OK, here we have the promised sample problem:
Lets say we have a gun that weighs 6.44# (6# 7 oz), and has a MOI at CG of 1.50. The shooter checks for point of rotation while unmounted and finds that his hand placement causes the actual rotation point to be 1.20" from the CG. The formula then becomes ((6.44/3.22) X 1.2/12) X (1.2/12)) + 1.50 = (2 X 0.1 X 0.1) + 1.5 = (2 X 0.01) + 1.5 = 0.02 + 1.50 = 1.52. 0.02 is about a tenth of the amount of change in MOI to noticed by most shooters. Keeping in mind that doubling the distance causes a four fold increase in the change in MOI, 0.6" would be 1.505 and 2.4" would be 1.58. Around three inches would cause a noticable change for a gun of the stated weight. Heavier guns would require less change for a noticable MOI increase.
Same gun as above and having 4" balance in front of the front trigger and a 14" LOP. Mounted MOI is found as follows: (((6.44/3.22) X ((4" + 14")/12) X ((4" + 14") / 12)) + 1.50 = ((2 X ((18/12) X (18/12)) + 1.50 = (2 X 1.5 X 1.5) + 1.5 = (2 X 2.25) + 1.5 = 4.50 + 1.50 = 6.00 = MOI at butt.
I forgot to mention that balance tells the proportion of weight carried by each hand. A hand centered under the CG would carry 100% of the gun's weight. If the hands are spread equally from the CG each hand carries 50% of the weight. If the center of the trigger hand was three inches behind the trigger (4" CG to trigger + 3" behind trigger = 7") and the front hand was 14" in front of the CG, the front hand would carry 7/21 + 1/3 of the weight and the back hand would carry 14/21 = 2/3 of the weight. Some shooters are quite sensitive to the proportion of weight in each hand.
Do check my cipherin', I have recently mad some misteakz.
Questions?
Dig, it is possible to fire a gun twice by pulling the single trigger twice. It is not necessarily so, but sometimes.
DDA
Last edited by Rocketman; 05/01/13 01:40 PM.
