What makes the actual cartridge accurate

[BoydAllen]

German,
I will be interested in your comparison of barrels of different twists, but it has been my experience that with my 6PPC barrels are individuals, and to get to their peak accuracies, need to be tuned as such. I have barrels with different rifling forms, manufacturing methods and twist rates. I have learned the hard way to ask a barrel what it likes, rather than to assume or try to tell it. This has allowed me to find performance that would not otherwise been available. Getting back to examples of different twists being better at different ranges, years ago Ruger went to a faster twist in their 7 mags because they found that it gave superior accuracy at long range with heavy bullets.
Boyd

 

[TonyR]

German.
I wonder how changing the seating depth with the SAUM might change the comparison with the 300 H&H or 308 Norma magnum. If Laurie can run the 300 H&H through his action, he should be able to seat the 300 SAUM bullets out in the neck. The standard seating depth for the short magnums assumes feeding through the magazine in a short action. For example, the standard COAL for the 284 Win is 2.800 inches while everyone I know that shoots a 284 Win or Shehane in a macth rifle is seating the heavy bullets bullet out in the neck at a COAL of around 3.2 inches. The COAL for the 200gr SMK in the 300 H&H is 3.655 inches in the Sierra manual while the COAL for the 300 SAUM with the same bullet is 2.820 inches. Should be plenty of room to seat it out in the neck and still work through the action.

 

[GermanS1]

Boyd, I certainly agree that each barrel may need a slightly different load; however, given the real-life constraints of testing three barrels at three distances, I'm going to have to settle for a "good" if not "ideal" load. There's also the complicating factor that all three barrels are in different stocks and have a different number of rounds fired through them. At least they were all chambred with the same reamer. The test will be far from perfect, but maybe something interesting will pop up and then we can follow that lead.

Tony, yes, longer seating depth could definitely help the RSAUM to make up some of that gap to the H&H, an excellent point.

 

[Rust]

IMO, there is a lot more that contributes to accuracy than simply the shape of the case or the quality of the bullets.

Barrel quality is significantly better than it was a scant twenty years ago, let alone 40 years ago. I used to hope for a good barrel since I could not and still can't afford to buy ten at a time and sort through for a good one. Now days a bad or mediocre barrel is much more the exception. Number of lands and grooves, dimensions of the lands and grooves, twist rate, bore taper, profiles, quality of lapped finish, in almost every respect barrels today are superior to anything available twenty years back.

Chamber design. I now longer have barrels chambered with an off the shelf design, they are all ordered to my spec in terms of freebore, neck diameter, freebore diameter, leade angle etc. And it means that the next barrel will be chambered just like the first barrel.

Scopes, and iron sights. Better.

Brass. BETTER.

Powders. While batch to batch variations is still an issue with some powders, finding a powder that closely matches the desired characteristics is much easier given the much greater selection.

Bullets. A lot more to chose from to find the optimal match to the rest of the system.

It is overly simplistic to state that accuracy is soley due to a bullet or case design. Otherwise two of my 1,000 yard rifles would be able to print in the teens with VLDs at 100. Not real consistant about it, usually in the .2s or occasionally the .3s.

And that statement about .270s? I've got a very old 70 with the original factory barrel and stock, with minor bedding that shoots 1/2 moa with a well developed hunting load, with a plain old 3.5-10 hnting scope. Given that performance I don't see why an optimized .270 system wouldn't give a lot of other stuff a run for the money.

But I do think that it's a bit easier using the more common accuracy chamberings since the chamberings have a lot of well developed information available for them. Just pick and chose from the menu for what suits the particular discipline. Which is simpler than optimizing a rifle system for a cartridge such as the .270 which has very little developement for accuracy shooting.

I'd even go so far as to say that a well developed system would only be marginally less accurate that a comparable system with one of the common accuracy chamberings. As long as apples are compared to apples, those chambering appropriate for the intended use. Obviously comparing a 6mm PPC to a .338 Lapua for short range bench rest is not an apples to apples comparison.

Is the 6mm PPC the best for short range bench rest? Currently it is but it only achieves that in a rifle system of appropriate quality.

Those old tests comparing the accuracy of a 30-06 to a .308? Well, as it turns out, in some of them the .308 had an advantage with a leade angle more suited to the bullets used. And if both where using the same bullet, it was one more suited to optimal perfromance in a .308. Is the .308 more accurate? IMO only in some cases where the optimization runs in it's favor.

Which is why I like seeing German plugging along with the venerable -06.

 

[wapiti25]

I found reference to the Rem 40X rifle cartridge accuracy info. What I found was that Warren Page did an article printed in 1968 "Gun Digest" titled "The bigger the package". I found reference to it in a NRA 1981 publication "Highpower Match Rifle Shooting" volume II. It is included in an article by Creighton Audette titled "Handloading For The Match Rifle". The chart is shown on page 73.

 

[BoydAllen]

Another issue ,that requires resources not commonly available, is the SAAMI registered throat design for a particular cartridge. Some have a parallel freebore that is a close fit to the diameter of the bullet, before the leade angle, example .222, others have no parallel section, but rather have a funnel shaped throat that starts at the case neck, that one never sees on at target chamber. Also, lack of correspondence between SAAMI ammunition, and chamber dimensions can be an issue. Have you ever measured how much a FL die reduces the shoulder diameter of a case fired in a factory chamber?

 

[Laurie]

Boyd,

Another issue ,that requires resources not commonly available, is the SAAMI registered throat design for a particular cartridge. Some have a parallel freebore that is a close fit to the diameter of the bullet, before the leade angle, example .222, others have no parallel section, but rather have a funnel shaped throat that starts at the case neck, that one never sees on at target chamber.

dead on!

As an extreme example of this phenomenom I never owned a 7.92X57mm Mauser that grouped well in my days of shooting historic military rifles, or at any rate one that delivered the performance of a good .303" Enfield, 6.5mm, or 7mm Mauser. Putting lots of handloading effort into them would run up against a brick wall of a not particularly impressive miminum group size irrespective of components used and effort put in. There is nothing wrong with the cartridge design, it's the throating form which was designed to keep presures manageable with a very hot number originally designed as a long-range machinegun round.

Ken Waters also commented on this feature in his 'Pet Loads' report on the cartridge.

Laurie,
York, England

 

[boogershooter]

This was such an informative read , I had to bump it current when I went looking for it today.

 

[Cheechako]

I'm probably too late to get anyone's attention now, but I don't think size, shape, or flavor of the cartridge case makes a whit of difference. What does make tiny dots on the target are good barrels and good bullets. If all of those other things really matter, how do you explain cartridges such as the Aardvark and Wolf Pup? :

ray

 

[Forum Boss]

Ray makes a good point. For those who aren't aware ... those wildcats he mentioned have almost no neck!.

I think fine points of case geometry and neck length may be less determinative of "inherent accuracy" than people think. Look at the 6BR vs. 6 Dasher and they really both shoot equally well.

If shoulder angle and neck length aren't really all that critical, then what can we use as an empirically substantiated predictor of accuracy?

Well one magic "ingredient" may be the case volume to bore area ratio ... i.e. the "overbore index".

As a general rule, a very high percentage of the really accurate cartridge are very "under-bore" -- this applies to the 6 PPC, 6BR, and, yes the .222.

Now, mind you there are some truly overbore cartridges which have proven accuracy. But take a look at this chart. Compare the cartridges in the white zone (underbore) with those in the orange zone (overbore).

Overbore Index Chart

In my experience, once you've formed good brass, the easiest cartridge to get to shoot really well, and the most forgiving is the 30 BR. We have a friend who just broke a 20-year local club record with his 30 BR. He has shot identical scores with ammo loaded in 3 different brands of brass, and seating depths from .025 in the lands to .045 out of the lands. As an experiment, he shot a group in the low ones with 5 rounds ALL loaded to different seating depths. THAT is a forgiving round, my friends.