The most accurate cartridges tend to be those with not much body taper and about a 1:2 to 1:3 ratio of powder charge shape/container diameter to length. Measure the case diameter 2/10ths inch in front of the case head and the distance from that point to the case body-shoulder juncture. On the .308 Win. case, they're .470":1.36" giving a 1:3.32 ratio; about the upper limit. But sub caliber cartridges based on the .308 case have shot very accurate. Cartridges with a smaller ratio, such as the PPC cases and 6.5x.284 cases have smaller ones. The 6mm Dasher's ratio is 1:2.13. Greater ratios like the .30-06 case and its sub caliber offspring, have a 1:3.72 ratio and they're not popular in long range accuracy rigs. Shorter, fatter powder charge shapes are easier to more uniformly ignite and burn. The pressure curves they cause produces more uniform peak pressures and muzzle velocities as well as barrel times to bullet exit.
Another thing common to accurate cartridges is shoulder angles being on the larger side as well as shoulder area. The more of both there is for a given cartridge, the less the shoulder sets back from firing pin impact. That makes the primer detonate more uniformly which means so will the powder charge. The 17.5 degree shoulder angle of the .30-06 case let it set back as much as .005" to .007" from firing pin impact. Compared to the .308 Win case 20 degree angle and larger shoulder area by its larger shoulder area limits its shoulder setback to .002" to .003" when the primer detonates. 24 caliber cartridges with 30 and 40 degree shoulder angles and a lot more shoulder area withstand firing pin impact very well and set back only .001" or so; very uniform primer ignition. The 6mm Dasher's 40 degree shoulder angle coupled with its charge ratio is impressive.
Note the link above on the 6mm Dasher's new record is the smallest aggregate ever shot; it kept all shots inside 7 inches but where the 10-shot group centers were relative to the aiming point is unknown. All the other agg's are larger; much larger. That rifle was fired in free recoil untouched by its owner except for a finger on its few-ounce trigger. Neck sizing afficianado's should note full length bushing dies were used on cases with 100 or so reloads with them.
