*****need help with my leupold mk4*****
 

I recently purchased a Mark 4 LR/T 8.5-25x50mm (30mm) M1 Illum. Ret (TMR) and mounted it to my standard M1A. I've gone through 200 rounds of 168 gr .308 factory ammo (Nosler Trophy Grade) trying to get this thing dialed in.

When I originally zeroed the scope at 100 yards, I did so on full magnification and achieved a 1 inch shot group on center. I was hitting about 2-3 inches low at 200 yards (which is about right per the ballistics).

I have since been back to the range, because I wanted to zero the scope at 200 yards instead of 100. My first shot was 8 inches low on full magnification. Subsequent shots were all over the place (after adjustments were made).

I decided to back off back to 100 yards and re-confirm my zero. The full magnification was giving me a hard time locking down a shot group and getting on center. I decided to back off on magnification and put the scope on it's lowest power. My first three shots were a 1/2 inch group, and my adjustments to center were spot on after the first adjustment. I was repeatedly hammering 1/2 inch shot groups on center on low power.

But then I'd go back to high power and my shots would just be all over the place. The Marine Corps taught me how to shoot. I have several other scopes. This isn't my first rodeo...but what the heck is going on here? Could it be a faulty scope?

Your help would be much appreciated.

probably a parralex problem on high power, research how to set the focus for zero parralex. my 8.5x25 mark4 is pretty sensitive as far as the focus
RR

I believe Ridge has something here.....................


Can you adjust your scope for parallax - Did you ?

I've taken dozens of folks out to shoot deer at extended range, They all agree the hardest part of it is setting the focus. one guy missed 3 shots at a deer at 787 yards, he said he thought I had screwed up figuring the drops, I got on the rifle and set the focus, gave it back to him and the next shot.....bang/flop, it will make you miss and miss bad!
RR

Ridge has the comm, so I won't add much in terms of the effect of parallax on POI vs. 'perceived POA' except for a couple of pictures I put together a few years ago to illustrate the effect of parallax setting error.

First off, the parallax setting on your scope is a control that focuses the crosshair image in the same plane as the target image as light passes through the scope. If the parallax is set properly, no matter how the shooter's eye is positioned, the images of the crosshair and the target will stay locked together, as depicted that the image inverts perfectly in the plane of the reticle (top case). If the parallax is incorrect, but the shooter has PERFECT eye alignment, it will still make the hit (center case). If the shooter has a parallax error and 'less than perfect' eye position, the crosshairs will appear to drift proportionately around the target. The bottom case shows how if the eye isn't aligned, even if the scope IS on target, the crosshairs won't appear on target, so the shooter would move the crosshairs to center on target, but they'd be inadvertently moving the rifle OFF of target.

(This isn't exactly correct, but for all intents and purposes, the theory is there).



To illustrate this, I took these photos below. This scope is set up, intentionally, with parallax errors and imperfect "eye" position, at 10yrds. The red dot at the bottom at the bottom of the target is a laser boresighter, intended to show that the rifle was not moving in the rest, even though the crosshairs clearly move around the target:



Without that parallax error, the crosshairs would not move around the target like they do in this series. I've DRASTICALLY exaggerated the extent of the eye position misalignment to better show the drift, as no shooter would ever fire with the 'moon shadows' in their scope like these examples, BUT, smaller misalignment errors aren't so obvious, and still have dramatic effects on the relationship between POI, POA, and PERCEIVED POA.

You can see at +/- 1/2" drift in these photos, only at 10yrds. At 100yds, that's an extra 10" of error in your groups, at 200yrds, that's an extra 20" or more.

Of course, that's EXTREME misalignment of the eye position, but if you shoot with even 10-25% of that degree of error in your eye position, that could yield 2-4" of additional error in a 200yrd group, even though the rifle isn't moving and the shooter's fundamentals aren't changing.

As has been said, when you change the magnification, ALL scopes have a drift in parallax, some more than others. All it takes is a quick second of shifting your eye side to side, top to bottom, and verifying that the crosshairs don't drift on target, and a second to ensure that the crosshairs AND target show up perfectly focused together.

Nomercy explained it way better than I could but I will add, that 3/4"parralex error at 10 yards would equate to 37.5" at 500, 75" at 1000 yards, as I said it makes ya miss bad!
RR

I put those pics together a few years ago, figure I gotta use them every now and then to justify having them taking up photo hosting space!

After I started experimenting with parallax in college, I started wondering if maybe that wasn't a contributor for why so many factory rifles have gotten a bad rap for inaccuracy over the years. It makes such a pronounced difference in shot placement reliability that it'd be really easy for a fixed parallax scope that's either improperly focused at the factory or shot at a range other than it's factory setting, or an AO or SF scope that doesn't have the adjustment labeling timed correctly, guys could throw really bad groups even from really good rifles and really good glass.