|
Post by kbrezlin on Sept 20, 2015 8:20:32 GMT -5
This may sound dumb. Not a target shooter, and have mostly bowhunted for the last 15 years but I'm getting more into the MZ and long range stuff.
does your BC increase as you push the speed up or is it negligible in real hunting world application, say out to 400 yards?
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Sept 20, 2015 19:17:13 GMT -5
in most bc calculation iv'e seen... velocity isn't a variable...what bc a bullet is ,is what it is, is what Im seeing...
|
|
|
Post by Richard on Sept 20, 2015 19:40:32 GMT -5
BC will vary somewhat with the speed. The numbers posted in loading manuals only give a BC based on the form factor. True BC is obtained by checking the velocity at two different points. Based on how much the bullet speed slows down at the furthest point. I have a friend and engineer in Louisiana who sets his two Oehler ballistic chronographs up at the muzzle and at his furthest shooting point with is 280 yards His photo cells at each location are spaced 24' apart (he has permanent poles in place for precise mounting) This set up is capable of getting velocity readings within 1-2 fps. With this set up he can calculate True BC. I asked him one time to give me the BC on one of my custom VLD 6.5 bullets? He said if I gave him certain dimensions (base of boat tail to main diameter, distance of tip to start of ojive, length of the bearing surface), weighted the core, give the distance from the core to the tip that he could give a relatively close BC but it would not be 100% without firing. And the faster you push it the BC will somewhat increase. I take him at his word on this stuff based on his experience and intelligence. So in affect, what you are getting from the bullet manufactures is a "ballpark" figure and usually on the high side.
|
|
|
Post by herman on Sept 21, 2015 8:25:57 GMT -5
If you have a sierra manual,it has a whole section on BC.I stumbled across this one day. With some bullets the BC goes up with speed and some go down with speed if I am reading it right. If I am shooting bench rest long distance I want a bullet with a high BC.But for hunting say out to 300 yds it don't matter what the BC is.If you set your scope for the distances you want to hit.it will be there.But you have to consider the wind also.
|
|
|
Post by kbrezlin on Sept 21, 2015 16:04:46 GMT -5
Thanks for the info. With these big diameter bullets I am convinced the wind drift is probably more of a variable than the drop. Whatever the computer tells me will be verified on the range out to 300 yards. That is the furthest range I can get to.
|
|
|
Post by 247deer on Sept 21, 2015 16:44:13 GMT -5
Thanks for the info. With these big diameter bullets I am convinced the wind drift is probably more of a variable than the drop. Whatever the computer tells me will be verified on the range out to 300 yards. That is the furthest range I can get to. iI think you will find that these big bullets do not drift as bad as you think at three hundred I don't see much drift just my experience
|
|
|
Post by Richard on Sept 21, 2015 19:04:57 GMT -5
Size of the bullet has little to do with it? Its the BC that controls that.
|
|
|
Post by bestill458 on Sept 21, 2015 19:22:45 GMT -5
Help me understand a 270 emax has a b.c. of .384 listed by parker at 2800 fps. I shoot them at verified velocity2450fps muzzle velocity and it takes me 17.5 moa to be on at 500 yds. If i run ballistic chart its no where close to that unless i reduce b.c. by same percentage im reduced from2800 fps. Thanks
|
|
|
Post by keith on Sept 22, 2015 19:02:49 GMT -5
Help me understand a 270 emax has a b.c. of .384 listed by parker at 2800 fps. I shoot them at verified velocity2450fps muzzle velocity and it takes me 17.5 moa to be on at 500 yds. If i run ballistic chart its no where close to that unless i reduce b.c. by same percentage im reduced from2800 fps. Thanks couple of possibilities : 1. If your MV is correct then Parker's BC is wrong if all your other inputs are correct. Doesn't shock me given most calculate BCs instead of testing them. Your BC usually only varies by .01-.017ish per 500fps until you approach transonic. 2. You need to verify your turrets dial what you think they dial. 3. Your twist is marginal and causing an accelerated decay of BC.
|
|
|
Post by bestill458 on Sept 22, 2015 19:14:20 GMT -5
The elevation correction i use is consistent with 3 guns (2) 1-20 twist(1) 1-18 twist 3 scopes vortex,Bushnell,weaver. All chronograph within25 fps avg. If i use.330 b.c. drops work instead of advertised b.c.
|
|
|
Post by keith on Sept 22, 2015 19:21:19 GMT -5
As much and as well as you shoot, and add much as we've talked about twists issues, I would say that if 3 guns with 3 different optics shoot the same data then the BC is not as advertised.
|
|
|
Post by Richard on Sept 22, 2015 20:03:31 GMT -5
It is just "Ball Park!" and inflated at that. It is easy to crank up the speed when testing, above what is normally considered safe, and get a high BC, then publish it as being true?.........This way they do not have to lie, just leave out some of the criteria.
|
|