Guess you guys have not heard of the Davenport formula.
Its will give you the optimum load for your barrel. Not the most accurate.
What it will tell you is if you are wasting powder.
In my 45 cal I used to use 55gr 3f (1600fps) for all my targets below 100 yards, then Id double the charge (110gr 2000fps)
for 100-150 shots.
After running my barrel measurements through the formula, I found that 75gr got me 2000fps, and everything else was wasted.
So now I have a custom made powder measure that has a mark for 55gr, and filled is 75grs.
Below is a copy of an e-mail I save for giving out the formula, its not as hard as it looks.
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The Cubic area of the bore would be done this way:
Take the bore diameter( or groove diameter and then calculate both cubic areas. Then subtract the area created by the lands, to get the actual true Cubic area of a rifled barrel. Generally, the difference is measured in a couple of grains, and is not worth the extra brain power used.) and divide it by 2 to get the Radius of the bore. (r)
Area of a circle is determined by the formula A= PiR Squared. Pi= 3.1416. So, Multiply the Radius by itself(to square it) and then multiply that number by Pi to find the area of the circle the diameter of the Bore of your gun.
Now Multiply that number( area) times the 11.5 to get the amount of powder in one inch of your bore. Multiply that number by the length of your barrel to get the total capacity for your whole barrel.
Example:
( .50 cal. divided by 2 = .25; times .25 = .0625; times 3.1416= .19635; times 11.5 =2.2580; times 28(barrel length)=63.22 grains of powder.)
If you want to know the cubic space inside one inch of a .50 caliber rifle, you can use .50 as the diameter, or measure the actual land to land dimension, and then the groove diameter, and then the groove depth, to work out EXACT the cubic area of that particular bore.
Here is how to calculate the Davenport Formula:
.50 divided by 2 = .25
.25 x .25 = .0625
.0625 times Pi( 3.1416)= 0.19635
.19635 x 11.5 = 2.2580
2.2580 x 28 inches( barrel length)= 63.22 grains of powder.
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Assume you are shooting a 28 inch .50 caliber rifle barrel. The cubic area of that bore will be 28 x .19635 = 5.4978 cubic inches.
Now, because you do have grooves in that barrel, you can refine that a bit more.
Assume that the actual groove diameter of your gun is .501" ( my .50 caliber rifle's actual bore diameter)
Run the Davenport formula and you get:
.501 divided by 2 = .2505
.2505 x .2505 = .0627502
.0627502 x 3.1416 = 0.197136
0.197136 x 11.5 = 2.267064
2.267064 x 28 = 63.477792 grains of powder.
A cube of anything is determined by multiply the height times the width, times the depth, of the object. When you need to compute the cubic area of a cylinder, or other non-square object, it gets a bit more involved.
Now assume that the bore diameter is actually .490, and groove depth is .0055"( .501 minus .490 divided by 2 = .0055")( again, my gun's actual bore diameter)
Now assume that there are 6 lands and grooves, of equal width. The circumference of that bore( .490) is .769692" Divide that by 12( 6 grooves and 6 lands) and you get the width of the lands and grooves to be .064141".
To adjust the cubic area to correct for these "obstructions", you need to subtract from 5.519808 the area occupied by those 6 lands, that are .064141" wide, and .0055" deep.
So, multiply 6 time times .064141 times .0055 = .0003527"
5.519808 - .0003527 = 5.5194553 Cubic Inches
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If we ran the davenport formula using the Land to land diameter( bore diameter) of .490, we get:
.490 divided by 2 - ..245
.245 x .245 = .060025
.060025 x 3.1416 =.1885745 square inches. ( for a circle that is .490 in diameter.)
.1885745 x 11.5 = 2.1686067 grains per inch
2.168067 x 28 = 60.720987 grains of powder.
So, if you use the smaller diameter of the bore( land to land[.490]) The Davenport formula will give you only
60.72 grains of powder in that 28 inch barrel.
If you use the nominal .50 caliber, the formula gives you
63.22 grains of powder in that 28 inch barrel.
And, if you do all the math needed to actually get the ACTUAL cubic area of that barrel, you get a figure in between those two, 60.7, vs. 63.2! That is a difference of 2.5 grains, and half( assume that the lands and grooves are of equal width) that is only 1.25 grains!( Approx. 61.95 Grains!) Not enough to bother about, NO?