Michael Eichele
Well-Known Member
You hit the nail dead on the head. Except you DO NOT want to enter the wheather AND your altitude into the computer together. If you are reading raw pressure at your shooting location the altidute should ALWAYS be entered as 0 feet. If you cannot measure the pressure, then you enter the default pressure and then altitude. Bear in mind if there is higher than normal system or lower than normal pressure system in your area, it can throw off your tests quite a bit. It is always best to measure the temp, local barometric pressure and if possible humidity (if not possible it isnt a big deals as humidity has very little effect on the bullet's flight) and ignore the altitude altogether.
Not exactly.
Bullet's BC's change with a number of factors. The 2 biggest factors that have the most influence on BC would be velocity and stability factor. The 2 biggest factors for stability factor is made up of velocity and twist and bullet demensions. For example, a bullet that is spun much faster than it needs to be will point it's tip more to the right (for a right hand twist) than normal. This will cause more drag on the bullet. Also an overspun bullet will tend to keep it's nose pointed towards the angle in which it was fired (up) even during the length of it's flight. This too causes excessive drag. Overspinning a bullet causes a decrease in BC potential due to these factors. This is a high stability factor. A bullet that is stable yet is riding the edge of under stable will exibit yaw during the first several hundred plus yards before it stabilizes. Because the bullet isn't flying smooth it also restricts BC potential. This is a low stability factor. The better you match your bullets to your twist and velocity, the better your BC will be regardless of bullet type. Now if you use bullets that tend to deliver high BC's due to form and match the twist to it, you will have at least an an advertised BC and in most cases a much higher BC than advertised. Velocity will also have a huge effect on the BC. A quick look at the Sierra loading manual and you will find that they give you different BC's for a given bullet between certain velocities.
So in answer to your question. No. The ACCUBOND 180 will not have the exact same BC from rifle to rifle let alone cartridge to cartridge. Different twists, different velocities, different quaility of land impressions will all come into play. You may find that in most circumstances that the published .507 will be very close from gun to gun and cartridge to cartridge (+/- a small percentage) but there will always be an odd duck that where the stars align just right and it may yield an unussually high BC or the opposite can occur and you will be very dissapointed in the BC you are getting.
I hope that helps.
PS yes most manufacturers use the G1 model. The G models are just different models for different amounts of BC decay. The BC will change during flight. How much it changes depends on a great number of things. If you can not seem to make your ballistic software match your real world tests by manipulating the BC alone, it is time to change the drag model (G model) In alot of cases changing the drag model can help you more closley match your computer to your real world tests.
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