Accurate Loading of Standard Cartridges
1 - Bullet Alignment or runout - Attempt to aim for a 0.002 max bullet runout. It is not unusual for runout to vary from 0.001 to 0.005. It has been suggested that 0.001 inch of runout adds half an inch to a group at 100yds.
2 - Use Fire-forms cases that fit the individual rifle
3 - Choose powder than will totally fill the case
4 - Concentricity Gauge will determine if bullet it aligned
5 - Create a perfectly straight cartridge with zero neck variation
6 - Dies must be of good quality and produce straight cartridges. Using Redding type neck-size die and Wilson chamber type straight line seater will help in controlling accurate bullet runout
7 - Finely neck turn to ensure even thickness around cartridge neck. This will allow an smooth release of the bullet and avoid an uneven release where the neck stretches at the thinnest point.
8 - External Primer Pocket uniforming (possible use of drill). Must be exactly the same depth.
9 - Internal flash hole de-burring - Flash hole must be the same length. Note : Length and not diameter is the crucial flash hole dimension. Adjustable cutters limits the depth of the cut assuming the cases are all cut to the same length. If the cases are not exactly the same length then de-burr with the same number of light turns.
10 - Primer Seating - When using a seating tool then seat with exactly the same pressure. Hardish seating pushing primers past the anvil is usually preferable
308 Winchester Accuracy Loading Tips
Ackley Improved Cartridges
Ackley Improve cartridges form the basics of creating an accurate bullet. The Ackley design comprise of a 40 deg sharp shoulder angle and a non tapered body. Compare this to the shoulder angle (26 deg.) and normal taper of the standard 6mm Remington. The Ackley version has about 9% more capacity, produces less bolt thrust (according to Ackley's theory), and reduces case stretching.
Standard Deviation and Powder Load Tuning
When tuning a rifle there can be up to 3no 'Standard Deviation' peaks where there is a minimum muzzle velocity spread. These minimum muzzle velocity spreads can be found by using a Chronograph.
Best accuracy is usually found just about these 'Standard Deviation' peaks.
With a 6PPC this represents an approx additional powder load of approx 0.3gr (ie - If the lowest muzzle velocity spread is found at 29gr then increase load to approx 29.3gr for maximum accuracy).
PPC Load Tuning Tips – by Gene Beggs
6ppc with a LV contour 22 inches long shooting 68 grain bullets with N133
powder, the tuning nodes or "sweet spots" as some shooters call them, appear at
120 fps intervals. Or, expressed in terms of powder charge, 1.2 grain intervals.
Most benchrest rifles behave in a similar fashion. You can prove this with your
rifle by shooting several three shot groups beginning at 27 grains and
increasing in .3 grain intervals up to a max of 30 grains. If the rifle is in
tune and shooting dots at 27 grains, it will begin to show vertical at 27.3
grains and will be completely out of tune at 27.6 grains. It will come back
together at 28.2 grains and will again be completely out of tune at 28.8, the
last node appearing at 30 grains.
Once the rifle is in tune, make a note of the density altitude and charge weight. If DA increases by 500 feet, decrease the load by .3 grains and vice versa.
If DA goes up decrease the load; if DA decreases increase the load. The formula is .3 grains per 500 feet DA. Since temperature is the main reason for changes in DA you can accomplish the same thing by using only a thermometer. The ratio is .3 grains per five degrees F
On a Culver
type measure, each full number represents .6 grains of the powders we normally
use in the 6PPC, i.e., N133, H322, Benchmark, etc. Make your adjustments in .3
grain increments which is half a number, which in turn equates to 30 fps change
in muzzle velocity.
You must decide whether you will tune with the powder charge or a moveable tuner; you should not try to mix the two. When tuning with a tuner, you never change the load.