Ballistics

[Cruizin]

Anyone have experience with the polygonal barrels? I just ordered a Rock Creek barrel that has the polygonal rifling. The bullet should be less deformed as it travels through the air. They also say the muzzle velocity is higher than standard barrels.

My question is do I need to take any of this into account when running the numbers in a ballistics program like xbal for example?

 

[Cruizin]

Also I'm curious on how you guys figure out the ballistic coefficient for these wildcat bullets. Since the manufacture doesn't list them.

 

[Black Diamond 408]

To figure BC of a bullet you have to shoot the rifle at known distances, record the drop at each distance, lets say your sighted in at 100yds, then shoot 200, then 400, then 600 and so on to 1000yds. Compare the programs drop for each distance, adjust the BC for the bullet(through the program) until it matches the drop you recorded. This will be the actual BC for the distances your shooting. I used the 300MK sierra in my 338 Snipe-Tac rifle, .768 is what Sierra states, Through my testing and recorded drops my Exbal program came up with a BC of .813 (3325fps) this was shot at an altitude of 1200ft. Its a time consuming process, but can be well worth it to fine tune your program.

I forgot to mention you also need to chrono the loads at each distance to match up the speeds. This can be scary for some, boom goes the chrono!

 

[Cruizin]

Yeah from the research I have done your bullet has a different ballistic coefficient at different distances. So in exbal you just adjust the main bc number until it matches the point of impact and velocity then you just stick with that number right? Or do you have to enter a ballistic coefficient for all the different ranges?