07-12-2012, 12:56 AM
I'll start with answering question #2. There is no way to calculate where different loads will impact. This is because the barrel is vibrating as the bullet travels down the barrel and the point of impact, especially at short range is more dependent on the barrel position as the bullet exits than the external ballistics of the bullet.
The m855 load you mentioned is notoriously inaccurate but other loads using quality bullets at moderate velocities will be very close to the Mk262 load which is a very accurate load. For instance I shoot 52grain Sierra Match Kings at 3,200 fps, 77 grain match kings at 2,750 fps, and 80 grain match kings at 2,800 fps and they are all within 1/4 MOA at 100 yards. But that M855 is over 3 MOA different in point of impact. At 600 yards the 77 and 80 grain loads are within 1.5 MOA of one another and the M855 is about three feet lower and the 52 SMK is about 5 feet lower if it even makes it on the target it has to be relatively calm.
My advise would be to choose a load that your rifle shoots well using a bullet that has a reasonable BC and stick with it. Zero it at 100 yards since that is the range you have and then calculate point of impacts at the yard lines you plan to use. JBM is one of the most respected ballistic calculators out there. Just inter the required information starting with the bullet you are using and the muzzle velocity and hit calculate, that will put you within 1 MOA or less out to 1000 yards for normal conditions. If you want to be more precise then you will need to measure your sight height above the center line of your bore, enter your temperature, humidity, and altitude to get you very close.
But nothing beats actually shooting at the actual yard lines. It is all pretty meaningless anyway until you do because you will not understand how to read the conditions to properly dope them.
http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
Bob
The m855 load you mentioned is notoriously inaccurate but other loads using quality bullets at moderate velocities will be very close to the Mk262 load which is a very accurate load. For instance I shoot 52grain Sierra Match Kings at 3,200 fps, 77 grain match kings at 2,750 fps, and 80 grain match kings at 2,800 fps and they are all within 1/4 MOA at 100 yards. But that M855 is over 3 MOA different in point of impact. At 600 yards the 77 and 80 grain loads are within 1.5 MOA of one another and the M855 is about three feet lower and the 52 SMK is about 5 feet lower if it even makes it on the target it has to be relatively calm.
My advise would be to choose a load that your rifle shoots well using a bullet that has a reasonable BC and stick with it. Zero it at 100 yards since that is the range you have and then calculate point of impacts at the yard lines you plan to use. JBM is one of the most respected ballistic calculators out there. Just inter the required information starting with the bullet you are using and the muzzle velocity and hit calculate, that will put you within 1 MOA or less out to 1000 yards for normal conditions. If you want to be more precise then you will need to measure your sight height above the center line of your bore, enter your temperature, humidity, and altitude to get you very close.
But nothing beats actually shooting at the actual yard lines. It is all pretty meaningless anyway until you do because you will not understand how to read the conditions to properly dope them.
http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
Bob