that wasn't meant for long distance. Having the thinner barrel pulled into tension by the stiffer, aluminum outer receiver was a pretty neat idea by the designers. (That said, there are disadvantages to having a shiny black metal receiver as your cheekrest, but that's easily solved.)
http://www.kmarms.com/ has a modern interpretation of the M17 but they did away with the barrel tube and angled front plate that allowed the barrel to be tensioned. It could always be added if there are any parts left on any of the numerable parts places.

“Tensioned” rifle barrels are what made M1 and M14 match grade service rifles shoot so accurate. The best of them shooting good lots of commercial match ammo or good handloads (not reloads) would put 20 shots inside 4 inches at 600 yards; fired once every 15 to 20 seconds. They had 25 to 30 pounds of down pull at the stock fore end on the barrel. You could squeeze the barrel and fore end together and see the gap between the lower band and stock ferrule open up. Bolt action rifles don’t need that. That tensioning helps mitigate the front end of the op rods bouncing around too much inside the gas cylinder as there is a couple thousandths clearance between the rod’s gas piston and the cylinder; just like car engines but with out expanding piston rings to seal the combustion chamber. You don’t want that piston bouncing around too much causing extra vibrations in the barrel as the bullets go through it.

Why not have your rifle built like match grade bolt guns without any tension on the barrel (they’re totally free floating touching nothing but the receiver) and will put 40 to 50 shots fired several times a minute into 2 inches at 600 yards (yes, that’s been done)? They (along with service rifles) shoot rapid fire matches at 200 and 300 yards with two 10-shot strings each fired in a 1 minute time limit’ they’ll put all ten somewhere inside 2 inches at 300 yards in proper tests. In one special rapid fire match, M1, M14 and M16 rifles are also shot 24 times in 50 seconds at 600 and 500 yards. While nobody shoots them as accurate as a much slower rate of fire would permit, 25 shots inside 8 to 10 inches is not unheard of.

Those rifle’s barrels are fit to receivers whose face has been squared up with the barrel tenon thread axis. The barrel shoulder fits hard and even all the way around it. Not just at one point where commercial rifles do so a stress line’s made in that direction in the barrel as the metal heats up and expands. Have your receiver face squared up then put a shim between it and the barrel when put back together so the barrel clocks in to correct headspace.

Shimming the barrel with something between it and the stock fore end guarantees any change in rifle hold or position will transfer through the bending fore end to th barrel. But it does help a poorly bedded receiver shoot a little better. Nobody builds a super accurate bolt action rifle that way. The down pull on M1 and M14 rifle barrels do require than once the fore hand is slung up with a sling and in position to shoot, do not change the elbow's position else bullet impact will change. It's a lot more change than what bolt guns do because of the tight fit of barrel to stock at that point.

On barrel "tuning" . . . .

Nobody tunes a rifle barrel such that the 'sweet spot' duration where the bullet will exit in line with point of aim for best accuracy. If they did, the bullet would strike below the point of aim down range; gravity at work. When the bore's parallel to the line of sight, that's when it moving the fastest. And if that were possible, all the bullets exiting on the down swing will have the faster ones go above and slower ones below the point of aim; negative compensation. You want the bullets to exit on the barrel’s up swing so the opposite takes place; positive compensation. And the bullet must exit at a greater angle than the line of sight to compensate for bullet drop down range. To learn about this, check out:

22LR Rifle & Tuner
Esten's Rifle & Tuner
Light Rifle & Tuner
Barrel Harmonic Movie
Barrel Tuner Analysis
6PPC Barrel Dynamics

in this web site: http://www.varmintal.com/

You may observe the best place for bullet exit is usually on the up swing just before reaching the high point. Anywhere on the up swing is better than anywhere on the down swing.

There has been something called the "accustrut" for mini 14's available for a while, might be worth looking at. It doesn't tension the barrel but it does limit harmonics and help prevent heat stringing

http://accu-strut.com/

TikkaShooter.... a bit difficult to return a heavy barrel L579 Sako manufactured in '73, which I bought from a private party... unfired and in the box. I did get it shooting pretty well though. It's a .243. Even without the shims.

WA2000 background, not just on tensioned barrel.

http://www.snipercentral.com/walther-wa2000/

Barnbwt;

Once upon a time, a long long time ago, I built my daughter a 10/22. That gun was equipped with a Volquartsen tensionlite barrel. The gun was, and for all I know continues to be, outstandingly accurate. This was before that company began building their own guns. I don't think they offer that exact barrel anymore, but you might consider asking them about their experience with the concept & why they dropped it.

900F

How about a variation of the muzzle device called the B.O.S.S. which Winchester had on some of their rifles in years past? I've seen them on F Open rifles, and their owners shot very well indeed?

The BOSS was for "simple" tuning of resonance for a specific loading.

barnbwt said:

...so the benefits of cryo-treat would probably get lost in the noise of a non-premium barrel blank (to my eyes it looks quite nice for a button-rifled blank to be honest, but it simply isn't a cut-rifled & polished 800$ Bartlein or whathaveyou)

TCB

Click to expand...

I have to question this $800 figure. The last Bartlein barrel I bought was $325 last year. I purchased two Kreiger barrels last month at $340 ea. All Kreigers are cryogenically treated. (for the same low price ).

Yes I understand this is double the cost of a Green Mountain blank. But it seems to me that the goal is to get what extra accuracy is possible for the least amount of weight and cost. My opinion is that the cost of the tensioning system will be higher than the upcharge for a premium barrel and it remains to be seen if it would out-perform the premium barrel. Also, cut rifling barrels have very low internal stresses and tend to move very little with heat.

If the goal is to do a tensioned barrel simply because it needs to be done , I understand.

I'd like to know what the real accuracy of those externally tensioned barrels is. Largest groups shot with a given barrel and the most accurate make and type of ammo.

I ignore smallest groups for anything. There's no way to determine if they happen when everything is perfect, or all the variables in rifle, ammo and what holds the rifle pretty much cancel each other out in all directions. The largest groups shot show what all the variables can add up to. If you shoot enough few-shot groups with anything, one will be sub 1/6 MOA. The guy who holds the 100-yard 5-shot benchrest record of .0077" holds no other records and all his previous groups were a little to very much larger.

The best conventional barrels in 22 rimfire rifles will keep 50 shots tested at 50 yards inside 1/4 inch with good match ammo; 3/4 inch at 100 yards. Sometimes with a tuner weight, other times without. Any externally tensioned rimfire barrel ever done that?

I, and barrel makers I've talked with, don't think a barrel heats up enough to change its resonant frequency and harmonics thereof enough to matter as they heat up and expand. Stainless steels expand about .000006" per inch for every degree F they heat up. If they're completely free floating, they will whip and wiggle at the same resonant and harmonic frequency from ambient to very hot temperatures as normally fired; slow or rapid fire. If they touch anything as they expand, the harmonic frequency of the last few inches of the barrel will change as will it's whip axis. Bullets now take off in some other direction than desired.

make the tensioning struts of a material that expands faster than steel (like aluminum) and size them to maintain a fairly constant force on the muzzle across a certain temperature range

Click to expand...

If the tensioning struts expand FASTER than the barrel, the tension will DECREASE faster.

How about HEATING the barrel and then tightening the tension nut? That way, as the barrel cools, the tension increases, giving you more tension than you could achieve by merely tightening the tension nut.

There are some pretty stout springs on the market, that if you had maybe 5-6 of them surrounding the barrel under the tensioning shroud you could easily put several hundred pounds of pull (if they'd be on the beginning of the barrel I guess the more proper term would be 'push') on the barrel with more than enough wiggle room that the barrel stretching out a few thousandths would't change the tension much if at all. I think.

Would look a bit weird but a 'ring-O-springs' around the base of the barrel might be doable. At least the components for a test rig might not be prohibitively expensive enough to let you try the idea to see if it's viable. If so...then the MKII version could be tarted up to look nice. I believe the idea of the tensioned barrel is sound...and using that to stiffen and support the barrel proper would free you of some of the wall thickness needed seeing as much of it is to prevent whip and distortion as the bullet travels down it like a snake that ate an egg. Externally holding it might very well allow a nice trim barrel that would be lighter and cool faster. Will be a cool experiment anyhow if you try it!

Perhaps tension the barrel, apply the clamp and then release the tension.
(As a "shop" build procedure).

A version of that is how they make pre-tensioned precast concrete structural supports
with interior reinforcing.
(Concrete is strong in compression, poor in tension.)

I, and barrel makers I've talked with, don't think a barrel heats up enough to change its resonant frequency and harmonics thereof enough to matter as they heat up and expand. Stainless steels expand about .000006" per inch for every degree F they heat up.

Click to expand...

Ever shot an early skinny barrel Ruger Mini14 or Ranch Rifle? Mine would walk up the page with each shot. Up and to the right.

Ruger barrels, as well as others not fit to the receiver, all change the amount of whip in one direction as they heat up. The frequencies they whip at don't change.

Ruger's have had a receiver alignment issue with barrels. Adjustment zeroed scopes mounted in rings on them often end up running out of adjustment to get shooting zeros. The barrel tenon threads are not square with the receiver face and torqued in barrels bear very hard at one point around their shoulders. This condition in any rifle causes shot walking as the barrels heat up.

Bart B. said:

Ruger barrels, as well as others not fit to the receiver, all change the amount of whip in one direction as they heat up. The frequencies they whip at don't change.

Ruger's have had a receiver alignment issue with barrels. Adjustment zeroed scopes mounted in rings on them often end up running out of adjustment to get shooting zeros. The barrel tenon threads are not square with the receiver face and torqued in barrels bear very hard at one point around their shoulders. This condition in any rifle causes shot walking as the barrels heat up.

Click to expand...

I wanted to say thanks for all of your informative posts. Whenever I see your username I know that expert level information is forthcoming.

I agree with what you say about looking at the larger groups. Two years ago I had a three shot sub-MOA group at 100 yards, from the standing position. I can never achieve anything close to that consistently, but if you shoot enough groups some of them will be very small.

Corn-Picker, I've put three consecutive shots inside 1/10th MOA at all ranges up through 1000 yards. Once in a great while. With both scope and metallic sights on the rifle. With .308's (bolt guns and Garands), a .264 Win Mag and a couple of 30 caliber magnums.

I don't claim they're sub tenth MOA shooting rifles. But everyone's rifles and ammo are that way. If they shoot enough 3-shot groups, they'll finally get one. Some sooner than others.