Well how many of you think ballistic programs are accurate? Here is an example of what happened at the range today.

300 win mag 200 gr accubond
Scope height 2 inches
Chrony master with printer at 12 feet
3 strings of five averaging 2851 fps

Balistic program load from disk, JBM, and Chrony

balistic programs say 3.5 inches high at 100 yds and I wwould be aprox 1/2 inch low at 300yds.

Imangine my surprise when I go directly to the 300 yrd range and sight it in for 300 yrd, I mean exactly. Then I go back to 100 yrd to see how high I am there. I was 6 inches high. Yet according to 2 different chronys I am shooting around 2850fps.

I think i must be totaly retarded by I cant figure it out. I know my velocity is there as I am definatly aproching max and it is a 26" barrell. Any thoughts on this would be great.

I'm far from being an expert here, but two things that come to mind are ambient air conditions (temp & humidity), and sight height. The height of your scope in relation to the rifle's bore makes a difference insofar as where the ballistics programs say the bullet should be at a given distance. Temperature and humidity affect air density, which will dictate how well the bullet will rise.

Another thought that comes to mind after posting this is, why not try zeroing it in at a closer distance? That would give you a more consistent rise and fall at the ranges you mention. Six inches difference doesn't sound too far off between 100 and 300yds, given the velocities you're getting. My 30-06 zeroed at 175yds shows 8.4" drop at 300, and that's at a slower velocity.

Someone else here with more experience can probably shed more light on the issue, but without running your figures through a program, that's what comes to mind.

BTW, what program are you using? http://www.eskimo.com/~jbm/calculations/traj_basic/traj_basic.html seems to be fairly consistent with my expectations with the rifles I shoot.

Barnes and JBM give me around 3.5-3.8" high at 100. The scope centerline above boreline is critical. I had to drop the velocity to 2400 to get your results from both programs. My Chrony has always been coser to 30-50FPS to any I've checked it against. I have also found the programs to be far closer to actual experience than you have seen.

Ramrod, That is what I found to I had to drop the velocity to 2400 which I know is incorrect

Shoot it again at 150, 200, 250, 350 and 400yd, if you have the room, than compare the program with your reality.
Sometimes weird things happen at short ranges, esp before the bullet has completly settled down.

quote:

Originally posted by Dark Templer:
Well how many of you think ballistic programs are accurate? ...

Hey DT, Not me. They are simply randomly selected Mathematical Models of a generic chamber and barrel. Way too many variables for them to be extremely accurate.

That said, occasional flukes will occur and they can be quite close to reality. The trick is to remember they(both the Software and the Chronographs) have the potential to be misleading, regardless of how many "close" examples you happen to experience.

I have the old Load From A Disk software and it has "predicted" some very close velocity estimations when compared to a chronograph. And it also can be misleading.

I think of them as excellent ways to initially "get on the paper" at distance. Then I create my own Drop Charts, simply because I knowthat ALWAYS works.

Best of luck to you.

quote:

Originally posted by Dark Templer:
Scope height 2 inches

How do you measure this.......is it the distance from the center of the Objective (center of crosshairs approx.) to the center of the bore?
How have you guys found is the easiest way to measure this?

quote:

Hey DT, Not me. They are simply randomly selected Mathematical Models of a generic chamber and barrel. Way too many variables for them to be extremely accurate.

I agree the interal are no better than a loading manual. The external programs are close but I still measure at distance to build my own charts as well.

As to the height it is the center to center. I normally measure as best I can and then test the drop in real life. I had a buddy that made ruler and set it up with a rod in the barrel and then looked through the scope. I would think the small amount of off center of the cross hair at that distance would not make a difference.

quote:

Originally posted by captjordan:
...is it the distance from the center of the Objective (center of crosshairs approx.) to the center of the bore? How have you guys found is the easiest way to measure this?

Hey Jordan, Back when I thought it would make a difference I would measure from the bottom level of a mounted scope ring(without a scope in it) to the top of the Bolt. Then add 1/2 the diameter of the scope and 1/2 the diameter of the Bolt.

Probably the easiest is to set the rifle muzzle down on a piece of carpet. Then take a short ruler and lay it across the rear lens of the scope with no bolt in the rifle. Let the end of the ruler go to as close to the middle of the bolt opening in the receiver as you can eyeball it. Then read to the bottom of the rear lens and add 1/2 it's width.

As ramrod said, It really isn't all that critical, cause you need to verify the Drop Rate rather than going by a Software estimated drop anyhow.

Best of luck to you.