“Inherently Accurate” round

[TXAZ]

Overheard another interesting discussion at LGS, about “Inherently Accurate” rounds.
One point was it was solely the shape of the bullet.
The other was it was mainly the barrel and forces applied to the bullet.

I expect it’s a “total system solution”.

Any wizards out there with a learned perspective?

 

[44 AMP]

You are closest with the "total system" idea, but there are limitations to that answer, as well.

The term comes to us from bench rest shooters, who discovered that shorter powder columns (usually) produce less shot to shot variation than longer ones. Consistency plays a big part in accuracy.

So, a round designed with a shorter powder column is considered to be "inherently" more accurate.

Along with this is the shorter case rounds often mean the rifle is "stiffer" at important places, and again, that means less variation possible.

These are the kinds of arguments often used when someone says the .308 is "inherently more accurate" than the .30-06. (for one example)

Reality, on the other hand is somewhat different. Inherently more accurate is a numbers thing, as well. If you look at enough rifles (hundreds for example) you may find that more of them in caliber A are more accurate than "the same" rifles in caliber B, and therefore people claim caliber A is "inherently more accurate" than caliber B. Numbers prove it, right???

Except that, the numbers only apply when you are looking at LOTS of rifles, and don't mean squat when comparing any two SPECIFIC rifles.

Every rifle is an individual in many aspects, and you are right about it being the total system that matters most.

 

[TXAZ]

Thanks 44 Amp, appreciate the feedback. I love listening to these guys, some really understand the 'art of the rifle', others maybe not as much ...

 

[WillmannJohn]

Ah...the things you hear at the old local gun store.

 

[jmr40]

There are several things that come together. As stated short fat cartridges with similar powder charges tend to be more accurate than longer cartridges because the powder burns more consistently and more efficiently. You also get more velocity with less powder and less recoil. The 308 vs 30-06 is a good example where there lots of data. But the same is true of many others.

The shape of the cartridge including the angle of the shoulder is also a factor.

This doesn't mean that every 308 is more accurate than every 30-06. But all things being equal it is easier to get a 308 to shoot accurately than a 30-06. And you need a pretty good trigger puller to take advantage of the difference.

 

[reteach]

I have read in a number of places that the .32 S&W Long is an inherently accurate round. There is even a Benelli semi auto built for the round for serious target competition. So please educate me - How does that round fit with the shorter powder column description?

 

[Scorch]

Inherently accurate has to do with many factors, so benchresters started noticing that some cartridges were more accurate than others all other things being equal. Harry Pope thought the 32-40 was the "ne plus ultra" of accuracy. The 222 Remington enjoyed the reputation for many years. 22 PPC, 22BR, 22 Waldog, etc, all are moderate capacity cases with moderate powder charges that achieve moderate velocities. Some have small primers, some have different shoulder angles, some have short-fat or long-tapered configuration. I have never spoken with someone who could absolutely state which cartridges would be inherently accurate just by looking at the data. There are lots of combinations combined: some work, others don't.

 

[FITASC]

6mm BR is inherently accurate. Along with the parent 7mmBR, the idea of a short/fat cartridge being more accurate than others seems to have been proven over time by those who shoot benchrest matches.

 

[44 AMP]

So please educate me - How does that round fit with the shorter powder column description?

because (in part) its already short. The case length is only 0.93". It's called the "long" because it is 0.3" longer than the .32 S&W case which is 0.61"

It is considered an "inherently accurate" round because you are typically dealing with fairly soft lead bullets at low pressures and speed which allow the bullet a good "grip" on the rifling. Also, generally speaking you find it in guns who's sights don't move in relation to the bore, unlike something like the .32ACP which shoots a jacketed bullet most often from a semi auto where the sights and barrel are not fixed together.

6mm BR is inherently accurate. Along with the parent 7mmBR, the idea of a short/fat cartridge being more accurate than others seems to have been proven over time by those who shoot benchrest matches.

I won't argue this, it sure is what seems to be the case. I will, however note that benchrest shooter generally shoot benchrest rifles and what applies to them doesn't always apply equally to other classes of sporting rifles.

 

[Tony Z]

The gun club I belonged to, in the town where I was raised (moved over 30 years ago), had a self-proclaimed expert that was always extolling the 6mm Remington (not BR!) over virtaully any and all other calibers. He had no evidence, other than what he read, but, there was some there there!

Maybe there is efficiency in the calibers in the quarter inch diameter range? But as 44 Amp has said, there is a difference between benchrest shooters and hunting class shooters - both gear and person.

 

[Nathan]

I get really confused about “inherently accurate” and other gun store statements about accuracy.

First we need to define what causes accuracy. To me, this is really tough, but I start with short range accuracy. For a modern rifle, I define that as 100 groups, specifically 5 shot groups shot off a benchrest by a perfect shooter. This allows wind and drop to be ignored. Let’s ignore the rifle factors for this post. So, what factors of the cartridge. IMO, those main factors are bullet alignment to throat, consistent bullet release point, bullet fit to bore....

From a mathematical point of view, we are aligning a cylinder within a cylinder. Using the concentric cylinder model, with a standard radial gap, the longer the round, the less misalignment is possible. Hmmm.

In addition, with axial force like the push feed ejector, the more case taper(shoulder and body) the better.....so something like 30’06 should be best.

Looking at government designs, they seem to buy into this...223, 30’06, 50 bmg.

So this gets the case lined up....what about bullet to case alignment? Seems like I want a case that has good neck to bullet engagement. Again thinking about concentric cylinders. I’m not sure what is best, but when I look at 222 Rem, 6 ppc, 6 Dasher, 6.5 creedmoor, they all have neck length to diameter ratios .98-1.4. While 223 Rem which is generally not as easy to get accuracy from is 0.9.

Then there are the “consistency of bullet release point” factors. This has a lot to do with consistency of burn, case fill, bullet fit to bore, recoil stroke, etc. Really, case fill, land erosion and oal consistency are key here. First land erosion....it has been roughly determined that steeper necks reduce throat erosion with powders that have that issue. So, let’s assume 35-40 degree shoulders are best. Over 40 becomes really hard to form and resize consistently. Case fill.....all I can say is some cases when matched up to available powders, tend to have fill percentages from like 85-95%, 95-105%, and even 105-115%....I believe rounds in the middle to high range are best. High is ok because most rifles require you run rounds long to get anywhere near the lands.

So, what does this tell me.....a round with a long case body, 35-40 deg neck, neck length to bullet dia ratio of ~1.1 and case fill of 105% is best....in addition, it needs to have a variety of accurate bullets/brass available...

So, 222 Rem, 6x47, 6mm creedmoor, 6.5x47, 6.5 creedmoor, 6.5x55, 280ai, 300 Norma....I’m sure there are more.

 

[Bart B.]

Few, if any, cartridges are perfectly centered in the chamber when fired.

Once you've learned what external forces position the cartridge when it's fired, you'll know why.

If they're repeatable from shot to shot, best accuracy happens.

Searching for benchrest match results will show the most popular cartridges for best accuracy.

 

[TX Nimrod]

The gun club I belonged to, in the town where I was raised (moved over 30 years ago), had a self-proclaimed expert that was always extolling the 6mm Remington (not BR!) over virtaully any and all other calibers. He had no evidence, other than what he read, but, there was some there there!....

When Ed Harris was with Ruger he compared the 6mm’s accuracy to the .243 Win. He tested 12 identical Ruger rifles in each chambering (I’m not certain of the exact number, it may have been six of each for a total of twelve. The important part is that he used more than one or two rifles). The average .243 was significantly more accurate than the 6mm. Harris concluded that the reason was due to the 6mm Rem chamber having a 3 degree leade compared to a 1.5 degree leade for the .243 Win. After making a 6mm reamer using the .243 Win leade the accuracy of the 6mm improved markedly. As I recall he wrote it up in Handloader magazine in the mid/late 80s.

The takeaway here? Cartridge shape is not the only contributor to ‘inherent accuracy’.



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[reinert]

what "inherently accurate" means to me...

When I started reloading 40 years ago now, I was working construction with a bunch of guys who all reloaded ammo, hunted big game, hunted varmints and were quite knowledgeable on just about all aspects of shooting and reloading. Since those days, I've always considered myself truly fortunate to have been able to work and "hang" with those guys, as their info and advice on guns and shooting was priceless. They were mentors all, and got me started right on this continuing ammo reloading journey.

One of the guys I worked with had a Remington M788 in .222 Remington. When he showed it to me, he said, "This rig is inherently accurate." I asked him what does that mean? He said the rifle and ammo shot tiny little groups, and was hell on coyotes and fox (he kept it in his pick-up; his knock-around rifle). He also said that a round that had the reputation of general, good accuracy no matter who you talked to, was an "inherently accurate" cartridge (the .222 Rem was certainly one of those; still is). The .270 Win. was quite popular back then, too.

My first good bolt action high powered rifle was purchased back in those days, and since I wanted something I could varmint and big game hunt with, all my buddies pretty much agreed to either get a .243 Win. or a 6MM Remington. The consensus "nod" was the 6MM, because it had a bit more case capacity and was "inherently accurate" (then the discussion got into the .244 Rem, the .243 and the 6MM Rem., r.o.t.s, bullets, seatings, neck, full length or partial case sizings and etc.; I surely won't go there, now...). So, I bought a brand new Ruger M77 in 6MM Remington, in 1979, for 180 bucks (and I still have it). I wasn't reloading yet, so I bought factory Winchester and Remington 80 and 85 grn. ammo while starting to acquire reloading equipment. That rifle shot that factory stuff unbelievably well, and I understood what the "inherently accurate" term meant, at least for me and my Ruger. Once I got my own start on reloading, I settled on a load using the 87 grn. Hornady S.P. for the bullet, and it's what I still use exclusively for that rifle's load, because it's "inherently accurate" in my M77.

As an aside here, I killed my first elk with that rifle, using a factory 100 grain Remington Core Lokt S.P. bullet. They shot well in the Ruger, too.

 

[stagpanther]

What does "inherently accurate" actually mean? I would call an inherently accurate cartridge as one that typically shoots well regardless of the rifle and/or charge/bullet used. Does that sound about right?

 

[44 AMP]

What does "inherently accurate" actually mean?

What it actually means is "I've made up an impressive sounding term to sell guns and ammo..."

I contend that there is no such thing as "inherently accurate" and that it depends on both the design AND the execution of that design of the gun and ammo in your hands. If ANY of these factors is less than the best possible, "inherent accuracy" goes out the window and is revealed for the myth that it is.

EVERYTHING matters, some things more than others but it all plays a part.

I am reminded of the story about the guy who had a Steyr SSG, in the Philippines. The SSG is widely regarded as an accurate rifle. The .308 Winchester is one of those cartridges often referred to as "inherently accurate".

The guy was getting paper plate size groups @100m. So much for "inherent accuracy", right?

Here's the thing, the fellow was shooting Philippine Army "surplus" ammo.
When a friend convinced him to try Federal Match ammo, he got MOA/sub MOA groups.

Inherent accuracy is a potential, not a given fact. How well done (manufactured) the stuff you are shooting (gun AND ammo) is what determines IF that potential can be realized.

 

[5whiskey]

I will also throw the nod that projectiles with longer bearing surfaces tend to be more “Inherently accurate” than most projectiles with a shorter bearing surface. Hence, calibers that favor this trend, while still keeping recoil manageable, also tend to be more “inherently accurate” imo than calibers that do not. In other words, small bores. There are other advantages, such as sectional density and BC, which also contribute to an increase in favorable internal and external ballistic characteristics. Further still, the recoil tends to be more favorable for accurate shooting.

Many have mentioned shorter powder columns being more “inherently accurate.” I do not dispute this as I simply don’t know. My question is... was the concept or reasoning behind the mostly out of favor WSSM cartridges? I have not heard of them being wildly accurate, but I also believe that it may be because many people who bought into them weren’t accuracy shooters in the first place.

 

[old roper]

When I started BR the 222 was on the way out and 6ppc was the one to shoot and none of those rifles where factory. You buy accuracy is what you do.

Ask Bart what his match rifle cost and who build them.

 

[Nathan]

Yea, once you jump to BR rifles, the inherent accuracy question really goes off the rails.

These guys fit cases, dies and chambers exactly to each other. The bullets are often in the lands to start. Bullets are custom, cases perfectly fit, powder charges weighed to 0.01gr, bullets seated to near 0 runout.....

No feeding, no dropping in the field, no magazine considerations, no reliability factor....just not reality for most rifle shooting.

 

[TX Nimrod]

Yea, once you jump to BR rifles, the inherent accuracy question really goes off the rails....

Really? Then why did BR shooters change to the then-difficult-to-acquire 6 PPC case rather than keep the easy to find .222 case? Why do high power across-the-course shooters prefer the .308 over the .30-06? Why did many 1000 yard shooters eschew the big magnums for smaller cases?



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