20 MOA RAIL & JBM Question

Discussion in 'Long Range Hunting & Shooting' started by winmag, Aug 28, 2013.

  1. winmag

    winmag Well-Known Member

    Messages:
    2,528
    Joined:
    Dec 23, 2009
    Ok so a few of you probably saw my post in the Equipment section, but I'm having a heck of a time with my scope/20MOA rail.

    Equipment info:
    Semi Custom 300WSM 180 Accubonds @ 3100+FPS
    Leupold VXIII Tactical 4.5-14x40 A/O
    Leupold Custom Shop installed the Varmint hunter reticle
    Leupold 20 MOA Rail
    Leupold PRW medium rings

    I zeroed my rifle @ 200 yds.
    Checked at 607 yds with my 550 yd hold on top of target & was like 8 feet high! Woah! Adjusted scope way down. Shot 607 with my 550 yd hold on top of target & smacked it.
    Ok, I thought, something is off. Ill shoot at 300yds. With my 300yd hold. So I did @ was almost 3 feet low!
    So, re-zeroed my rifle at 300 with my 300yd hold. Moved out to 500 @ was way high again! Scratching my head, I tried my 400 yd hold on the 500 yd target & hit 5-1/2 inches low of dead center.

    I chose the Varmint hunter reticle because it matches up so close to my 300WSM, & 300Wby shooting 180's at 3100 ish for the close stuff, & figured I'd dial anything farther.
    It worked flawlessly on my 300WBY launching 180's at 3085 FPS with standard 2 PC Leupold medium bases, & Leupold rings.

    WHAT GIVES?!?
    How do I compensate for the 20 MOA rail when I'm running JBM to get close?
    Do I even need to? Or is a 200yd zero a 200 us zero like I always assumed it was?
    Very confused.
    Here's a pic of Leupolds Catalog sub tensions in print, & my 180's in ink pen.
    image.jpg
     
  2. Broz

    Broz Well-Known Member

    Messages:
    8,637
    Joined:
    Feb 3, 2007
    If you are only using reticle holdover, the 20 moa rail should not change a thing, or even be necessary for that matter.

    I don't like hold over anyway but thought I would offer what I could. May I ask why you don't just start dialing in for the longer shots? You have moa target turrets, correct? It is a fact dialing is more accurate for longer shots.

    Jeff
     

  3. kiwi3006

    kiwi3006 Well-Known Member

    Messages:
    674
    Joined:
    Aug 1, 2007
    Have you got the magnification set to the correct triangle?
     
  4. winmag

    winmag Well-Known Member

    Messages:
    2,528
    Joined:
    Dec 23, 2009
    Thanks Broz, I thought a 200yd zero was a 200yd zero, but I'm glad you confirmed it.

    I wanted to dial past 600 & have enough come ups to clear 1k with a 1" tube, thus the 20 MOA rail.
    I greatly prefer the stadia lines for the close stuff, since it saves time. Why dial on 2-500 yd shots ? Having the 550 pin is just a bonus.

    I don't mind dialing, but I'd rather range & shoot on the close stuff. I hear "I don't like the hold over thing" from a lot of folks. And that's fine. I do. I'm not afraid to dial when I get out far enough for it to matter. Unfortunately my rangefinder (Leupold RX-II) doesn't reliably range far enough to take advantage of dialing. I finally got the rifle capable of being serious at Long Range. Now I have to upgrade my ranging equipment.
     
  5. winmag

    winmag Well-Known Member

    Messages:
    2,528
    Joined:
    Dec 23, 2009
    Yep, it was one of the first things I checked when I was that far off.

    Still so confused as to what to do & how to fix this, short of having Leupold instal a standard fine crosshair, & having to dial all the time.
     
  6. Broz

    Broz Well-Known Member

    Messages:
    8,637
    Joined:
    Feb 3, 2007
    I see your point, and do not wish to de-rail your thread so I will only post this. You did ask:).

    Why? Because you are selling your rifle short by cheating it in accuracy. The difference between 450 and 500 has to be greater than 1 moa in your rifle and it is growing by the yard. There simply can not be enough aim points to keep up with the accuracy of the rifle. Plus I don't buy the "faster thing" Not if you would practice both ways. While you are finding that line among many lines, counting and rechecking, "oops it's in between those lines" ? (hope your not in between the wrong ones).. I will wheel my turret to the exact yardage and pin wheel what ever it is for dinner. I started long range with the hold over method. It worked until my rifles and I out grew it with distance.

    I can see you are reaching out farther than before. That is way cool!!! But please keep an open mind to other options, you will need to adapt in some areas. Trust me.

    I will not post here again unless I have a suggestion or idea in line with your original post.

    Jeff
     
  7. sp6x6

    sp6x6 Well-Known Member

    Messages:
    3,043
    Joined:
    Dec 8, 2009
    I have shot a system similar to your for years, B&C reticle,with CDS dial. It is faster and I never had problems. It was much easier for my 15 yr. old son to figure than dialing, he messed up the dial many times speed goat. This is before high speed, and zero stop. You should just match your drops to the listed stadia drops. Then verify, mine where always close with JBM. My son shot a speed goat at 550 with the B&C , with me spotting and short notice after a runfrom the goats, I was on lazer and would be hard to do solo. I prefer dial, but still use my tmr reticle for holds to 825. I have the mils and 1/2 marked accordinly
     
  8. kiwi3006

    kiwi3006 Well-Known Member

    Messages:
    674
    Joined:
    Aug 1, 2007
    Do you need a 300 yd zero with the 300 wsm for it to work?
     
  9. winmag

    winmag Well-Known Member

    Messages:
    2,528
    Joined:
    Dec 23, 2009
    No no no,
    I just used my 300yd pin & zeroed it at 300 so I could salvage a bear hunt last week.
    Smoked my bear at 423yds. Holding between my 300, & 400 yd pins, so it worked, but NOT how I wanted.

    I zeroed it at 200 slingin 180's at 3085 fps with my 300Wby, & it shot Great out to 600.
    So, I figured 180's at 3100+ out of my 300WSM would be quite similar. Something is not right. Even JBM says it should be right there with Leupolds Sub Tensions.
    I'm confused.
     
  10. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

    Messages:
    6,848
    Joined:
    Jun 12, 2004
    For what it sounds like your using this rifle for, hold over shooting will be perfectly fine. I admit that dialing up is more precise but if your drops are figured accurately and your not shooting much over 800 yards, hold over will be faster in the field and no chance of loosing your zero in the field either.

    I have been holding over for a long time and have taken over 30 head of big game from ranges between 500 and 950 yards with all but two taken with one shot. Those two were pilot error on the first shot which were clean misses and after correcting my mistake, the second shot were both clean kills.

    THe problem with hold over shooting at ranges past 800 yards is that most scopes have some parallax in the field of view and when your using a reference mark that is farther down on the vertical stadia of the reticle, you get some of that distortion and consistency suffers.

    For sub 1/2 mile shooting I hold over, for past I dial up. I am not saying hold over shooting is as precise as dialing up, even at moderate ranges such as 400-600 yards but its MORE THEN accurate enough to put the first shot into the vitals of a big game animal with a lot of room to spare. All comes down to getting your drops figured accurately and testing them.

    With a properly set up system, its easy to put first shot within 1/4 moa of point of aim using hold over. Now if your shooting groups, I am sure your groups would be bigger using hold over because at times you are estimating between reference points but for killing big game, it work perfectly well.

    Both systems have advantages and disadvantages. For under 800 yards, in my opinion, hold over is better for big game hunting, for over 800 yards dial up is better.

    Back to your problem, I am sure it is something simple. One thing I would do it reverse engineer your drops to see whats going on. By that I mean, for example, find what your bottom reference line is supposed to be impacting at and set a target up at that range, for example, say its 750 yards. Set a target up at that range and then basically zero your rifle with that reference line at that target distance.

    That way you know your rifle will hit on point of aim at that range using that reference point. Then work your way back and record your results. Make sure your scope is set up on the correct power. In fact from what you describe, I would say there is something off with the power setting on your scope.

    I like setting a scope up this way because it removes some of the error we see when we zero at closer ranges and then shoot at longer ranges. Just helps speed up the drop chart development. If you are zeroed at long range the error at closer range will be less and also less significant whereas a small error in sight in at close range will result in a much larger error as range increases.

    Now to your scope. The Varmint reticle is not the best for hold over shooting much past 500 yards. There is a lot of room between each reference point and they are inconsistent in spacing. A MUCH better reticle for hold over shooting is the TMR reticle and that may be something you want to look into.

    Second focal plane reticles are also not the best for long range hunting with hold over shooting because your locked into one power setting, usually the top power setting and in many cases that not the best one for big game hunting. A First Focal Plane scope is far better as reticle stays consistant with target at all power settings.

    NO problem using a SFP scope for hold over shooting, just not as flexible.

    Hold over or dial up makes no real difference, for big game hunting out to 1/2 mile or so, it comes down to what you want to use and what you are comfortable using. Both systems will get the job done perfectly well, both have advantages, both have disadvantages. Pick a system and practice a lot and you will be just fine.
     
  11. therichardpowell

    therichardpowell Active Member

    Messages:
    29
    Joined:
    Sep 20, 2012
    Have you had any luck settling this?