an accurate load on an accurate gun shot by a good shooter will make a cartridge accurate.

The latent potential for accuracy must be there. If not, there is really nothing a barrel nor a smith can do for it. They may make it shoot on the smaller limits of bad but they aren't going to make a .222rem out of a .225win.
What makes one cartridge more accurate than another, all things being equal, is still a mystery, poorly understood.

Beeman, you obviously have never shot an accurized 225W ! It will shoot with any of the larger 22 chamberings, as it is quite similar to the Wasp. When the 225 was first introduced, it was considered a "super accurate" cartridge. Turns out, it was largely attributable to the super uniform brass made by the brand spanking new dies at the ammo plant.

If the question is what makes a cartridge design accurate, then we can ignore the standard requirements of an accurate rifle: ignoring a good barrrel, put on right, with super uniform bullets, brass, primers and accurate charges of an appropriate powder.

An accurate cartridge needs consistent ignition. That, after everything is said and done, is what makes one bullet vibrate the barrel the same way and leave at the same point in the vibration cycle, at the same speed as the next bullet fired.

Consistent ignition requires that all the powder is ignited the same way, every time. Long, straight wall cartridges (say, 35 Whelen), have a hard time doing this, because the bullet starts moving down the barrel too early. Powder starts moving down the barrel before it is hot enough to ignite. Shorter cases (be it a PPC or a pistol case) ignite the powder fromt the flash hole all the way to the base of the bullet as the primer goes off. Much less powder goes down the barrel before being warm enough to ignite.

The reason you need fat cases, IMO, is to keep the powder column short enough to ignite all the way to the base of the bullet. If you need more capacity, you add it in the width of the cartridge, not in the length.

Of course, you need enough neck tension to keep the primer from moving the bullet (if the primer moves the bullet, this would introduce another variable). That is why a SMALL flash hole is used in the PPC case: it keeps the violence from the primer lower, while still giving excellent ignition. As a result, bench rest shooters can use very little neck tension and still get good ignition. JMO, Dutch.

It's very interesting to observe how this myth the short, fat case is spreaded by writers, manufacturers and a lot of nice people!

After all, we the shooters really love this kind of talk!

But, science is science, no more no less...

And, so far, nobody presented a real reason for this wonderful design feature and it's incredible characteristics !

Just an example, someone wrote many years ago, that a simple ratio between diameter and weight (Sectional Density) is a feature that implies penetration.

Well, just very recently this myth (mouthed from father to son for years) is showing that there is no statistical correlation between penetration and this magical ratio!

Many recent studies are showing the same for the short & fat, but since I'm as open minded as everybody I'm still waiting for the study to prove their point, not just the stone-carved phrease in every article written by man respected authors "... the short and fat case promotes efficiency and accuracy and prevents hair loss..."

Regards,

old firing line archived thread on most accurate cartridge



As the late great Gale McMillan wrote on 9-11-99, "The smallest group at 100 yds ever fired in competition and holds a world record for 20 years is held by a 222. The group is .009 center to center.. If you are ever in Phoenix drop by as we have the target and rifle on display in the shop."



As Randy Ketchum, gunmsith who does some benchrest work, told me, "~ The 6mmppc is accurate becuase of the great brass available and how carefully it is prepared. The .222 is not as good as it used to be becase the Win brass is not as good as it used to be.~"

I have been reading a lot of topics on the board dealing with accuaracy. I get the impression that cartridges with short, fat cases (similar to the 6mm PPC), with small flash holes, and small rifle primers, have the potential for better accuracy. Are there any other factors that contribute to accuracy? Can someone suggest a book that explains why these characteristics work better than others?

Big recoil is hard to absorb consistantly.

The .222 can't buck the wind as well as the bigger 6mmppc, but the 6mmppc does not have enough recoil to matter.

I think there is about 2 foot pounds of recoil on a 6mmppc in benchrest competition.

Compare that with 20 foot pounds from a 30-06, and the difference in accuracy with same weight rifles is not due to the shape of the cartridges, but the size.

Theories about as to what makes cartridges 'tick'. Part of it has to do w/ the case design i.e. short fat generally works a bit better than long skinny for 'absolute' accuracy. Generally I think the theory has to do w/ better (however you want to define that) ignition of the powder column, etc. I think the other part of it has to do w/ the bullet selection for the task at hand. You see the people shooting 'group' and 'score' BR @ 100, 200, 300yds predominantly shooting flat base bullets, and short/fat cases, and getting some phenomenally small groups. But I doubt most people who want to win at say, 1k BR, are going to even touch a flat base bullet or a 6mm PPC (maybe a 6mm BR). Techically more 'perfect' doesn't matter if it doesn't make it to the target supersonic. Etc. and so on. In the end, the sport isn't shot in a vacuum, and the most deciding factor is the nut behind the trigger

YMMV,

Monte

elkhntr,

Short, fat cases are roughly shaped like a sphere. A sphere is considered a more efficient shape. Industry often uses sphere shaped vessels to mix/combust chemicals. Spheres have less surface area for a given volume, this why critters up north have evolved short, squat shapes--less surface area, less heat loss.

So, if we think of the inside of the case in terms of longitude (down the axis of the bore) and latitude (towards the sides of the case), the primer ignition can potentially "reach" more powder, and the powder is able combust towards the front of the powder charge (longitude) as well as towards the outside edge of the powder charge (latitude). Keep in mind, an inherent problem in cases is ignition is in the BACK of the powder charge, some of the powder is being blown forward (down the barrel) before it is ignited.

The Holy Grail is complete ignition/cumbustion inside the case. Benchresters are claiming they think some loads may be able to achieve complete ignition (but not necessarily complete combustion) inside the case. This theoretically acheives a quicker rise in the pressure curve (another goal in efficiency/accuracy). There is also the idea that this may reduce the oscillation (barell whip) at the muzzle. Pressure (and the pressure curve) plays into this efficiency/accuracy thing as well.

Small primers are easier to make more consistent (less primer charge) small flash holes produce a more consistent flame. Consistency in all the aspects of interior ballistics is THE Holy Grail (but I suspect you already know that).

Hunting weight cartridges tend to work against these things. The 308Win comes the closer to this idea, the new short mags may be better, but the 30.06 and 7x57 cases still compare (and compete) well in the efficiency department. Over the years I have taken more of a wait and see approach to some of these things. Large case capacity (in relation to the bore) require long(er) barrels. The reason? A whole lot of that powder is headed down the barrel before it is ignited and/or combusted. This is one of the primary reasons why the mags take 2%-4% more powder charge to achieve 1% increase in velocity.

Casey

In my opinion, what makes a cartridge accurate is a good barrel put on by a very good gunsmith. FWIW, Dutch.

Aside from short and fat, there is another aspect to recoil that is important. The more powder used and the more energy released, the more the rifle itself has to cope with. Small things can change as heat increases and the optics get beat up. Not only the barrel but the front of the receiver and bolt face heat up.

These metal parts and fittings are NOT the same dimensions and are stressed differently as heat increases. Cooling back down to some base level of heat does NOT mean that everything as the same as it was before the heat excursion occurred. So, the less heat and mechanical stress the better.

Now, the effects of heat and mechanical stress can be mitigated by weight, materials and design but these solutions require precision and cost money. The average shooter who wants to shoot 1/4 inch groups @ 100 yards is pretty much limited to .224 and 6mm rounds suited to the task.

1) Accurate bullets, without them, everything else is mute.
2) Quality barrel, a consistant bore is the starting point.
3) Quality gunsmithing, this may be more important than the barrel quality, but top smiths start with quality componets. Unless the chamber is accurately cut to the bore, the crown cleanly cut, end everytying assembled on centerline of the action axis, you don't have the needed foundation.

I haven't mentioned the cartridge yet, as it is sort of a horse/cart relationship, ie the accurate guns are built with the accurate cartridges.

Now to the cartridge itself, what is desired is a consistant cartridge, ie, if the temperature changes 5 deg, you don't want the round to fall off it's face. The Rem BR case, which is short and fat, and w/ a small flash hole has never consistantly shot as well as the PPC case. While it may have the potential to be more accurate in certain conditions, it hasn't proven to be as reliably accurate as the PPC's.

So long as you aren't competing, and stay away from the extremes, ie long skinny cases, or real small ones like the hornet, then a good smith can make any of them shoot very accurately. The challenge with the hornet and other small cases is throwing consistant powder charges.

I've found The Ultimate in Rifle Accuracy to be a pretty good read on what makes a rifle accurate.