Home Forums Hunting & Shooting Ask The Gunwriters How "accurate" are online ballistics calculators?

[quote=Mule Deer]

Yep, centerline to centerline.

I’m flummoxed (never got to use that word till now) I know in my heart (and brain) the load shouldn’t be behaving like this. This rifle is dead nuts accurate, the scope is a nice Schmidt that has never given a moment’s trouble. I’ll get back out there and see what I see. Our range there has benches at 100, 300, 400, 500 and 600. I’ll load up more ammo and give it a go and see what happens. May do the same with my 338 since I’m shooting North Forks in it and had to take a SWAG at the 338/225gr BC.

Are you sure that the 100 yd zero is exactly 2" high? And was it shot from the same position (i.e. benched vs prone for example)?

If you're truly hitting 9" low at 400 yd, you should be very close to zeroed at 300 yd and ~3" high at 100 yd. It might be worth verifying at 100 and 300, something may have shifted.

Also, kind of a side note but why is your scope mounted so high, and are you certain it's actually 2" above bore centerline? That's about 3/8"-1/2" higher than a common scope mounting that gets the scope close to the barrel.

I reverse engineer most times, and very seldom shoot at 100 yards. Everything I shoot has a 200 zero, so I get fairly close at 200, and move straight to 300 to fine tune elevation and windage, then drop the scope clicks back for the 200 zero, and set it.

I'll often shoot at 600 to zero, and work back.

Shoot a couple of shots at 100, 200, 300 and then 400 and see if anything jumps out at you. 4" off at 400 yards is a lot. I don't think 1 MOA is acceptable as a margin of error. Bad algorithm or bad data.

It is the reverse Coriolis effect in Georgia, obviously. That's why left handed quarterbacks easily throw for national championship wins. (wink)

I should seriously just read and let the adults discuss this. I'm just getting started down the path of long range shooting.

Repent while you still can!

I am not a long shooter but enjoy these apps as entertainment. Good for side by side comparisions. Brian Litz is a pro- literally on these things. Any hunting loads must be verified under hunting conditions however, imo. No exceptions .

well?

Headed out to the range tomorrow (or Monday) to check things out. Been so dang windy here I might wait a day or two for calmer conditions.

At 400 yards, a 4"+ discrepancy is quite a bit. If you are certain of your 100 yard zero, and the chronograph, then I would check the subtensions on your reticle if using dotz (using a target that you create). Then check parallax at 100 & 400 yards.

In literally dozens of rifles, I've yet to see one that did not match JBM out to 400 unless there was an obvious issue with the rifle/load combo and/or the shooter. Some used scopes with a duplex, some with dotz, and others with turrets. In all cases, the rifles have been on the money, except one.

That one oddball was a parallax issue that showed up most noticeably at 300 yards shooting slightly downhill. It turned out to be an issue with the reticle focus, and we were able to find a setting where the reticle was focused and parallax minimized for all distances out to 600 yards.

Good luck.

Jason

You can also get Litz's BCs by using his ballistic app, "Applied Ballistics." It has an extensive bullet library including th Nosler 150.

JBM has Litz BC for many bullets including the 150BT.

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

Using Magnetospeed for 400yd shots? That will change POI. Just tossing it out there.

Not to derail the thread, but how do you properly measure the distance from center of the bore to the center of the scope? I will need to be doing this myself soon, so thanks in advance.

Dan

On 700's, I just measure from the blowhole on the side to the scope rings intersection.

I don't fret measuring to the 4th digit........

Or if the back of your bolt is concentric you can open the bolt and slide it back so it's even with the ocular and just lay a ruler across both and eyeball the center of each for your measurement.

Barometric pressure? A high or low pressure system can affect the relative air density by thousands of feet...??

I’m guessing a parallax issue, or if using a MS to measure velocity, that’d do it as well.

Hmm...fed my same info into this this website's ballistics calculator and with a 3" above zero at 100 yards I got 9.7" drop at 400.....much closer to my real world findings last week.

Used Magnotospeed once. It's my friend's.....glad I never bought one. Using ProChrono digital, which may or may not be dead on, but I assume it is. I know, it's not a Ohler or a Labradar, but its close I bet.

Be absolutely certain about two things:

1.) Velocity
2.) Height above or below POA.



Travis