"Tuned" rifle barrel length

T

TXAZ

New member
I was listening to a discussion regarding finding the sweet spot on the length of a barrel for maximum accuracy. The gist of the comment was that upon pulling the trigger, the barrel starts to vibrate, and there is a specific length for every caliber and load that will provide the best, measurable accuracy.

Any truth to that you guys know about?
 
The only place I know of where a bunch of work was done for finding the best barrel length is found by Googling for "Secrets of the Houston Warehouse". They found that 21.75" was the best for tight groups. SFAIK, that held for all the cartridges they messed with.

I don't guess I've ever worried about "sweet spot". I happen to like longer barrels for the higher velocities available--but that's just me. So what I've always done is to tweak with the forearm bedding and sorta explore various load combinations as to what powder--and how much--with which bullet.

Being more of a hunter than a paper puncher, anything under one MOA has always been sufficient. I've worked up a fair number of combinations which were sub-MOA, but that was as much for the fun of it as for utility.
 
Well as to .22 rimfire it is a fundemental principle behind most custom made bench guns and where allowed virtually all of them utilize tuners on the end of the barrels.i
 
everything you wanted to know about barrel harmonics but was afraid to ask

http://www.rifle-accuracy.com/harmonics.htm

with a centerfire if you handload you can do what is called a ladder test using various powders.

http://www.6mmbr.com/laddertest.html

unless you are into LR match shooting or rimfire BR it is not worth getting a headache over though.

A trick I have seen a friend use is 2 rubber orings on his barrel and some small magnets captured between them. He slides the orings and magnets back and forth on his barrel to tune it. Looks funny but I have seen him do 1.5 -2 inch 5 shot groups at 600 yards with a 223 so there must be something to it.
 
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I don't agree with that theory.

Don't forget that the barrel harmonics are affected by the bullet, as well as the powder type, and the powder charge...

There are a lot of variables that affect the harmonics. I'll try to find a link to the article I'm referring to, but essentially the barrel resonates from breech to muzzle. The trick is to get the bullet to leave the muzzle while the resonance is at the breech end, and the muzzle is stable in space.

This could be accomplished with barrel length for a particular load, or more simply by finding the sweet spot for the bullet/powder/load combination that accomplishes the same thing, for whatever the given barrel length is.
 
Air Gauged Barrels

Cut the barrel at the smallest groove diameter nearest the muzzle. Or get Douglas air gauged barrel. Those that measure .0001" or less variation from one end to the other are classed as air gaged. Shilen- "Our air gauges are accurate to 50 millionths of one inch."
 
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Came across this thread searching for "barrel harmonics" and want to add a few things.

First off, the "harmonics" a barrel vibrates are higher multiples of its fundamental (resonant?) frequency. The fundamental frequency is the one it vibrates at with the most angluar change in bore axis at the muzzle. Virtually all rifle barrels' fundamental frequency is below 100 Hz (cycles per second) So, if a barrel's fundamental frequency is 80 Hz, its first harmonic is at 160 Hz, the second harmonic's at 240 Hz and so on. It's this fundamental frequency that causes the muzzle axis to move up and down vertically. That's because the recoil axis is abobe the center line of the rifle causing the bore axis to move up in recoil while the bullet's going down the barrel.

Second, it doesn't matter what components one uses in a given barrel. It whips at the same frequency for all of them. How much depends on how powerful the round is. It's the barrel's metallurgic properties that determine how rigid it is. Not how hard it's smacked or what it's smacked with doesn't matter. Once the barrel's made, its properties stay the same. And bullets are long gone before a center fire rifle barrel goes through one complete cycle; first up, then all the way down, then back up to where it was when the round fired. If a barrel's fundamental frequency is about 83 Hz, it takes 12 milliseconds to go through one cycle. Typical center fire bullets take 1.3 or so milliseconds to go from case mouth out the barrel.

That high frequency ring (3000 Hz? or thereabouts) is just the sound wave going back in forth in its length. There's very little muzzle whip caused by this high frequency. But many web sites state this is the frequency their barrels whip at that causes bullets to strike high or low.

After a barrel's fit to a receiver, the barreled receiver will have a different fundamental frequency. Bolt a stock to it and it'll change. Mount a scope on it and more change take place.

And nobody's ever timed modern rifles' bullet exit to where the muzzle axis is when it leaves. But the smarter internal ballistics folks feel it leaves while the muzzle's on its first upward swing before the muzzle axis starts back down. It's a myth that best accuracy happens when the bullet leaves at only the top of the muzzle axis swing; they're going too fast.
 
There are a few ways to tune a load/barrel to produce the best accuracy. Using factory ammo, the only ways to tune a barrel/load are: 1. choose various types of ammo, or 2. to physically change the rifle, either by pressure point, shortening the barrel, or by using a tuner.

By handloading, tuning can be accomplished by changing: bullet types, weight, powder type/charge, cases, primers, and seating depth. Of these, seating depth seems to be key element. Finding the right seating depth involves shooting groups of 5 rounds, starting with a seating dept that puts the bullet ogive about .001" off the lands and going about every .002" backward to about .015". If the sweet spot is found between those two distances, ti can be further refined by going to increments of .001" on either side of the preliminary sweet spot. If not, keep going back until a second preliminary sweet spot is found.

My rifles seem to shoot various bullet types well at the same seating depth, but your results may be different.
 
Google "Dan Newberry OCW". You'll find every thing you could hope to learn on Dan's page, including how to work up a load based on his theories.

The basic idea is that the shockwave from ignition makes several trips up and down the barrel before the bullet exits. If the occultation is at the muzzle when the bullet leaves, the group will be erratic. If its at the breech, the group will be small.
 
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www.ozfclass.com/articles/1/psm_2005_03.html

Here's Bill Calfee's article on it. Or one of his articles. He's published a bunch of them in Precision Shooting.


Harold Vaughan touches on it (along with everything else) in his classic book 'Rifle Accuracy Facts'. Of course it helps to be a rocket scientist to read his writing because that's what he was. I struggled with it a lot and I was physics major way back when.

"Following World War II, where he flew 100 combat missions in P-47s and P-51s in the Pacific Theatre, the author joined Sandia National laboratories in New Mexico where he became recognized as the grandfather of the Aeroballistics/Flight Mechanics Technology base for nuclear ordnance…obviously a pretty brainy guy. During the last few decades he became fascinated with rifle accuracy "

John
 
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Several prior posts have mentioned..

using a "tuner".

A few years ago, Browning fitted rifle muzzles with such a device - which they called B.O.S.S. (Ballistic Optimizing Shooting System, IIRC).

When Browning and Winchester were owned by the same company, for a few years, the Win Mod 70 was also available with B.O.S.S.

It came with and without a muzzle brake, I think. You tuned the barrel length by screwing the BOSS in (shorter barrel) or out (longer barrel). I don't know the total range of length available. Browning even went so far as to sponsor target matches which only allowed owners of their factory installed BOSS equipped rifles to compete. I never heard anything about how small the winning groups were. I wonder how they compared to bench rest competitors?

Then they disappeared from the market and haven't been heard from lately.

Simms Vibration System now makes a "rubberized" tuner that slips over the muzzle of the barrel and can be slid up and down until you find the sweet spot, THEY CLAIM.

I'm just saying.:rolleyes:

Has anyone here had any experience with BOSS and/or SVS?:confused:
 
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Regarding the following comment about Dan Newberry's OCW,"
You'll find every thing you could hope to learn on Dan's page, including how to work up a load based on his theories.

The basic idea is that the shockwave from ignition makes several trips up and down the barrel before the bullet exits. If the occultation is at the muzzle when the bullet leaves, the group will be erratic. If its at the breech, the group will be small.
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Shock waves travel through steel a bit over 9000 fps. And they don't stop at the barrel's breech end when traveling backwards in the barrel; they continue on to the back end of the receiver (the receiver's steel, too, isn't it, and hard pressed against the barrel?) And they don't start out going forward; another one goes backwards. Where exactly does this shock wave start from? How critical does the timing (velocity or barrel time spread) have to be for a shock wave to be at the breech to make this happen?

Interesting theory, but nobody I know of has verified its credibility. Nobody's ever published any proof any one of those two shock waves' is at a given place for best accuracy.
 
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Well, yeah, I didn't present a dissertation on the theory. there's a lot to it.

As to the validity, I'll leave the argument to Dan and others. I do know that his load development technique works.
 
Read it...crazy....

Interesting stuff, I saw the part where he had his barrel built to 21.75, but nothing about how he arrived at that...

Got a couple of ideas from it ..but some of it, well, it fades to irrelevancy when you're outdoors shooting 600 yards into a full value 15 mph wind.

Getting OT a bit I suppose, but the free-recoil shooting goes against everything I've ever read about proper shooting technique and shouldering a stock.

I can't understand how the rifle doesn't slam back- is the benchrest caliber he's shooting really that light on recoil? If I tried that with my .308, well, it wouldn't be as pretty as these videos...

http://bulletin.accurateshooter.com/2011/03/free-recoil-benchrest-shooting-demonstrated/

Anyone shoot like that off a bench?
 
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Has anyone here had any experience with BOSS and/or SVS
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Yes. I have an Abolt with the system, and my dad uses one of the simms tuner "rubber donuts" on his 7mm08.
The BOSS range of adjustment is around 1". The weight of the tuner/muzzle device is far less than the tuners I've seen for .22rf benchrest.
It does affect group size. The caveat, and I think what sunk the idea for Joe Hunter, is that while you can "tune in" a load, you can also "tune out" a decent load. I've made some great groups with the BOSS, but I have also managed to turn near MOA loads into 3-4 MOA loads as well.
I have to reload for it in an unusual manner. I basically just load up for pressure, find a safe but speedy load with high case fill, and then tune the rifle to the load. It takes an abhorrent amount of ammunition to do this, as small BOSS adjustments can make a fairly big difference in POI and group size. It is repeatable though.

The rubber donut SVS device mostly seems to change POI. While it does alter POI and groups to some extent, the big problem is its lack of repeatability, as it can move fairly easily on the barrel. It's an interesting toy on a skinny pencil barrel, but I'll take a reliable thick barrel and good solidly bedded stock any day over the rubber donut.
 
Does anyone really think building a BR rifle that can weight no more than 10 1/2 lbs including scope/rings in calibers that most have never heard or shot should set the standard for barrel length @ 21 3/4"?
 
old roper asks:
Does anyone really think building a BR rifle that can weight no more than 10 1/2 lbs including scope/rings in calibers that most have never heard or shot should set the standard for barrel length @ 21 3/4"?
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I don't.

Back in the early 1970's, someone else was testing his .308 Win. match rifle with a Hart 26-inch barrel stuck in a pre-'64 Win. 70 action conventionally epoxy bedded in a wood stock. The rifle was clamped in a machine rest so it could be shot in free recoil. It shot several 10 shot groups at 600 yards ranging from 1.5 down to 0.7 inches with some 185-gr. bullets. Then shot a 40-shot group at 600 that was 1.92 inches. Does this mean that a 26-inch barrel is best for the .308 Win.? I don't think so.

I put 20 shots into 3.25 inches at 800 yards testing a .308 with a 30 inch barrel.

And the .30 BR round shooting 135-gr. bullets from 21 to 24 inch barrels with 1:17 or 1:18 twists shoot in the low ones winning benchrest matches.

As long as the barrel behaves the same for each shot fired, I don't think it makes any difference how long it is. As long as the powder charge burns uniformly enough to have a very low muzzle velocity spread. And I don't think it's caliber specific, either. Accuracy is everything being repeatable; doesn't matter what size the hole in the barrel is.
 
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