“Inherent accuracy” is to the ammunition world what bigfoot is to the natural sciences: elusive, controversial, and possibly (probably) a myth.
A tremendous amount of online ink has been spilled on the subject. In this thread on The High Road forum, gun owners rattle off a variety of cartridges that, in their opinion, are inherently accurate. The .243 Win., .222 Rem., 6mm PPC, 6mm BR, .300 WSM, and the 7.62x39mm Savage all make appearances.
Keyboard warriors aren’t the only ones who have weighed in. Writing for Field & Stream, gun writer David E. Petzal explains that cartridges with less powder, a steeper shoulder angle, and small rifle primers lend themselves to better accuracy. As for the most inherently accurate cartridges, Petzal doesn’t hesitate: the 6.5mm Creedmoor and the 6mm PPC.
Why do these attributes lend themselves to accuracy? It’s not entirely clear. That’s why we went to the experts to help us shed light on this elusive controversy.
The Experts
Seth Swerczek is Hornady’s Communications Manager, but he worked for the ammo maker as a product technical representative and a ballistics engineer. He is also an active competitor on the precision rifle circuit.
Tommy Todd is the Chief Ballistician for Sierra. In the last 30 years, Todd has worked in every department at Sierra in everything from raw material acquisition to bullet forming to testing. He’s competed in rifle competitions such as the HiPower Silhouette, Across the Course (HiPower), Long Range Benchrest, and F-Class.
Cutting to the Chase
Based on our conversations with Swerczek and Todd, some cartridges do have certain attributes that produce better accuracy. But these attributes are far less important than most people think. The most important factor is how the cartridge interacts with the chamber. Well-designed chambers will be more accurate, no matter the attributes of the cartridge.
Diving Deeper
I should say at the outset that when I say, “inherent accuracy,” I’m referring specifically to short-range accuracy. Long-range accuracy is determined by the velocity of the projectile and the bullet design, and we all know that long, high-BC bullets fly flatter than short, stubby bullets. For this Fact Checker, I’m sticking to accuracy within 100 yards or so.
Here’s what I found.
When a manufacturer sends a cartridge design to SAAMI for approval, they send a chamber design as well. Ammo makers use the cartridge specs and gun makers use the chamber specs to ensure that the firearms produced can safely fire that specific cartridge. The relationship between the cartridge and the chamber is the most important contributor to “inherent accuracy” – or lack thereof.
“It doesn’t necessarily come down to the cartridge design,” Swerczek told me “There are some things that typical match-type cartridges have, but the most crucial thing is the chamber design. The cartridge-chamber interface is supremely important when we’re talking about ‘inherent accuracy.’”
Swerczek explained to achieve good accuracy, a bullet must enter the rifling of a barrel perfectly straight. Even the slightest variation will affect a shot’s point-of-impact. Whether a bullet enters the rifling straight depends on the measurements of the chamber and, more specifically, the free bore.
“The diameter and angle of the free bore is critical,” Swerczek said, referring to the unrifled portion of the barrel. “Because if it’s too large, as that bullet is coming out of the case mouth, gravity is working. It’s got more of a chance to enter that rifling at a slightly off angle, and you never get that back.”
Todd agreed. The relationship between the chamber throat configuration and the average bullet shape utilized in the cartridge is one of only two factors the Sierra ballistician mentioned as influencing inherent accuracy.
A cartridge/chamber design with lots of play between the free bore and the bullet will tend to shoot more inconsistently than a tight bullet/free bore configuration. The .300 Winchester Magnum, for example, has a free bore diameter of 0.315”, which allows for 0.007” between the bore and the 0.308” bullet.
“The .300 Win. Mag. is an atrociously designed chamber, per the SAAMI specs,” Swerczek said. “The tolerances that that chamber allows are laughable.”
Custom-built chambers can correct for this, of course. Swerczek said that the .300 Win. Mag. can shoot like a “house afire” in a rifle that was built with a match-grade reamer.
“It all comes down to the chamber and cartridge and bullet relationship,” he concluded.
This is why some cartridges earn a reputation for accuracy. It’s not really the cartridge—it’s the combination of the SAAMI-approved, factory production cartridges and chambers that either shoot well or don’t. A custom rifle shooting hand loads can be dead-nuts accurate in almost any shouldered cartridge.
(If you want to do your own digging, you can find new and old cartridge/chamber designs on the SAAMI website here.)
Of course, there are some cartridge attributes that lend themselves to accuracy. Todd said that, as a general rule, cartridges with shorter, larger-diameter powder columns shoot more accurately than longer, narrower powder columns.
“The reason for this seems to be more consistent burn of the powder which translates to better external performance of the shooting platform,” Todd said.
Swerczek reiterated this point and said that straight-wall cartridges can be especially difficult to ignite consistently.
“That tall powder column can be difficult to get ignition consistency. Typically, with a straight-wall cartridge, you see higher velocity extreme spreads, which usually occur because of inconsistent early peak pressure,” he said.
Swerczek also mentioned that balanced cartridges tend to perform better than overbore, super-fast cartridges. The .308 Win., for example, doesn’t boast a great chamber design, but its size and velocity are balanced nicely, and shooters have had great success with the cartridge.
Interestingly, and in contradiction to the accepted wisdom on this topic, neither expert mentioned the shoulder angle as having a consistent impact on accuracy. The height of the powder column, the presence of a shoulder, and the relationship between the cartridge and the chamber seem to be the most important factors.
Final Verdict
There are some cartridge/chamber designs that shoot more accurately out of factory rifles, so it’s understandable why some cartridges earn a reputation for accuracy. But that accuracy has little to do with the cartridge itself. A well-designed cartridge/chamber combination will shoot almost any round accurately, which is why I’m calling the “inherent accuracy” claim partly true.
Never had the financial resources to have a custom, tricked-out rifle. But, I found that with careful hand loads, I could greatly improve on the accuracy of a given cartridge. I also found that some cartridges benefited more than others from “tweaking.” Unless you’re a competition shooter or long-range hunter where extreme accuracy is necessary at extended distances, I don’t see the need for wringing-out the absolute nth-degree of accuracy from a cartridge/gun combination.
I feel that i can say without contradiction, that with any calibre of ammunition, David Haehl, age 50, will shoot with more accuracy than Earl Haehl, age 77.
The argument about inherent acurracy has been argued as long as i have been around. An we have argues in an atmosphere of opininion rathe than fact. t may be time to give this crap a rest.
The first three paragraphs tell me everything I need to know about the following “online ink” as the motivation seems to be to stomp toes.
As to the rest, which I did read out of fairness, other than to follow my Grandmother’s maxim on comportment… It seems to argue with itself.
Todd.
Without dredging up the issue of “accuracy” vs “precision”, a useful illustration of the importance of cartridge/chamber interaction, is the .223 Wylde vs a standard 5.56 (NATO) chamber. The same platform will shoot more precisely with the Wylde chamber specs (all other things being equal). I agree with Big Al that most “out-of-the-box” weapons will shoot more precisely than most people can… but there are a variety of considerations that affect cartridge precision.
Well, let’s do mention longer necks as useful in holding bullets concentric to the bore. And also throw in purpose designed cartridges for bolt actions like PPCs and the 222 that Gale McMillan held the BR records with. Also shot .32” at 200 in a match and came in 8th vs. BR competitors, none of whom use factory barrels or ammo…just Fudd guns and FB bullets.
Can’t help but wonder how the .222 Remington made the “inaccurate” list. My simple CZ 527 American prints .25 inch groups all day with factory ammo. just curious.
IMHO.
Jim says…, “If the above is true then any chambering can be made to shoot lights out, and the bench rest world would see dozens of chambering on the firing line.
But all you’ll ever see are 6mm BR, or PPC and their variants.”
Makes sense that almost any cartridge COULD shoot “lights out” if everyone had custom made barrels or builds from “custom” shops.
Most pick something ‘off the rack’. So you get what you get and buy what is known. So you buy a 6mm variant.
IMO. I could be wrong and would like to hear other opinions. I am probably wrong! Ha Ha Ha!
Jim says…, “If the above is true then any chambering can be made to shoot lights out, and the bench rest world would see dozens of chambering on the firing line.
But all you’ll ever see are 6mm BR, or PPC and their variants.”
Makes sense that almost any cartridge COULD shoot “lights out” if everyone had custom made barrels or builds from “custom” shops.
Most pick something ‘off the rack’. So you get what you get and buy what is known. So you buy a 6mm variant.
IMO. I could be wrong and would like to hear other opinions. I am probably wrong! Ha Ha Ha!
I tried running a Palma match chamber 308 and a custom 30-06 at 600 yards and 100 yards. Just money poured down a drain.
But i think the article should have been titled “Characteristics of Accurate Cartridges” I would have no issue with the content for the most part. (i now shoot a 6DX, a 6.55-284, and a 30BR.)
If the above is true then any chambering can be made to shoot lights out, and the bench rest world would see dozens of chambering on the firing line.
But all you’ll ever see are 6mm BR, or PPC and their variants.
The fallacy in your argument is that it forgets the people in those competitions are humans and are subject to peer pressure, and that they are experts in cartridge design and its interactions with the chamber, which I suspect is very rare. They are shooters, not engineers.
The other factor to consider is the bullet Ballistic Coefficient. 6mm and 6.5 mm are in the sweet spot to have heavy for caliber (Long) projectiles that with the right rifling twist are the best offered. Put that with the custom chamber and that is probably about a good as a it gets.
In the world of shooting, partially true means true. I won’t tear apart the article, which I could. I’ll just say that there are a million things that effect your shooting score (or hunt). Therefore, any advantage in shooting accuracy is an advantage and that’s reason enough for most of us to gravitate towards the inherently accurate cartridges.
Perhaps you should have put emphasis on ‘Inherently’ as the article points out that there really AREN’T any.
But it seems you don’t believe that to begin with despite the article.
45 years of shooting and reloading, and frankly I have found it’s more about the gun and LOAD than the cartridge itself.
IMHO, the average cartridge in the average gun shoots better than most people can, and careful handloading can really help. but only goes so far.
It isn’t about the singular component, it’s a system. Cartridge, load, and gun ALL play a part, and no ONE component is the end all, be all of accuracy.
Yes, there are always exceptions to the Rule, but placing ones faith in just the one component will often lead to disappointment.
It seems you are missing the point of the article. There really aren’t inherently accurate cartridges in terms of the common thought. There are inherently accurate cartridge-chamber combinations. Think about the old, wallered out AK47s and 7.62×39. Bad reputation for inaccuracy, but it has nothing to do with the cartridge. It has everything to do with the wallered out chambers in the AK.