Loading by density Part 2) Playing with the numbers

My Savage Model 14 270WSM has a BFTL dimension of 2.3265. The cases from and for this camber have been neck turned to a wall thickness of .015 and trimmed to a length of 2.0855. The case base to neck bottom is 1.824 and case base to shoulder is 1.6642. Subtracting the base to neck dimension from the trim length gives me a neck length of 0.2615. As another rule of thumb you’d like your neck length to be equal to the caliber diameter. In this particular case this isn’t the case, but not that big of a deal. My “dry” case w/primer is 239.90 grains; “wet” weight is 319.86. This gave me a full case weight of 79.96 grains. The bullet that I’m using is Hornady SST 130 grain. In a bit I’ll explain how I measure all aspects of the projectile.

Constants & Formulas:

1) A cubic inch is equal to 16.387 cubic centimeters (cc)

2) A cc is equal in weight to 1 Gram (G)

3) A gram weighs 15.42 grains (gr)

4) A cc of water weighs .9971

5) Caliber radius formula is; caliber / 2 = caliber radius

6) Caliber radius squared formula is; caliber radius X caliber radius

7) The formula for volume of a cylinder is; height X PI(π or 3.14) X caliber radius squared

Bullet Dimensions (not weight) that need to be determined:

1) Overall Length; tip of nose to base

2) Base to Ogive; distance from base to caliber diameter of nose

3) Tail Length; distance from base to the caliber radius of tail

4) Length of Nose; distance from caliber diameter of body to tip of nose

5) Bearing surface; the length of the bullet that has a caliber diameter

Measuring the Bullet:

Step 1) with your calipers measure and record the overall length.

Step 2; add one comparator to your calipers and zero, put the nose into the comparator, measure and record the base to ogive dimension.

Step 3; turn the bullet around putting the tail into the comparator, measure and record the tail to ogive dimension.

Step 4; add another comparator to the other jaw of the calipers and re-zero, then measure and record the tail ogive to nose ogive to determine the bearing surface.

Subtract base to ogive (Step 2 above) dimension from the overall length (Step 1 above) dimension, the difference equals the nose length of the bullet. This dimension will also be used to compute seating depth in a moment.

After you have measured different bullets by different manufacturers you’ll see a significant variance between nose lengths compared to ogive. This is due to each manufacturer using a slightly different secant formula when designing their bullets. OK, time for another example.

Comparing Nosler’s 130gr Ballistic Tip to Hornady’s 130gr SST here’s what I found in the lots I measured:

1) Overall length: Nosler 1.2260, Hornady 1.2455

2) Bearing surface: Nosler .6095, Hornady .5060

3) Nose Length: Nosler .5405, Hornady .6015

4) Base to Nose Ogive: Nosler .6805, Hornady .6440

5) Tail Ogive: Nosler .0760, Hornady .0980

Conclusions based on the dimensions in the above comparison. The nose of the Hornady’s is longer and thus a larger secant multiplier was used to determine the profile. Nosler utilized a shorter tail length and smaller secant multiplier to accomplish a longer bearing surface. The shorter base to nose ogive on the Hornady will result in a shallower seating depth to reach the desired CBTO less jump dimension for the cartridge. A shallower seating depth as means there’s more capacity for powder.

How about a break?

And NOW a brief message from the cases and variants thereof by manufacturers.

YUP! Gotcha!

NO BREAK HERE!!! Continuing on…

Every case manufacturer uses a slightly different alloy formula. They are all protected by patents you know. All have to have a different alloy content to keep the court system from being overloaded. Dang ATTORNEYS!! (Sorry Bill) The variance in alloys has an effect on weight, wall thicknesses and stretch factor and work hardening properties. This is also why each case will have a slightly different volume capacity. Take for instance my 270WSM cases, a Federal R-P weighs 234.10 grains and has a capacity of 80.72 grains, while a Winchester has a weight of 235.00 and a capacity of 79.96. Mind you both of these cases were trimmed to the exact same length of 2.0855. Both were also neck turned to a uniform thickness of .015. Now this seems to be a real chin-scratcher

for sure. But the only possible explanation is wall thickness. Oh by the way.

Another of my little tricks, on all my magnum rounds I drill the flashole to a diameter of .090. The uniform flashole diameter from the factories is .082. Why do I do this? I dun-no

just always have.

We’ve FINALLY gotten to the meat and potatoes of this whole thing! Loading by density!

As I showed in the example of my Savage Model 14 270WSM. I used Winchester cases in this example. Remember my primed case dry weight was 239.9 grains. The wet weight was 319.96 grains. This gave me a full case volume capacity of 79.96 grains of water. Next I have to determine how much of this capacity is going to be taken up by the seated bullet. Using bolt face to land dimension of 2.3265. I want a jump space of .005, so I subtract .005 equaling 2.3215. To determine seated bullet volume I add the case trim length of 2.0855 and the bullet base to ogive dimension of .6440. These two measurements total 2.7295 and is my cartridge base to ogive length. I now subtract the jump dimension; 2.7295 - .0050 = 2.7245. The equation to find the seating depth would be; 2.7245 - 2.3215 = .4030 of an inch.

Remember the volume of a cylinder the formula? Here is where you’re gonna need it. It was #6 from constants and formula section above. The caliber radius of the .277 is .1385 so the caliber radius squared is .0192. Here is the equation to find the volume displaced by the seated bullet. 4030 X 3.14 X.0192 = .0243 cubic inch. To convert this to cubic centimeter multiply the cubic inch number by 16.3871 which is how many cc’s are in a cubic inch. This equation is; .0243 X 16.3871 = .3982 cubic centimeter. Remember 1 cubic centimeter is equal to 1 gram. So the gram weight is also .3982. There are 15.324 grains in a gram. The grains displaced by the seated bullet formula is; .3982 X 15.324 = 6.14 grains. Then subtract the displaced volume of the bullet 6.14 from the 79.96 volume of the full “wet” case to find the net capacity, in this case it is 73.82 grains. The last step before using this to compute charge weights is to have the gram weight of the net capacity. To determine this divide 73.82 by 15.432 and we come up with 4.7837 in this instance.

Don’t know ‘bout y’all but I need a cup of coffee and a brain break. In part 3, I’ll show you how to use Powder Density Factors in figuring charge weights. Yeah a whole lot more math. But I’ve got a surprise! For the last 18 months I’ve been working on an excel spreadsheet to do the cyferin’ for ya. Talked to Brother Bo (the excel guru) and he’s going to proof it for me and more than likely help me finish it up.

PRACTICE! PRACTICE! PRACTICE! PRACTICE! Then practice a little more! Dutch OUT!

I can attache a PDF if anyone is interested.

A little bonus reading for your pleasure.

Rules of the Reloading Road

Rule 1 - Don't do anything stupid.

Rule 2 - For a given load a 3 percent rise in velocity requires a 6 percent rise in chamber pressure.

Rule 3 - For a 3 percent change in case capacity chamber pressure changes by 6 percent. Remember that case capacity varies drastically between brands of cases and that bullet seating depth also changes case capacity.

Rule 4 - Changing ANY component can drastically affect chamber pressure.

Rule 5 - You DO NOT need to wring the last possible foot-second of velocity out of your ammunition--it won't do anything for you. An accurate/moderate velocity load is better than an inaccurate/fast load.

Rule 6 - Temperature affects chamber pressure. While the effect differs with each powder, over the range of about 0º F to 125º F most modern commercial powders are fairly stable showing pressure variation of up to ± 3000 psi from loads developed at 70º F.

Rule 7 - Altitude change will alter the static pressure inside a loaded case. Cases loaded at a low altitude will have an internal pressure rise at higher elevations. This starts to occur around 4500 feet of change but doesn’t become critical until greater than 8000 foot change. If loaded at high elevations the reverse is true when they are brought to lower an elevation.

Rule 8 – REPEAT RULE 1!!! Don't do anything stupid!!!