Extreme accuracy: Bore to capacity relationship?

[wilkup]

I was chatting with another member about this the other night and figured I'd throw this out there in hopes someone may be able to provide some kind of intelligent explanation for this phenomenon.

Somehow the 28 Nosler is easily capable of extreme accuracy with little to no load work up while it's sister cartridge, the 26 Nosler, does not suffer the same benefits.

Does anyone know why/how this happens? I'm wondering if there's some formula available to quantify how accurate a cartridge design is going to be prior to actually sending rounds down range.
Why is the 28 so much more superior to the other calibers within this family? Is it just luck or is there a scientific explanation we can utilize for new rounds?

 

[tbrice23]

I'm not sure if there is a direct correlation.

In my experience an of my 300 WM have been as easy to load for as either of my 308 winchesters.

I've had a 338 WM that was a monster nightmare to load for but both my 7mags have been easy to tune.

I'm pretty convinced it has more to do with the build quality and concentricity and barrel integrity than cartridge design.

 

[toddc]

Anything extremely overbore is going to be harder to load for IMHO.
Pressures are going to spike more and its just going to be more difficult to tune.
Same thing in engines.
I'm not smart enough to detail the science behind it but everything becomes more pronounced at the ragged edge. Whether its guns, motor or roller skates.

 

[Michael Eichele]

My opinion is 1:3 ratio is a good balance. 50 grains of powder and 150 grains of bullet such as the 308. 60 grains and 180 grains for the 30-06. 71-72 grains powder and 215 grains for the 300 WM. 250 grains of powder and 750 grains of bullet for the 50 BMG. All of these loads are easy to tune. It's not scientific or necessarily even worth arguing over but it seems like an approximate 1:3 ratio holds a good pattern even is it's slightly tilted one way or the other. That said, I've had plenty success pushing 180 grains of bullets with 90-100 grains of powder. The barrel (among other things) will help decide how accurate a rifle will be.

 

[MudRunner2005]

I was chatting with another member about this the other night and figured I'd throw this out there in hopes someone may be able to provide some kind of intelligent explanation for this phenomenon.

Somehow the 28 Nosler is easily capable of extreme accuracy with little to no load work up while it's sister cartridge, the 26 Nosler, does not suffer the same benefits.

Does anyone know why/how this happens? I'm wondering if there's some formula available to quantify how accurate a cartridge design is going to be prior to actually sending rounds down range.
Why is the 28 so much more superior to the other calibers within this family? Is it just luck or is there a scientific explanation we can utilize for new rounds?

Any cartridge can be capable of accuracy. But sometimes a cartridge is so overbore that it becomes very finicky and picky. Also, there is a such thing as being overbore (large magnums with 7mm or larger bore diameters), and massively overbore (.26 Nosler 6.5x300 Wby, etc...), and have too many diminishing returns.

 

[wilkup]

If being overbore equates to less accuracy, how would someone describe the accuracy potential of the 30-378 Weatherby? If overbore was going to create a problem in accuracy, this should be a prime example but it's exactly the opposite; this round is highly accurate.
I'm not trying to argue and still interested to learn, it figured I'd throw that out there after a few overbore comments were included.

 

[MudRunner2005]

If being overbore equates to less accuracy, how would someone describe the accuracy potential of the 30-378 Weatherby? If overbore was going to create a problem in accuracy, this should be a prime example but it's exactly the opposite; this round is highly accurate.
I'm not trying to argue and still interested to learn, it figured I'd throw that out there after a few overbore comments were included.

Like I stated, any cartridge can be accurate. Rifle build quality, loading skills, and component quality have a lot to do with accuracy as well.

Like thrice, I also once had a .338 WinMag that wouldn't shoot the broad-side of a barn. I rebarreled it to 7mm ReMag, and problem solved. Which the action later got used for my .300 Ackley build, and the barrel went on my burned-out A-Bolt II.

 

[toddc]

If being overbore equates to less accuracy, how would someone describe the accuracy potential of the 30-378 Weatherby? If overbore was going to create a problem in accuracy, this should be a prime example but it's exactly the opposite; this round is highly accurate.
I'm not trying to argue and still interested to learn, it figured I'd throw that out there after a few overbore comments were included.

I didn't look it up in the overbore guide but that setup isn't as twitchy as a 7RUM or 6.5-300 IMHO. I think there is also a relation to bore size and powder kernel size. A 30-378 will still be twitchier than a 308. Accuracy can be there just harder to find. I have gotten great accuracy with some really overbore stuff it just seems harder to find a load for and if that is the case, then the throat is half smoked before it starts shooting.

 

[Greyfox]

It seems to me that many the most accurate Benchrest rounds like the 22PPC, 6mmBR, 6.5x47, 6.5x284 etc. are overbore. This would fly in the face of the notions about bore to capacity effecting accuracy, and/or difficulty in developing accurate loads. The theory I have heard for the short fat case relationship in overbore cartridges is that the burn is more uniform with less case wall effects. It appears to be proven out with the BR crowd. Just some thoughts.

 

[cacsrx1]

My box stock 6.5-300 Wby shoots 140g Vlds and 143g Eld-x's into .3moa. It was very easy to find an accurate load.

 

[wilkup]

I was really hoping there was some formula to test out accuracy. I'm still there could be but it sounds like it's unknown at this point.
In response to the 6.5-300 in the .3s... i find it interesting the 26 is tough to load accurately and easily but the 6.5-300 you have is not. There's gotta be something different going on there.

 

[cacsrx1]

It absolutely hated factory 127g ttsx's.

 

[toddc]

It seems to me that many the most accurate Benchrest rounds like the 22PPC, 6mmBR, 6.5x47, 6.5x284 etc. are overbore. This would fly in the face of the notions about bore to capacity effecting accuracy, and/or difficulty in developing accurate loads. The theory I have heard for the short fat case relationship in overbore cartridges is that the burn is more uniform with less case wall effects. It appears to be proven out with the BR crowd. Just some thoughts.

There's overbore and then there is OVERBORE. All of the stuff you listed is short fat. Noslers, 6.5-300 and RUM are LONG and FAT. I would guess there is a difference there. I used to know the theort behing the design of the PPC and other accuracy cartridges and its a crazy amount of theory, I've just forgotten most of it.

 

[toddc]

My box stock 6.5-300 Wby shoots 140g Vlds and 143g Eld-x's into .3moa. It was very easy to find an accurate load.

Doesn't mean 1000 other shooters won't have issues with it. One other thought is that a lot of extremely overbore stuff is built on higher quality platforms. This alone skews the results.