"Intrinsic Accuracy" of a Cartridge

[whitebear]

I've seen this phrase used several times in reference to the .32, .40 (IIRC) and others, both pistol and rifle, and it has set me to wondering (never a good thing...):

What actually influences the "intrinsic accuracy" of a cartridge? How is this measured? Scientifically, objectively, or from non-documented long-term experience? Why doesn't accuracy depend more on the firearm than on the cartridge? What is the airspeed velocity of a swallow? (Wait, never mind that last one...)

Thanks in advance for the education!

 

[Jeeper]

I dont know about pistol loads but I believe that there are rifle cartridges that are intrinsicly accurate. The 6mppc for example is such a widley used cartridge in Benchrest eventhough there are other cartridges taht are almost identical in velocity. Most accuracy is a combination of the gun and shooter.

 

[Carbon_15]

Some rounds have it some dont. When a particular cartridge is fired through a fixed, barrel blank in a labretory, that is the most accurate it will ever be. Absent the imperfections of a traditional gun and weakneses of a shooter, the bullet is free to perform to its potential. Kinda like a Ransom rest for the BULLET. No matter how well the gun is made and how great the shooter is, the round will never get more accurate than it is in the lab. some callibers show better performance in this type of testing than others. The 2 most stelar performers are the .45ACP and 9mm..2 rounds with nothing in common. On the other hand, few .40's are more than "Combat Accurate". What gives a bullet more intrinsic accuracy, thats a mystery.
Be carefull not to put to much into intrinsic accuracy. In most cases, We are talking about millimiters here. The thing to remember is that an intrinsicly unaccurate cartridge will be magnified when you add in the imperfections of a real repeating arm and shooter. A more accurate round tends to be more forgiving of gun and shooter...show me an innacurate .45..from the Lorcin to the WWII rushed production 1911's a Thompsons, they are all more accurate than their similar-quality counterparts in other calibers.

 

[CastleBravo]

Anyone who thinks .40S&W is inherently inaccurate never fired it from a S&W 610 Classic 6.5".

There is so much variation in accuracy depending on the bullet/load/gun combination that it is probalby impossbile to figure out for sure if a particular caliber is inherently more accurate than another.

 

[Carbon_15]

My post was not ment to be a slam to the .40 or any other for that matter. But the fact remains, when you take the gun and shooter out of the equation, and use a carefully controled barrel blank held in a ridgid mount w/ electronic fire controle, you simply get less accuracy with the .40. There are good performers and not as good..the .40 is just the one that stands out. This is not to say a .40 cannot be fabulously accurate...we are talking about millimeters and fractions of an inch here. What it boils down to, is if you are using a perfect barrel blank under perfect conditions, some bullets will all go through the exact same hole, some will make larger more ragged one hole groups. That is all intrinsic accuracy is about.

 

[James K]

Hi, Carbon 15,

Just curious, but have you actually done the tests you cite in regard to the .40 S&W or any other cartridge?

I agree that some elements of the .40 S&W design might limit accuracy (e.g., the short bearing area), but there are so many variables that I don't think it is possible for anyone to say that "a caliber" is or is not accurate. For one thing, is there really a "perfect" barrel? Would all bullets and loads be inaccurate or only some?

Some calibers are very accurate, but mainly because they have had a lot of time and money spent to find the right combination of bullet, load and barrel characteristics. Some calibers are limited by external factors. For example, a bullet with good ballistic coefficient might not be practical in .30-'06 if it causes the cartridge OAL to exceed the magazine length.

FWIW, I never connected the word "accuracy" with the .25 ACP until I saw some 1/2" 25 yard groups fired in a 22" barrel with it. It won't be on the bench rest circuit soon, but that darn little round will shoot if used in something better than the usual tiny pistols.



Jim

 

[Chop Farwood]

I think "intrinsic accuracy" basically refers to a cartridge design that is a little more fault tolerant than most. Rate of twist is not critical for good performance, throating and crown can vary somewhat, yet the cartridge will still generally perform well under varied conditions. But that's just my guess.