walking group

[old roper]

Well, here is clip from a BR gunsmith and go to bottom and read how he build his rifles and they are glued in actions.

http://www.bordenrifles.com/benchrest.html the Hunter Br rifle is not glue in.

[Bart B.]

Old Roper, I think the benchresters started glueing in round receivers to stocks (after making a perfect mating surface by conventional epoxy bedding with a release agent) as soon as they learned heavier bullets torqued (while bullets wend down the barrel) the round receivers loose from conventional epoxy bedding. The 3 position match rifle folks started using sleeves on their Remington receivers in the 1960's for the same reason. That's when I first heard of benchresters doing it. And the barrels didn't touch anything except the receiver face; at least 1/16 to 1/8 inch clearance around it.

Gluing in flat side/bottom receivers isn't needed, but some do it anyway.

[old roper]

Bart B. I only shot BR and all my actions were glued in on my light/heavy rifles.

As to what happened in the 60's not sure what your talking about unless you can name names and where matches were held as their are still some of the older BR shooter/gunsmith around.

In 1971 Ralph Stolle was making limited number of his Panda flat-bottom aluminum receiver. From my understanding 60's few custom action from Weber,Sherman,Hart and Shilen(made in New York) http://www.riflemagazine.com/magazin...117partial.pdf

I had few action that had been sleeved but not for what your talking about as mine never had recoil lug same with lot of BR actions that I used.

[coyota1]

Old roper, did you say that the barrel as well as the action is glued in on some br rifles?

[Sweet Shooter]

Fascinating! One thing I have noticed is that when we bed with upward pressure most stock materials eventually take a "set" relieving the intended pressure over time. My SPS plastic stock did this noticeably. Groups opened up one weekend. I noticed the looseness right away. What to do? Well I tried a little experiment with Paracord. I left the leather pressure pad in the end of the stock under the barrel and wrapped—"whipped" the paracord as tight as I could to hold the stock to the fore-end of the stock. I'm pretty good with knots and my whipping is pretty tight and smart, I melted the ends leaving little tags so that the whipping doesn't undo it's self. Abracadabra all was well again and the SPS turned in one inch groups again.

There is a science behind the cycling of a barrel just as there is when we tune/spine our arrows to our bow draw-weight and draw-length. It's all about finding nodes and anti-nodes as we do when we increase/decrease arrowhead weight to stiffen/soften a shaft. Increasing/decreasing bullet weight can achieve similar results in a rifle barrel, though it's not visible like when we watch an arrow fishtail away from us when the shaft is too short/stiff.

Try the paracod trick. It's not beautiful on a wooden stock but actually adds a little grip to a plastic stock and doesn't look bad. Mine runs for about 2.5 inches in length, along in front of the sling swivel stud. I also added a little superglue to the cord/knot to stop it pulling loose.

-SS-

[Bart B.]

old roper, one of the 'smiths catering to match rifle folks also worked with another 'smith catering to the BR discipline. I shot matches with him and he was the one in the late '60's or early '70's that mentioned some BR 'smiths were gluing in Rem 700 receivers in BR rifles for the .222 and 22 PPC rounds.

Sweet Shooter, yes there is a science behind the cycling of a barrel. They behave exactly like a guitar string. For a give size, length and fit, they both vibrate/whip at the same frequency regardless of how hard they're stressed from external forces; cartridge firing or finger plucking. The only difference between light forces and heavy ones is the amplitude they wiggle at but the frequency stays the same. Shooting different weight bullets across a wide velocity range doesn't change the barrel's node or antinode points. Different bullet speeds will exit at different points in the barrel's whip cycle, but that cycle is constant in frequency but changes in size. People figured this out over a hundred years ago.

[coyota1]

Bart, you said it best. That's similar to a ringing bell.

[603Country]

I think that BartB, in post #5, had the best suggestion. First free float the barrel and see how that works. If it doesn't help, I'd suggest a different stock all together - a synthetic one with the bedding channel or pillar bedding already in place (Hogue makes one, and others do also). If neither of those fixes the problem, I'd go with a new barrel.

I had a friend with a 'walking group' bolt gun in 243 some years ago, and his problem sounds just like the OP's problem. Nothing seemed to fix it, so he finally sold the rifle. The first shot from a cold barrel was Ok, but starting with the second shot and any following shot, the impact point went up and to the right. Had to be the barrel, and that honestly sounds like the OP's problem. Sometimes you just get a bad barrel, though I don't think that it's a common problem.

[Old Grump]

300 wby mag
Swarovski 3-18
180 grain barnes ttsx
78 grains RL19
Clean rifle
2 fouling shots
First two 3 shot groups approx 2" at 200 yds
Then pattern went to 4-6 inches and shots started to walk up and right-left progresivly getting worse...
Fell on my ass pretty hard the other day but?.....
Ideas please

It is a 300 Wby magnum and there is part or most of your answer. You don't say what kind of stock or barrel you have or how many rounds you have through that barrel but I am guessing sporter 26" barrel and fully bedded stock. My gun does the same but my initial cold barrel group of 3 shots, (I don't shoot fouling shots because this is a hunting rifle and I go in the field clean and shoot cold), is a tad under 1 1/2" when I do my part. The next 3 shots if taken soon after are just under 2" and after that the group opens up and you could fry a dozen eggs on my barrel. I am using plain old Remington 180 gr Core Lokt ammo nothing special about it. Left dirty or clean it makes little difference, when the gun cools down I am back to 1 1/2" initial groups. The last few years I learned to limit myself to 5 or 6 shots per session and then go to a different gun. This isn't a gun I am going to use for competition. If I wanted to do that I would put on a heavy match barrel.

Just dos centavos from a dinosaur but I think you are expecting a bit much from a hunting rifle that shoots giddy up go bullets. I use 4350 powder in my reloads, not quite as fast but I gain a little in accuracy, something you might want to think about.

[Sweet Shooter]

@Bart B... Not disagreeing but to clarify... Given that nodes antinodes remain the same for one mass vs another, ei: frequency, Amplitude is to the largest extent the only variable and is affected by the force exerted upon it from the inside or the outside of the barrel. However frequency is a product of how much stress is resident or "built in" (like stretching a guitar string)... so bedding, up-pressure contributes to installing that. Therefore One influences the other. I'm a guitar player (of some 40 years) and it is possible to pluck/strike a string with a given tension (built in) and extract different frequencies depending on how hard you hit it. It is possible essentially to stiffen a barrel by shooting lighter bullets through it.

-SS-

[coyota1]

Sweetshooter, It makes sense (stiffening up a barrel by shooting lighter loads). But.... Bench shooters usually run full throttle with loads. Seems like every answer brings about another question.

[Bart B.]

Sweet Shooter:

Given that nodes antinodes remain the same for one mass vs another, ei: frequency, Amplitude is to the largest extent the only variable and is affected by the force exerted upon it from the inside or the outside of the barrel. However frequency is a product of how much stress is resident or "built in" (like stretching a guitar string)... so bedding, up-pressure contributes to installing that. Therefore One influences the other.

Ok, your may have a point. Please explain why all the mechanical engineering formulas for calculating barrel (or any other long shape such as a bar, solid rod or even an I or H beam) stiffness and resonant frequency do not include some outside force level or axis to make the barrel vibrate at different frequencies. If what you say is true, then all those formulas are bad.

[MLeake]

Bart B., have you seen Browning's BOSS system? It was designed to achieve that effect - tune barrel vibration so a given load leaves the muzzle at a neutral point in the barrel's sine wave oscillation.

[Sweet Shooter]

@Bart B... I wouldn't say "bad" but they rely on "all things being equal" "ideal situation" a perfect world.

Inherent resonant frequency let's say A440Hz for example, is a given per an objects' mass x tension or pressure. I can get A440Hz out of objects of a different mass (barrel length/string length) by building in a different amount of pressure... the greater the mass the more pressure required to make it cycle at the same resonant freq as an object with less mass (some of that pressure is already built in remember). The duration of the affect has a direct effect and thus bearing on that objects' mass (temporary mass) and therefore resonant freq. As you are aware there is an ever changing set of variables and all we can do is try to bring those variables closer together: Bullet size/weight, powder charge/burn rate, neck tension.

In engineering terms I suppose adding buttresses for support also adds more variables.

-SS-

[603Country]

enough with the competing theories of why the gun won't shoot. Regardless of which of you ever wins this discussion, the gun still won't shoot till action is taken. The OP should have the stock bedded or replaced. If that doesn't fix the problem replace the barrel or the rifle. Or...just take it to a top level gunsmith and tell him to make it shoot. I've done that with two rifles and the results were fantastic.

He could be flinching (I probably would, with that rifle), but that wouldn't give repetitive vertical grouping.

And the BOSS is just plain ugly, even if it works great.

[coyota1]

enough with the competing theories of why the gun won't shoot.

This isn't a competition. I believe sharing theories and information is the core of this thread. I have learned something from sweetshooter, and bart, and didn't even bother to thank them. I hope maybe they learned something from me. It's taken a long time for shooters, and barrel makers as to what makes a gun accurate, and there are still unanswered questions. I want to soak up as much info as I can.

[603Country]

This thread isn't a competition but Bart and Sweet (both very knowledgable guys) are sure competing or trying to one-up with theories of barrel vibration. Sure the barrels vibrate. We all know that. The OP knows that, but the info put forth on vibration is not going to help him at all. That's why I suggested that if we want to actually help the guy, who did request our assistance, we need to suggest something a bit more practical than detailed theories of barrel whip. Of course, that practical info is already in the various posts, and the OP may have already taken action to fix his problem. I hope that he'll eventually tell us what did fix the problem. I'd like to know.

And I most certainly agree that I've learned a ton of things on this forum. It's made me a better reloader and a better shot, and I don't think I've ever thanked anyone for the bits of info that have been extremely helpful.

[Bart B.]

Sweet Shooter, if you mean you're laying a finger on that guitar string then plucking it, yes that will change its resonant frequency. Without that finger on it, I think it makes the same note every time it's plucked.

Your reference to A on a keyboard at 440 Hz got me to thinking about a standard sporter weight 30 caliber 3.4 pound 24 inch barrel's resonant frequency. With both ends free its resonate frequency is at about 264 Hz.

Screw the breech end into a receiver bolted in a stock and its resonant frequency goes down to about 68 Hz. This is the one that causes the greatest angular swing of the muzzle axis.

If you smack that barrel with a hammer, it'll ring at a frequency much higher than these; couple thousand Hz for example.

[MLeake]

Bart B, that assumes that the tension on the string remains constant, a combined function of both the key, and the temperature - temperature will affect both the length of the string, and the shape of the neck.

Which actually is a good parallel for the rifle.

603Country, sometimes a discussion of theory helps people understand why the different, practical methods work, or which of the practical methods is more likely to apply.

Whether the OP needs to do anything is another matter. He has a hunting gun, not a target gun, and apparently his groups are fine until he has fired several magnum rounds. He just needs to allow cooling off time between his groups, when sighting in the rifle, and may not need the expense or effort required to free float it or fully bed it.

If he were planning on being able to use it for extended shooting scenarios, that would be different.

[Sweet Shooter]

@Bart B. Sweet Shooter, if you mean you're laying a finger on that guitar string then plucking it, yes that will change its resonant frequency. Without that finger on it, I think it makes the same note every time it's plucked.

Bart, this is not the case. Almost and maybe in a perfect world and to all extents and purposes yes absolutely, but not quite in this case.

@coyota1... Thank you.

@BB1... If you're still around... pressure pad+paracord

@603Country... Take a nap. I didn't mean to offend anyone. Sorry.

-SS-

[Bart B.]

For those who think a rifle barrel's resonant frequency significantly changes enough to be noticed with different forces applied to it as well as its temperature in a range where humans survive, please contact Tom Irvine at:

[email protected]

...about his website:

http://www.vibrationdata.com/StructuralFE.htm

...then tell him to fix his software in the above web site that's named below:

"Natural frequency of a rifle barrel with free-free boundary conditions."

so it will match your theories of how such things will happen.

Then be ready to explain why his software is wrong.

Also, contact the American Society of Mechanical Engineers and have them suscribe to your theories because if Tom Irvine's wrong, there's got to be hundreds (thousands?) of engineers working with vibration issues that are also wrong.

[603Country]

Sweetshooter, I took my nap, had breakfast, and the competition/disagreement/argument is still on. That's Ok.

[MLeake]

Bart B, the rifle responds to temperatures in a range created by firing of its cartridges. Humans don't survive in rifle barrel temperature ranges, especially not temperatures such as those created by seven or more shots (OP said problems start sfter first two groups) of .300 Wby Mag.

[Bart B.]

MLeake, I know that. I explained why in post 5 for this thread:

Barrels walking point of impact as they heat up is typically caused by the barrel is fit to the receiver with uneven pressure around where its flat part is against the receiver. If the receiver face is not square with the chamber axis, there'll be one point where the barrel is hardest against the receiver. As the barrel heats up and expands, a stress line at that point makes the barrel whip more and more in one direction as it gets hotter. Which is why, after letting the barrel cool down, it shoots back to point of aim where it started. This cause is easy to fix; face off the receiver and shim the barrel so it clocks into the same place keeping headspace correct.

If a barrel's not properly stress relieved, they also will bend a bit as they heat up. Replacing it is the only solution.

His barrel's fundamental/resonant frequency doesn't have anything to do with that.

Yes, I've heard of and seen the BOSS system on Browning rifles. Adjusting it changes the length of the barrel mass which changes the barrel's resonant frequency a small amount. It does not tune barrel vibration so a given load leaves the muzzle at a neutral point in the barrel's sine wave oscillation. There's no way anyone could verify that without accelerometers on the barrel feeding computer software along with bullet exit times to verify it did. If by "neutral point" you mean when the muzzle axis is straight out from the chamber, that's the worst place to have bullets exit. That's where the muzzle axis goes through the greatest amount of angular vertical swing in a given amount of time. There's no way one could get muzzle velocity spread low enough to do that consistantly. Also, if the muzzle axis is on the down swing as it goes through that point, faster bullets will leave at a higher angle and slower ones at a lower one; exactly the opposite of what's best. So one would have to ensure the muzzle axis is on the up swing when that happens. And muzzle velocity spread would need to be much smaller than what's acceptable for the best place in the vertical plane to leave at.

Browning claims their BOSS adjusts the barrel whip so bullets leave at the top or bottom point in the muzzle axis' vertical swing. I don't know if they proved that with equipment to acutally measure bore axis angle vs. bullet exit or just assumed this to be so like virtually everyone else making such claims.

It's best to have the bullet exit just before the muzzle axis reaches its highest point so some compensation for velocities faster and slower than the average would leave such that their trajectories would be corrected for. A very small spread in velocity is not needed. And this is what the BOSS system does if it's set correctly. This was proved over a hundred years ago with the British .303 ammo in their service rifles.

One can do the same thing much cheaper with the same results than a BOSS system does by just changing their powder charge weight a bit to change the bullet's barrel time from case mouth to out the muzzle.

With the right set of components in a given load, all the bullets fired from several barrels with different resonant frequencies will shoot sub 1/2 MOA at 600 yards with ease. That was proved years ago in long range competitive shooting. But for short range with .22 rimfire ammo, such "tuners" are popular and they do work well if one cannot find a lot of ammo that has the right barrel time for their barrel's vibrating characteristics.

[30Cal]

I'd let it cool off and see if the behavior is repeatable. If it's just behaving badly all the time, then we're talking about something different than a hunting rifle that shoots badly when it get's hot.