Cartridge accuracy....

[Eric Leonard]

Cartridge efficiency is what can make one cartridge more accurate then another.
When a smaller capacity cartridge, can produce near equal velocities for a given bullet weight, it is more efficient, hence; more inherent accuracy.

Cartridge Efficiency:
(Bullet Weight * .5) * (MV ^ 2) / (Charge * Joules per grain) / 98000 = % of efficiency
Note:: (kJ/kg / 15.4324 = Joules per grain)

Examples:
6Dasher:: 105-VLD <> 3000-fps <> 32.5 of RL-15 = 57.4%
243-Win:: 105-VLD <> 3000-fps <> 44.5 of H4350 = 44.9%

44.5 H4350 in a 243 Win with a 105 VLD would be pretty hot by my experiences with that combination,,

 

[gunsandgunsmithing]

Another way of looking at efficiency, Tha I beieve to be an important factor is powder burn rate.

All else equal, a smaller case can better utilize faster burning powders. That's the jist of how the small cases are so efficient.

Also, it has an even much bigger effect to increase bore size, ie neck in up.

A 30br with h4198 and a 110-125gr bullet, vs a 6br with 105-108s and varget is a good example.

I would define efficiency as doing the same or more work in less time, as opposed to another combination

 

[alinwa]

.... The most accurate case is a 270-308 AI so far.

...

Well........ that's only cuz there ain't no 270 Creedmoor yet......

 

[K22]

I don't know if a 22 BR is more accurate than a 22 250 because I never owned a 22 BR. My stock factory Rem 700, 22 250, varminter held groups under 1/4 moa until the barrel went south. Probably the 22 BR holds it's accuracy longer because of the overbore of the 22 250 but my 22 250 was about as accurate as a rifle can get once I found the load for it.*

*While not the best velocity, the most accurate load I found for my 22 250 was IMR 4350 with Nolser 50 BT in a 14" twist. I would never have believed that this powder was suited for the 22 250 until a fellow shooter turned me on to it. Nosler has published load data for it so it's not one of those 'crack pot' loads. Velocity was only about 3500 f/s but it shot consistent sub 1/4 moa groups with this load combo

 

[HTSmith]

Hmmm. Long case.....short neck.....belted head......everything that's not spoze to shoot these days. Yep the 300 Winchester Magnum....Our Military's new sniper cartridge. This stuff confuses me!

 

[Alex Wheeler]

Actually, there was some experimentation some years ago by Fred Hasecuster and a few others. The 6 BR case was shortened by various lengths. The one I had/have is .100 short, making it much closer to the capacity of a PPC. It shoots on a par with a 6 PPC, but is a PIA to make. Since you already have the PPC, there isn't much point, but it did/does work.

Rick

I am not surprised. However if a shorter fatter powder column was inherently more accurate it should shoot smaller than a ppc. Pain or not, if it shot better than the ppc guys would do it. The shorter powder columns do seem to be the best shooters, but I dont know how much of that is short and fat VS the right size/efficient. If you blew out the ppc case to the same volume as a 6br would it shoot worse because the powder column was narrower? I doubt it.

 

[ebb]

I was told it has to do with an efficient case that doesn't use so much powder that it up sets the bullet as it leaves the muzzle. If I were doing a 270WSM I would do a 300x7 WSM and have the huge amount of good 7 mm bullets to use. And not have to hunt for 7 WSM brass.

 

[sparker]

Cartridge efficiency is what can make one cartridge more accurate then another.
When a smaller capacity cartridge, can produce near equal velocities for a given bullet weight, it is more efficient, hence; more inherent accuracy.

Cartridge Efficiency:
(Bullet Weight * .5) * (MV ^ 2) / (Charge * Joules per grain) / 98000 = % of efficiency
Note:: (kJ/kg / 15.4324 = Joules per grain)

Examples:
6Dasher:: 105-VLD <> 3000-fps <> 32.5 of RL-15 = 57.4%
243-Win:: 105-VLD <> 3000-fps <> 44.5 of H4350 = 44.9%

It has been my experience that for distances 600 yards and beyond,
When the bullet/powder weight ratio is right around 3.3 great accuracy happens. .308, .223, 6BRX.

So, with a 30-06, I would predict stellar accuracy with 185 hybrids or similar bullet using around 56 grains of powder

 

[270WinDude]

Looks like I got some more reading to do. Thanks for all the info so far. From my understanding the 270wsm is accurate as it’s common to neck up to 284 for long range competition and the competitor I saw said “everybody” uses it now. . I haven’t heard of the 270-308... I can see efficiency playing a role as a strong variable to accuracy.

 

[Ray B]

Cartridge reviews amuse me when they say a cartridge is "intrinsically accurate" as if there are cartridges that are intrinsically inaccurate. With all the variable that were mentioned kept constant the main thing that will cause one cartridge to be more accurate than another is the shape of the cartridge and its interaction with the rifle that allows for repeatability. A shape that promotes a consistent burn of powder and development of pressure from one cartridge to the next will help the cause of one bullet traveling from case to muzzle in as near as possible the same way- thus potentially traveling the same path to the same spot on the target.

 

[M14AMU]

nice picture, is that a typical 6" mil bullseye?
(pics with no reference are just pic's,
what distance, and how big is the target)

It's standard Palma target dimension! White plate is 20" diameter and it's 15 shots from 1000 yards.

 

[STS]

I have read about the short fat cases being more accurate. But its not like we have a lot of control over the fat part of the equation. If that was the whole story why are we not seeing shortened 6br cases instead of ppcs? You could make a shorter fatter case of equal capacity stating with br brass and I know they played with the br case a lot.

Good point Alex. I know and shot with several guys that worked extensively with the shortened BR case. The so called Tall Dog and .150 short BR. I seem to remember that one of the biggest problems they had was with cases that had the neck made of brass that was formerly in the shoulder of the case. When they pushed the shoulder back and then neck turned they had issues with case growth and donuts. Things might be better now if someone were to try that now that annealing and case forming is more mainstream. Those cartridges shot good but were tough to keep working due to brass problems.

 

[STS]

Cartridge efficiency is what can make one cartridge more accurate then another.
When a smaller capacity cartridge, can produce near equal velocities for a given bullet weight, it is more efficient, hence; more inherent accuracy.

Cartridge Efficiency:
(Bullet Weight * .5) * (MV ^ 2) / (Charge * Joules per grain) / 98000 = % of efficiency
Note:: (kJ/kg / 15.4324 = Joules per grain)

Examples:
6Dasher:: 105-VLD <> 3000-fps <> 32.5 of RL-15 = 57.4%
243-Win:: 105-VLD <> 3000-fps <> 44.5 of H4350 = 44.9%

What we're talking about here is a happy chemical reaction. The happier the reaction the better the potential precision.

 

[msinc]

.......A 6PPC is not accurate due case design, but due to it's combinations and vast use.......

Maybe I am reading it wrong, I don't know...the PPC was extremely accurate enough when Palmisano won his first benchrest comp....and it certainly was not in "vast" use then, wasn't he the only one using it in the beginning??? Isn't small primers and small flash holes filed under "case design"??? Maybe not???? and not the only reason it's an accurate round, but they sure weren't in "vast use" until after the PPC came along.
I wont argue with anyone that there are definitely some cartridges that are inherently more accurate than others.
Maybe I am missing something else here, but I will say that I am not so sure "efficiency" and "accuracy" are married and that you cannot have one without the other or that all accurate cartridges are also efficient ones. First, define accuracy...we all know what that is, something I rarely have. Then, define efficiency as it relates to a given cartridge.....now tell me how they connect.
Don't get me wrong, I will be the first to say that many efficient cartridges are also accurate ones...the 7mm-08 comes to mind right off the bat, but there are also many non-efficient cartridges that even with my limited shooting skills I have shot some great groups with. If they are so connected then how can we explain that????
Let me say it another way...the only "happy reaction" to firing my 8mm Rem mag is when it is over, but I have put three bullets in the same hole at 100 meters with it.

 

[msinc]

Hmmm. Long case.....short neck.....belted head......everything that's not spoze to shoot these days. Yep the 300 Winchester Magnum....Our Military's new sniper cartridge. This stuff confuses me!

Buddy, nothing the federal govt. does should confuse any of us!!!!

 

[retired]

thank you...got to have some reference.
( i know nothing about 270, i told him to go talk to AL)

It's standard Palma target dimension! White plate is 20" diameter and it's 15 shots from 1000 yards.

 

[Grimstod]

I have read about the short fat cases being more accurate. But its not like we have a lot of control over the fat part of the equation. If that was the whole story why are we not seeing shortened 6br cases instead of ppcs? You could make a shorter fatter case of equal capacity stating with br brass and I know they played with the br case a lot.

Just because it's short and fat does not mean it will have a wide load node. Its about having the corect ratio of all three things i mentioned. A gold standard example would he the PPC. Mike Ratigan shortened it further to make the 22-100 and it did not ag as well thought it sometimes made tinny groups. You can get to short and to fat.

 

[Grimstod]

I am not surprised. However if a shorter fatter powder column was inherently more accurate it should shoot smaller than a ppc. Pain or not, if it shot better than the ppc guys would do it. The shorter powder columns do seem to be the best shooters, but I dont know how much of that is short and fat VS the right size/efficient. If you blew out the ppc case to the same volume as a 6br would it shoot worse because the powder column was narrower? I doubt it.

The PPC does not ag as well when you blow out the case to be more near the capacity of the BR. Seen that first hand.

 

[gunsandgunsmithing]

The PPC does not ag as well when you blow out the case to be more near the capacity of the BR. Seen that first hand.

Hmmm. What powder and bullet? I'm seeing a ton of promise from a 6 Grendel with 80's. This barrel has won at least one yardage in every match so far. It sure ain't bad. I have won at 100 with it but it shines at 200 with the better bc and shooting the 80's at the same speed as a lot of people shoot 68's from a ppc. Most short range matches are won and lost at 200.

 

[STS]

Just because it's short and fat does not mean it will have a wide load node. Its about having the corect ratio of all three things i mentioned. A gold standard example would he the PPC. Mike Ratigan shortened it further to make the 22-100 and it did not ag as well thought it sometimes made tinny groups. You can get to short and to fat.

Bill Forrester used the .22 PPC .100 short to set a number of Unlimited Class 10 shot aggregate records. They would agg. well but they were more difficult to keep in tune because of the aforementioned case issues from setting the shoulder back. I had a bunch of them over the years and experienced the trials that made them what they are. Great precision but difficult to live with.