Cannot make ballistic program and POI match!

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Tumbleweed, Apr 18, 2015.

  1. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    Hi guys, I need some input and ideas here as I'm close to a loss after troubleshooting everything I know to check.
    Here's the problem:
    When I shoot at various ranges my ballistic program calls for x amount of come up based on my inputs. What I've found is that at some distances POI on target may be low (up to 1 MOA), some are spot on and at other distances (farther) POI could be as high as 1 MOA.

    The same issue is occurring with two different rifles.
    (Full Custom 300 RUM, 230 Berger at 3,210fps, Vortex Viper PST 6-24 SFP, accuracy is .25 to .5 MOA depending on me.)
    (Rem 721 300H&H, 215 Berger at 2,670fps, Vortex Diamondback 4-12, accuracy after 300 yards is inside MOA.)
    I use "Shooter" for my ballisic solutions for both weapons. I have checked Shooter against JBM Ballistics and they match almost perfect which rules out an issue with Shooter. I use a Kestrel 2500 for air density and temperature to input into Shooter.
    I have confirmed that rifles are still zeroed.
    I realize this could not be an incorrect velocity issue because I would either by consistently low or high at all distances and that's simple enough to correct for. An incorrect B/C would be easy to fix too.

    With the RUM I ran the numbers for atmosphere and found the yardage at which I would have exactly 10 MOA of drop. At 672 yards I held over with the 10 MOA bar in my PST and dead centered the 2.5" bull with two shots. Pair was 1.5". This confirmed my input velocity in Shooter was correct.

    Today I created a MOA grid on freezer paper to be able to physically check scope tracking at 100 yards. MOA lines were Zero, 2.5, 5, 7.5, 10, 12.5, 15, 17.5, 20, 25, 30, 35 and 40. I did the test several times with each weapon to get an average. The Viper PST averaged within .25 MOA at all distances. The Vortex Diamondback was also within .25 MOA out to 35 MOA of travel.

    This kind of baffled me because an incorrectly tracking scope would explain this, but the scopes appear to be fine. I borrowed my uncle's new Leica 1000 rangefinder to compare to mine thinking that my rangefinder was lying to me when setting up targets. Nope, they both match within a yard out to 1,100 yards.

    Both scopes, bases and action screws are tight as they should be. The rear of the guns are always supported well with a rear bag when shooting so as not to cause a vertical POI shift.

    Any ideas are welcome as this just does not make sense.
    Thank you!
     
  2. pyroducksx3

    pyroducksx3 Well-Known Member

    Messages:
    782
    Joined:
    Sep 27, 2009
    I tried using g7 numbers for my programs and was having trouble getting everything to match. I switched to g1 and have had fewer issues. I use applied ballistic for some of the features but it has never matched up for me to real world shooting. I have been using bulletflight for field shooting with much more success. For getting my 6.5 creedmore to match all actual drops to 1351 I had to step the bc and velocity in the advanced feature.
     
  3. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    Not familiar with bulletflight, I may have to check it out. I had thought of trying to play with G1 stepped B/C's but as a last resort. I'm not sure I could make that work anyway with POI being high at some distances and low at others. I don't know that the program could make those weird numbers jive.
     
  4. Browninglover1

    Browninglover1 Well-Known Member

    Messages:
    1,154
    Joined:
    Jan 10, 2011
    How's your form? I'm amazed how bad my vertical can fluctuate depending on how I set up my rear bag. Pressure on my shoulder, or bipod preload, can cause quite a bit of weird vertical too.
     
  5. pyroducksx3

    pyroducksx3 Well-Known Member

    Messages:
    782
    Joined:
    Sep 27, 2009
    What are your drops in moa and what bullet/cal are you using?
     
  6. cowboy

    cowboy Well-Known Member

    Messages:
    1,080
    Joined:
    Jul 14, 2007
    First of all - do the rifles repeat their come ups at the same yardages. I guess what I'm asking is are the come ups consistent on different days. If their are consistent then it points to being something in your program.

    Have you ever checked your scopes for what their "actual" click value is rather than taking it for granted that they are .25 per 100 or whatever?
     
  7. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    Well, I always try to be as consistent as I can with keeping some pressure down on the rear bag and good and snug into the shoulder. Never had this issue until recently.
     
  8. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    I have not stretched the guns out and tried to repeat the drop data, that will be next.
    As mentioned earlier, I did a tracking test on both scopes today to verify that they're doing exactly what they're supposed to do out to 40 minutes of come up. They were both within plus or minus .25 MOA when comparing the reticle with each of my lines on paper at 100 yards. It surprised me, I just knew that I had tracking issues:rolleyes:
     
  9. Greyfox

    Greyfox Well-Known Member

    Messages:
    4,457
    Joined:
    Jan 21, 2008
    I guess if everything checks out with the scope, rifle, shooting form, etc, the high-low POI variation might be the load. Have you checked the ES of your load? My buddy had a similar issue. Everything was fine with his zero, and closer range shooting. He had variations high and low, as much as 1 MOA at the longer ranges. When we checked his load, his ES was at 30FPS. He had to go to a powder change to correct the issue. Just a thought.
     
  10. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    I could see this being a problem when a load hasn't been tuned for low ES. With the RUM I've had group vertical spread under 1.5" at 1,350 yards. Typically it's around .25 MOA v/s and rarely worse than .5 MOA. The 300 H&H holds about a .75 MOA vertical spread past 300 yards. So, whetever I dial to, the groups and vertical spread are acceptable. This is just frustrating!
     
  11. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    Ok, here's some specific drop info so everyone understands what I'm talking about. Atmospheric conditions are pretty consistent this time of year. Temps around 65, air pressure between 29.95 and 30.30 and humidity between 50 to 70%.
    300 RUM 230 Berger at 3,240 fps:
    Zero at 100 yards, bullets all touch
    300 yards, shooter calls for 2.4, dialed 2.5, fired two shots with perfect elevation and less than .25 MOA vertical.
    556 yards, shooter calls for 7.4, dialed 7.5, fired two shots with less than .25 MOA vertical and pair center averages .75 MOA low.
    777 yards, shooter calls for 12.6, dialed 12.7, fired two shots with less than .25 MOA vertical and pair averages .25 MOA high.
    1000 yards, shooter calls for 18.8, dialed 18.7, fired two shots with less than .25 MOA vertical and pair averages 1.5 MOA low!
    I stopped here as there is obviously an issue.

    300 H&H 215 Berger at 2,670 fps:
    Zero at 200 yards (as best as I could with a still unstable bullet)
    375 yards, shooter calls for 4.5, dialed 4.5, fired two shots with no vertical spread and and shots were less than .25 MOA low.
    551 yards, shooter calls for 10.0, dialed 10.0, fired two shots with a vertical spread of .6 MOA and pair averages .8 MOA low.
    700 yards, shooter calls for 15.3, dialed 15.5, fired two shots with less than .25 MOA vertical spread and pair averages 1.25 MOA high!
     
  12. bigngreen

    bigngreen Well-Known Member

    Messages:
    6,210
    Joined:
    Nov 24, 2008
    Are you shooting on any terrain? All these shots on paper? Is there any hint of a head wind or tail wind?
     
  13. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    I'm shooting across flat farm field. Wind is almost always coming from 9-10 o'clock at 3-8 mph. I can't say that I remember a tail or head wind when I was shooting these drops. Yes, I always shoot on freezer paper to be able to precisely measure groups, drop, ect. Do you feel wind from the rear or front could account for this? I have to admit that I've never thought about that before.
     
  14. Tumbleweed

    Tumbleweed Well-Known Member

    Messages:
    510
    Joined:
    Oct 20, 2007
    So I think I'm on to my issue. I've ruled everything else out. Same issue with both guns? I started looking at my rear support bag. It's bad shape and I've been fighting it for a while. It has sand in it and the sand tends to fall down and I lose my support easily. Last night my wife helped me make a couple bags out of old jeans legs. We filled them clear full of rice. I tested it tonight and fired two rounds at 1K. One shot was spot on elevation wise and one 10" low. Now, my concern looking at my stock on the bag is that under recoil it may lift the rear of the stock or allow up and down rocking under recoil instead of a straight back slide. May explain one shot 10" low. What do you guys think after looking at the pic?
    image.jpg