What makes a cartridge "inherently accurate"

[steveNChunter]

The term gets thrown around pretty loosely. When someone has a rifle that is easy to shoot accurately and isn't very picky about the load, they may tell everyone, well it has alot to do with the ______(insert cartridge of choice here) being so inherently accurate. Someone has made such a proclaimation about almost every commercial and wildcat cartridge out there at some time or another and it has caused me to just roll my eyes every time I hear "inherently accurate".

I want a scientific explanation of what makes an inherently accurate rifle cartridge, and some TRUE examples of such cartridges.

I have a few in mind that I believe qualify, but I want to hear what someone with more knowledge than me has to say about it

[Hydrostatic Shock]

I don't know and I think for some people it's just voodoo.

I've got a buddy that was always talking about 270win not being inherently accurate and the 25-06 is more inherently accurate. That was at least until we went to the range together.

[hammie]

Well, I don't have more knowledge than you and I'm sure you already know the "usual suspects".

Having said that, I think the answer to your question is: Inherently accurate cartridges are those cartridges which win matches and which cartridges the ballistic labs and bullet makers say are the most accurate from their experience. There are so many variables and unknowns with interior ballistics that this characteristic has to be determined empirically. I'm not being snarky. I just think there's no other way.

We can guess at characteristics like long necks for better bullet alignment (.222 remington), sharp shoulders, modest velocities, or shorter powder columns which idea was spawned by the Pindell-Palmisano cartridges, and which offers an explanation for the better inherent accuracy of the .308 win versus the .30-'06 springfield. However, for every factor, you can always find an exception, i.e. .300 win mag with a short neck, and on and on.

Edit to respond to hydrostatic: Hydrostatic makes a good point. The .270 has never been considered a match cartridge, but is it due to the cartridge design or instead due to the lesser availability of match grade barrels and bullets? Who knows?

[Ozzieman]

If it has 44 Special on the box.
That’s a good question. I wonder if it’s because it’s the favorite for competition shooters at the time and it gets the most work up for accuracy.
A lot can be due to bullets selection. There are so many 30 caliber bullets and 22 that it easier to match bullets to guns?
“Better inherent accuracy of the 308 VS 30-06” Did that happen because of the availability of the M1A/M14 over the last 30 years VS the 03-A3’s being used up?
I curious what the experts say to this.

[Nathan]

Good headspacing. Will the cartridge align centered in the gun every time.

Good bullets available.

Good twist rate for the available bullets.

Good brass available. Precision brass like Lapua can have much better neck consistency.

Weight of rifles it is chambered in. Heavy guns almost always shoot better.

Good reamer specs being used. Do the reamers get you close to the lands with mag length ammo. Are the reamers piloted? Are necks oversized too much.

Are available dies a good match? Both for reloaders and for ammo makers.


I think these are the kinds of this which make 1 caliber seem so much more inherently accurate than another.

[603Country]

My thought on cartridges that are particularly accurate is that the design of the case, either by design or by accident, is superior - such as the 222, 250 Savage, and 308 Winchester.

[BumbleBug]

I'm not a bench rest competitor & I don't own many rifles that fall in that "inherently accurate" category. I have an opinion but not too scientific. I think Nathan's answer is the best so far. The answer is in the platform/loading details more so than the cartridge design itself.

The implication is that a cartridge like the 6mm PPC is more inherently accurate than say a .270. If I hand you rifle & ammo to try out a 6PPC you expect to shoot a 1-hole group & if you don't, it's got to be your fault. I hand you a .270 Rem 700 & you have a different expectation. If you shoot a 1" group, you are tickled to death. With just a little preconceived notions from others a little magazine reading, a cartridge can become "inherently accurate". The truth be known, no one starts out to make a just fair PPC & loads some bulk ammo, but they do a .270.

FWIW...

...bug

[Jimro]

Shorter, fatter, bottlenecked cartridges with steep shoulders are more "inherently accurate."

The ideal expansion of any solid to gas transition is in the shape of a sphere, so the most accurate cartridges follow this trend; 6mm BR, 300 WSM, 338 Lapua.

Of course the shorter the round, the shorter you can make an action, which helps out stiffness (which doesn't count for the 338 Lapua until you start comparing it to other big heavies like the 50 BMG).

That being said, you can make long skinny rounds like a 270 Win shoot very well, and the shallow shoulders make for much nicer feeding.

Jimro

[WESHOOT2]

Shorter, fatter, bottlenecked cartridges with steep shoulders are more "inherently accurate."

I agree.

[g.willikers]

What ever is the cause, there does seem to be certain calibers that have the reputation of being inherently accurate.
In my experience, it's the .22 rimfire and the .44 Special.
It does seem that these two are extremely accurate, pretty much independent of any well made gun they are fired from.
Not disregarding the shooter, of course.

[mikld]

I asked this same question a few years ago on another forum and was told "ain't no cartridge inherently more accurate than any other". I don't buy that though. I've read that the 6mm PPC is the most "inherently" accurate round today Why? Dunno....

[JD0x0]

What ever is the cause, there does seem to be certain calibers that have the reputation of being inherently accurate.
In my experience, it's the .22 rimfire and the .44 Special.

People have different definitions for "accuracy." Personally I don't think the rounds you listed are that impressive accuracy-wise when you compare them to .204 ruger, 22-250, 17HMR which all seem to pretty inherently accurate and fairly precise IMO. I am constantly hearing reports of production .204's and 22-250's shooting MOA and better from the factory, with factory loaded ammunition, and it only improves with good handloads.

[tahunua001]

not really inherently accurate but there are some that are flatter shooting than others. you get a fatter, heavier bullet going slower and it will always lose velocity faster, drop more and be affected by wind more so there are rounds like 7.62x39 that pretty much fit the description I just made and then there is the 300 weatherby mag that is the same fat heavy bullet but propelled much faster so it is much flatter shooting and more accurate over range.

[Jimro]

you get a fatter, heavier bullet going slower and it will always lose velocity faster, drop more and be affected by wind more

This is not a true statement.

External ballistics have to do with velocity and ballistic coefficient. A small, sleek bulled like a 62gr SS109 bullet screaming along at 3,200 fps at the muzzle is going to be flatter inside of 400 meters than a 210 gr VLD from a 30-06 slumping along at 2,400 fps at the muzzle.

But that big, slow, heavy bullet will have 2 moa less drop at 1000 meters and still be supersonic.

Jimro

[603Country]

I do not believe that muzzle velocity (with a "fat", "skinny", "fast" or "slow" bullet) or bullet drop have diddly to do with inherent accuracy. I still believe that the term 'inherent accuracy' ties closely to the cartridge case. It would seem that cases like the 308 and the 300 Savage are good examples of inherently accurate cartridges. The cases are quite similar. And, for example, the 222 is considered more inherently accurate than the 223. Why would that be, if it can't be explained by minor case differences. Same powders. Same bullets. Same primers. Slightly different cases.

[F. Guffey]

“What makes a cartridge "inherently accurate""

Over and over, reloaders are instructed to Dulac the bench resters. That tid bit of information never made sense to me, it would make more sense if the instructions read “PURCHASE A BENCH RESTER RIFLE CHAMBERED WITH A BENCH RESTER CHAMBER” Then that would leave the question, what case manufacturer makes the most accurate case? So, I do not know what the questions is about, is this about cases or chambers?

Then in the 60s a shooter rebuilder purchased 500 cases from one lot, he sorted, he culled and he matches cases, some he was required to index to get consistency, anyhow, he settled on ‘about 50’ of the cases out of the 500 from one lot

F. Guffey

[steveNChunter]

the term 'inherent accuracy' ties closely to the cartridge case.

this is also what I have always thought to be true.

One of the cartridges I have always heard the term tied to is the 6.5 creedmoor. Not sure why

[Kimber84]

I suppose you've rolled your eyes at me, as the .204 I have ran multiple rounds through and have consistently seen great accuracy.

I also know of three other guns in this clambering that also perform the same way, all far below MOA. Why the .204 is so accurate, I couldn't tell you... Maybe it's the fact that a bullet moving at over 4000 fps has no other choice to go anywhere but exactly where it was pointed lol... I don't care enough to dig into the physics of it, I've just seen the results time and time again...

[steveNChunter]

I also have a couple of rifles in a common chambering that shoot ragged one hole-ers at 100 yards and have yet to see a rifle in person that shot this cartridge that wasn't at least sub-MOA with the right load. Am I saying that this certain cartridge is inherently accurate? I don't know for certain. What cartridge am I speaking of? 6mm remington.

[BumbleBug]

Well, I guess I'm an arm-chair ballistician, but reading through this thread, this is the first I've heard that the 300 savage, 6mm Remington & .204 are "inherently accurate". But I have heard that the 6.5 Creedmore is designed as a highly efficient & balanced cartridge in that caliber. As with most things, that is not the same as "inherently accurate" - I guess(?)

Just thought I'd muddy the waters some...

...bug

[boondocker385]

An inherently accurate rifle!

[Brian Pfleuger]

Originally Posted by Nathan

Good headspacing. Will the cartridge align centered in the gun every time.

Good bullets available.

Good twist rate for the available bullets.

Good brass available. Precision brass like Lapua can have much better neck consistency.

Weight of rifles it is chambered in. Heavy guns almost always shoot better.

Good reamer specs being used. Do the reamers get you close to the lands with mag length ammo. Are the reamers piloted? Are necks oversized too much.

Are available dies a good match? Both for reloaders and for ammo makers.


I think these are the kinds of this which make 1 caliber seem so much more inherently accurate than another.

None of those things are "inherent" to the cartridge.

Inherent means that it's permanent, irremovable. Combing your hair instead of leaving it in a mess might make you more attractive, but combed hair isn't "inherent", it's a process. Blonde or brunette is "inherent".

That said, I'm not convinced that there is such a thing as an inherently accurate cartridge, except to the extent that it's design makes it EASIER to get things like headspace the same more consistently.

There might be some inherent accuracy factors, I'm particularly "suspicious" of powder versus bore capacity, but then folks shoot .243Win in competition, which is quite dramatically "over-bore" and also the .308Win, which is nearly the perfect bore-to-case capacity ratio. So I don't know.

I'm quite convinced that, most of the time, these labels come from folks who are basing it on their own limited and statistically invalid experience. In other words, they had a .270Win that was accurate and a .243 that wasn't, so the .270 is more inherently accurate in their world.

[Jimro]

Brian,

All a cartridge does is provide a mechanism to make pressue which in turn propells a bullet. The case holds everything together and provides a gas seal during the powder burn. From a straight up geometric answer, the case that provides the closest to an ideal expansion chamber should be the most inherently accurate.

As with all things, all the other variables get to have a say.

The 308 Win developed a reputation for being "inherently accurate" as compared to the 30-06 in Service rifle matches, even when Garands were shot against each other in both 308 and 30-06. The only real difference between the two is case length and capacity. The trend to "shorter and fatter with steeper shoulders" continues because it is easier to make those cartridges consistently accurate.

Is the 308 inherently accurate compared to the 30 Benchrest? I don't know the answer because the 30 BR is pushing lightweight bullets through slow twist barrels. The 308 Win has too much case capacity to ballistically match the 30 BR (although you could make a good case for heavier bullets with only a slightly faster twist) to see if you could find a difference.

But honestly, I know that most rifles, no matter the cartridge, are better than most shooters with an appropriate load. With the wrong load even a precision rifle won't group (4 minutes from an AI sniper rifle with milsurp ball, 12" groups from my Savage Tactical with some Fed 180gr soft points).

Jimro

[Brian Pfleuger]

Originally Posted by Jimro

The 308 Win developed a reputation for being "inherently accurate" as compared to the 30-06 in Service rifle matches, even when Garands were shot against each other in both 308 and 30-06. The only real difference between the two is case length and capacity. The trend to "shorter and fatter with steeper shoulders" continues because it is easier to make those cartridges consistently accurate.

Yeah, that's one of the things that makes me suspicious that case capacity versus bore size is one of the "inherent accuracy" factors, if there truly are such things.

Originally Posted by Jimro

...the case that provides the closest to an ideal expansion chamber should be the most inherently accurate.

Ok, but what IS the "ideal expansion chamber" and is it fixed or variable, depending on one or more of things like bore area, barrel length, bullet weight, etc., etc....

[Jimro]

Brian,

Ok, but what IS the "ideal expansion chamber" and is it fixed or variable, depending on one or more of things like bore area, barrel length, bullet weight, etc., etc....

In terms of accuracy? I haven't the foggiest. But I assume that it will depend on the distance you are measuring accuracy at, which means it is a variable, and not a fixed value.

http://www.6mmbr.com/30BR.html dominate 300 and under.

Right now the big 7's are dominating F Class http://www.6mmbr.com/7mm284.html

But either way, shorter, fatter, steeper shouldered cartridged have been replacing skinnier longer cartridgets with shallow shoulders. I mean if it were solely about ballistics there should be no accuracy difference between a 300 H&H and a 300 WSM. Clearly there is something going on there, same as it was for the 308 and 30-06.

Jimro