How to tighten up my group.

[Bart B]

[ QUOTE ]
Different brass might have slightly less or more case capacity affecting your barrel harmonics.

[/ QUOTE ]I disagree with this.

A barrel fitted to a receiver that's screwed into a stock will have one frequency it vibrates at. That doesn't change. Its harmonics will remain the same regardless of what the details of the cartridge are that's fired in it. A barrel's resonant frequency doesn't change with the ammo; it's fixed due to the mechanical properties of the barrel, receiver stock and sights.

It doesn't matter where in the barrel's whip pattern a bullet leaves. As long as its the same place for each shot, accuracy will be good.

 

[kraky]

Bart...you sound like you have more engineering background than me. I can only go by my experience and that reported by excellent reloaders. If the barrel is so rigidly fixed and harmonics don't come into play why do so many people report tightening groups with different primers.....seating depths...slight changes in speed....ie loading up or down?
What is it that you are saying is THE THING that changes?
Not trying to be a smart alec----just trying to understand your viewpoint. I imagine harmonics as being the movement of the barrel during the exciting time from the ignition of the small bomb in the chamber (Ie cartridge) to the passing of the relief valve (bullet) down and out the explosion confinement tube (barrel).

 

[davewilson]

Karky, a barrel doesn't even vibrate once in the time it takes to ignite and exite the barrel. different loading components just make for more consistancy.i'm sure Bart will explain this in much more detail.

 

[Bart B]

[ QUOTE ]
Bart...you sound like you have more engineering background than me. I can only go by my experience and that reported by excellent reloaders. If the barrel is so rigidly fixed and harmonics don't come into play why do so many people report tightening groups with different primers.....seating depths...slight changes in speed....ie loading up or down?

What is it that you are saying is THE THING that changes?


[/ QUOTE ]I don't have a mechanical engineering background. I have worked with and shot matches with some who do and they've shared a lot of simple physics stuff with me. One of them is the resident mechanical engineer for the US Olympic shooting team who has acutally measured how a barrel whips/vibrates when a round's fired in it.

Virtually all rifle barrels have a resonant, fundamental frequency somewhere between 40 and 80 Hz (Hz = Hertz, used to be called CPS or cycles per second). When the barrel's screwed into an action, its resonant frequency will change a little bit. And it'll change a little more when that barreled action's screwed into a stock then sights attached.

When you tap a complete rifle's barrel with something and hear that high frequency ring, that's somewhere in the 2500 to 3500 Hz range. That high-pitched sound is caused by sound waves traveling back and forth through the barreled action at about 18,000 Hz; 17 times faster than through air. This high frequency is a harmonic about 40 to 60 times the stocked barreled action's resonant frequency and is about what the top 10 piano keys make.

Most of a barrel's whip when fired is in the vertical plane. And that whip is at the resonant, low frequency. The high-pitched frequency we hear when the metal's tapped causes vibrations so small in size they are meaningless. But folks hear the ringing and it's normal they would think that this high frequency is the one that's important to timing the bullet's exit at some ideal point in the barrel's whip.

With a barrel's resonant frequency making it whip vertical somewhere between 40 and 60 Hz, that means one complete cycle will happen in 1/40th to 1/60th of a second; 25 down to 16.7 thousandths of a second, or milliseconds. Most centerfire bullets take about 4 to 5 milliseconds to leave the barrel after the firing pin's released, smacked the primer and the powder burns pushing the bullet out. Which means the bullet's gone before the barrel's barely started one whip cycle.

So I think the idea that one can shoot a bullet at the correct speed such that it leaves the barrel when the muzzle's at the top or bottom of it's whip (when the least movement is happening) is a misconception. A given rifle's barrel has only one frequency it whips at and different bullet weights have different lengths of time it takes for them to leave the barrel. I don't know of anybody who has actually measured a barrel's vertical whipping along with determining where in that cycle the bullet leaves the muzzle. But there's a lot of conjecture and opinions around as to what happens and when. As far as I'm concerned, as long as each bullet leaves at the same point in the barrel's whip cycle, best accuracy will happen. And I don't care where that point is.

I don't know all the details of why one set of components shoots more accurate than another set. Nor how changing the way a given set of components are assembled will change the accuracy produced. I don't think anyone knows all the reasons why load A shoots more accurate than load B. All I know is that accuracy is the reduction of all variables to as close to zero as possible. And some combinations of components and assembly techniques seem to work better than others.

 

[keithcandler]

Lefty, some simple basics to re-think..

I shoot some of the Barnes Tripple shock bullets, they are very accurate and foul less than a Nosler bullet for sure. What is an absolute about the Barnex Tripple shock bullets is that they like a certain amount of Bullet jump. When you find that "sweet spot", it's like hitting a home run.

In most of my hunting, the first shot is the most important shot. I can count on one hand the number of times that I have had to shoot more than one shot, and in almost every case, that was at running animals.

Concentrate on making that first shot being the most accurate. The way that I accomplish this is to have the first shot seated longer to touch the lands or what ever bullet jump the gun likes. ON the second, third shots, the bullet is seated the longest that will fit in the magazine.

I dip the brass that I intend to seat the bullet longer, in an instant blueing solution to a point just above the webb of the case, which turns the back end of the case a dark color, easily seen.


Primers make more of a difference than most people would like to think. Some of the 7 Mag rifles will shoot a standard 9 1/2, others like the Fed 215 or CCI-250 and I have one gun that will only shoot the Win Mag primer accurately....you just never know.

On these large magnums, when you are doing your test loading, you must clean your rifle anywhere between 12 rounds to 20 rounds, every gun is different, but I have experienced less copper fouling from the Barnes Tripple shock bullets than anyother bullet that I have ever fired.

When you are shooting, let your barrel cool down. I cool my barrel by dousing the outside with rubbing alcohol on a paper towel, which cools the barrel in a couple of minutes, and you should oil the outside of the barrel when you are through shooting a blued barrel.

Many of the posters have given you some great information, and we wish you luck on your rifle.

 

[Aussie]

lefty ,
Either there's a lot of cart before the horse happening here or others are making very positive assumptions about your level of reloading and load development experience .
How did you arrive at your chosen powder charge ? Did you work up at 0.3 gn or 0.5 gn increments checking and comparing each charge weight for accuracy ? Alternatively did you try a ladder test ?This is basic stuff and comes long before you start stuffing around with different primers , seating depths or neck sizing vs FL sizing .A half grain change in powder charge can halve group size or double it , particularly in a sporter weight barrel . In small cartridge cases you can measure accuracy differences with 0.2 gn changes in charge weight .
What you are looking for is a charge weight that produces a group with minimal vertical dispersion . Most horizontal dispersion is usually due to shooter error , rifle / scope problem or wind .
If you can't find a charge weight that provides
acceptable vertical dispersion then the first place to go is a change of powder or projectile . There's only one way to develop the most accurate load for your rifle and that's systematic trial and error . To minimise wasted time , effort and money you should start with the factors that have greatest influence first .

 

[lefty15]

I got the load data for the bullet/powder combo right from Barnes with the suggested min/max powder charge,and yes I did load up various different powder charges and compared group size, to find the best shooting load. I am currently shooting about a 3/4"-1" group consistantly at 100 yards.
I just want to tighten this group up a bit more if possible.
From what I understand .300 WM'S like a longer overall length, but I am limited in my overall length because of my clip.
You guys here have alot more knowledge about reloading than myself, and all I am trying to find out is if someone knows a little trick to make my group a bit tighter.

 

[Aussie]

lefty ,
Group size may improve further with incremental seating depth changes , even if that means deeper seating . Think that is the logical next step . After that I'd probably go to neck turning and use of a bushing die for neck sizing to get consistent neck tension . Case sorting by weight maybe . Others may have different priorities .

 

[chain]

My 300 win shoots 180 and 200 gr Accubonds in less than MOA with H 1000 or RL 22, it will shoot 180 SGK's the same with IMR 4831. These are partially re sized and .050 from the lands.