[Rocket J Squirl]

You can generally use the caliber add either +5 or +10 grains. Depending on who you talk to, or use the Davenport Formula, which will tell you the optimum burn rate for you barrel length and bore size.

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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, AND THE WIDTH OF THE LANDS,to work out EXACTLY the cubic area of that particular bore>

Assume you are shooting a 28 inch .50 caliber rifle barrel. T
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 sq. in.
0.197136 x 11.5 = 2.267064 Grains per inch.
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) Groove Depth and Land Height are the same.

Now assume that there are 6 lands and grooves, of equal width. The circumference of that bore( .490) is 1.539384" Divide that by 12( 6 grooves and 6 lands) and you get the width of the lands and grooves to be .128282.

To adjust the cubic area to correct for these "obstructions", you need to subtract the area occupied by those 6 lands, that are .128282" wide, and .0055" deep.

So, multiply 6 times( # of lands) .128282 times .0055(height of lands) = .0042333"

.197136 - .004233 = .192903 Cubic Inches
The cubic area of that .501" bore will be 28 x .19635 = 5.4978 cubic inches. The cubic AREA OF THE ACTUAL BORE, FACTORING IN THE LANDS, WILL BE
5.4012"

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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!)