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Hey Pegasus (or anybody)....help me figure this out.

LinefinderLinefinder ModeratorPosts: 7,762 Senior Member
Took my 6mm Rem to the range Saturday to verify zero and comeups table prior to antelope season.

The load is: 95 grain Nosler Ballistic Tips (published BC of .379).
MV = 3250 (ES = 134, SD =37....based upon average of 30 shots chronoed over the past five years).

I fired a 100 yard three shot group that measured in the low .3's, center of group was 1.8" above POA.
I fired a 300 yard four shot group that measured .903", center of group was 2.75" below POA.
This give a vertical distance between the group centers of 4.55"
I used the same aimpoint for both the 100 and 300 yard test.
Vertical spread of 100 yard group was .25", Vertical spread of the 300 yard group was .4".

While I have not fired for the exact zero, it's somewhere between 240 and 260 yards.

In trying to verify my comeups table, nothing I key into Oehler's Ballistic Explorer yields this trajectory.
I've tweaked the BC up and down, the velocity up and down, and the zero range up and down. Nothing fits. I am using the G1 model with the NBT. Should I be using G5? (Although that didn't seem to work, either).

The differences between what I can make the program do and what the rifle actually did equate to about a 6" difference at 500 yards. Actual firing is "flatter" than what the software returns.

I've never run into this much difference before, and frankly, I'm at a loss. The only thing left that I can theorize is that while my focus for the 300 yard line was fine (actually seeing the 6mm holes in the target), possibly my parallex was off a bit?

Any ideas or theories?

Thanks.

Mike
"Walking away seems to be a lost art form."
N454casull

Replies

  • jbohiojbohio Senior Member Posts: 5,615 Senior Member
  • PegasusPegasus Senior Member Posts: 2,830 Senior Member
    I went to JBM and played with the sight height.

    If I use 2 inches as the height of the scope over the center of the barrel and use their stored numbers for the Nosler Ballistic Tip 90gr in .243 at 3250 and a zero at 250, I get 1.7 above at 100 yards and -2.9 at 300 yards. I used 5000 feet as elevation. Their stored BC value is .365 G1.

    If your scope is perfectly focused for the 300 yard line and you see the reticle very crisply, there is no parallax.

    I sure hope I read your question right; it's been a long day.
  • LinefinderLinefinder Moderator Posts: 7,762 Senior Member
    I'll check the scope height. I had the program set at 1.5", which is what I believe I measured on the rifle.

    Your numbers are "pretty much" what my program was returning. I used 4500 ASL, 60F.

    This is, of course, close enough for pdogs (and for that matter, probably antelope), but a 500+ yard shot on a goat isn't out of the question this year, and that 5" difference at 600 yards kind of bothers me some.

    Mike
    "Walking away seems to be a lost art form."
    N454casull
  • PegasusPegasus Senior Member Posts: 2,830 Senior Member
    I redid the calculation with 4500, 60, and 1.5. The 100 is 2.0, the 300 is -3 and the 600 is -53. When you measure the scope height, I am quite sure you know is the distance between the middle of the scope and the middle of the barrel (chamber). However the zero distance is also quite important, as I'm sure you are aware.

    Edited to add; at 2.0 with 4500 and 60, the 100 is 1.7 and the 300 is -2.9. Zero is at 250.
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