hill37 Wrote:As I understand it, smaller diameter=longer bullet for the same weight=higher BC. Right?

bj139 Wrote:Is this really worth doing for 0.020" less diameter?

bj139 Wrote:I know but is this difference large enough to have a meaningful improvement in performance?

In my view, it's a whole new ballgame ---

(http://www.65grendel.com/forum/showthread.php?15189-Current-6mm-Grendel-barrel-makers-BHW-McGowen-and-who-else&p=170192&viewfull=1#post170192

Particularly, in view of the all-new CMMG ANVIL action, with their "take no prisoners" POWERBOLT ---

(http://www.65grendel.com/forum/showthread.php?14838-CMMG-6-5-Grendel&p=165540&viewfull=1#post165540)

ETA:


(http://www.rifleshootermag.com/uncategorized/6-5-grendel-evolution/)

Enter: The 6mm Grendel Improved, the obvious next step in the Grendel Evolution --- and, with improved ballistic superiority, further separates us from the 6.8 crowd.

CavityBackBullets Wrote:As a bullet designer that has done a lot of work personally pushing different calibers to their upper limits.
You cannot look at case capacity alone. You also have to look at available pressure.
Available pressure and time under the pressure curve is what makes bullets go faster.
Of course that speaking of internal ballistics and not including rifling profiles, engraving friction and bore lining.

Another thing that is seldom mentioned is the width of the shoulder and how it effects pressure when looking for maximum performance.
This is why Weatherby used the rounded shoulder they did. I am working with a long range bolt rifle company that has went to the Weatherby shoulder in a new cartridge they are designing due to less pressure spiking.
This is also one reason the 30 Herrett can push a 125 grain bullet 2791 FPS from an 18in barrel. Now granted it does not have the high BC you all love, however it does speak to what I am pointing out.

There is a new TAC6 coming out on the 6.8 case.
With the current support by Nosler and Federal on 6.8 case based cats it may be worth looking at.

I do not think pushing the 6mmAR shoulder forward such a small amount will gain what your looking for.

CavityBackBullets Wrote:As a bullet designer that has done a lot of work personally pushing different calibers to their upper limits.
You cannot look at case capacity alone. You also have to look at available pressure.
Available pressure and time under the pressure curve is what makes bullets go faster.
Of course that speaking of internal ballistics and not including rifling profiles, engraving friction and bore lining.

Another thing that is seldom mentioned is the width of the shoulder and how it effects pressure when looking for maximum performance.
This is why Weatherby used the rounded shoulder they did. I am working with a long range bolt rifle company that has went to the Weatherby shoulder in a new cartridge they are designing due to less pressure spiking.
This is also one reason the 30 Herrett can push a 125 grain bullet 2791 FPS from an 18in barrel. Now granted it does not have the high BC you all love, however it does speak to what I am pointing out.

There is a new TAC6 coming out on the 6.8 case.
With the current support by Nosler and Federal on 6.8 case based cats it may be worth looking at.

I do not think pushing the 6mmAR shoulder forward such a small amount will gain what your looking for.

m796rider Wrote:What about terminal ballistics? I see 6mm projectiles dominate PRS and other LR competitions, but are they useful for hunting medium sized game?

One of the nice things about Grendel is the immense body of data around the effectiveness of 6.5mm projectiles in harvesting game.

K_4c Wrote:6mm's have been harvesting medium sized game for years. Also allows for lighter loads for thin skinned animals. Light recoil, flat trajectory, etc... barrel life is its only major draw back. But if you're burning out barrels, cost of ammo exceeded the barrel and smith work roughly by 2x -3x's.

bj139 Wrote:If you are punching paper at long range this looks to be a good idea but for game animals I don't know.

Larger 6mms (243win, 6mm rem) have higher velocity to compensate for the lighter bullet. . .

From my personal experience, I have taken Colorado Mule Deer with one-shot kills using a Remington Model 660 Carbine (20" barrel) chambered for the 6mm Remington, using Remington factory-loaded 6mm Remington Hi-Speed 100-grain Pointed Soft Point CoreLokt ammunition. Compare the downrange velocity and energy values of the 6mm AR Turbo 40 Improved, with the Sierra 110-grain HPBT Matchking projectile (BC - 0.617) (A) and the factory-loaded 6mm Remington, with the Remington 100-grain Pointed Soft Point CoreLokt projectile (BC - 0.356) (B) out to 1,000 yards, with a 10 mph crosswind, from 24" barrels:

LRRPF52 Wrote:More case capacity with the optimum powder density and burn rate will result in higher mv.

The shorter, fatter powder column in a Grendel or BR-type case will burn more efficiently than an early 1900's type 30 Remington-based case.

It's one of the reasons you see 6.5 Grendel at lower working pressure getting the same speeds as a 6.8 case with the same bullet weight pushed to higher pressures.

It makes no sense at all to use a lower capacity case with inferior shaping to it when we're trying to get more mv, especially with the lower bore volume of a 6mm.