I get really confused about “inherently accurate” and other gun store statements about accuracy.
First we need to define what causes accuracy. To me, this is really tough, but I start with short range accuracy. For a modern rifle, I define that as 100 groups, specifically 5 shot groups shot off a benchrest by a perfect shooter. This allows wind and drop to be ignored. Let’s ignore the rifle factors for this post. So, what factors of the cartridge. IMO, those main factors are bullet alignment to throat, consistent bullet release point, bullet fit to bore....
From a mathematical point of view, we are aligning a cylinder within a cylinder. Using the concentric cylinder model, with a standard radial gap, the longer the round, the less misalignment is possible. Hmmm.
In addition, with axial force like the push feed ejector, the more case taper(shoulder and body) the better.....so something like 30’06 should be best.
Looking at government designs, they seem to buy into this...223, 30’06, 50 bmg.
So this gets the case lined up....what about bullet to case alignment? Seems like I want a case that has good neck to bullet engagement. Again thinking about concentric cylinders. I’m not sure what is best, but when I look at 222 Rem, 6 ppc, 6 Dasher, 6.5 creedmoor, they all have neck length to diameter ratios .98-1.4. While 223 Rem which is generally not as easy to get accuracy from is 0.9.
Then there are the “consistency of bullet release point” factors. This has a lot to do with consistency of burn, case fill, bullet fit to bore, recoil stroke, etc. Really, case fill, land erosion and oal consistency are key here. First land erosion....it has been roughly determined that steeper necks reduce throat erosion with powders that have that issue. So, let’s assume 35-40 degree shoulders are best. Over 40 becomes really hard to form and resize consistently. Case fill.....all I can say is some cases when matched up to available powders, tend to have fill percentages from like 85-95%, 95-105%, and even 105-115%....I believe rounds in the middle to high range are best. High is ok because most rifles require you run rounds long to get anywhere near the lands.
So, what does this tell me.....a round with a long case body, 35-40 deg neck, neck length to bullet dia ratio of ~1.1 and case fill of 105% is best....in addition, it needs to have a variety of accurate bullets/brass available...
So, 222 Rem, 6x47, 6mm creedmoor, 6.5x47, 6.5 creedmoor, 6.5x55, 280ai, 300 Norma....I’m sure there are more.