Rifle Scopes Using a MK4 Second Focal Plane hashes at minimum power

[ColoYooper]

First, let me begin by admitting that I now appreciate the value of a First Focal Plane scope while attempting to compete at this years SnipersHide Cup. I was using a Leupold MK4 8.5x-25x, 50mm scope on a 300WM and there is no way in heck to control the recoil sufficiently to observe the shot hit/misses at 25x...even with a really good brake. And with variable wind conditions of 30-50mph crosswinds, I NEEDED to be able to hold off the target by some known amount using the MIL hashes in the reticule. I purchased the scope several years ago, and I'm not motivated enough to replace it with a FFP scope...yet. Following the match, I returned to the range and found that I could effectively engage targets from 300 yards to beyond 1000 yards at the minimum 8.5x setting and SEE THE HITS/MISSES. OK, now I've just got to figure out what the hash marks represent at the minimum 8.5 power (they are MILs at 25x). Easy enough: given there are 3.43777 MOA per MIL, if we divide the Max power of 25.0 by the minimum power of 8.5 and convert to MOA by multiplying by 3.43777 we come up with 10.111 MOA per Hash line (the half hash marks are 5 MOA). I'm certain it wasn't an accident that Leupold choose the 8.5-25x range, but this is the first I've ever heard that one could interpret the hash to be 10 MOA spacing at the minimum power of 8.5. Anyway, using the Shooter app during the competition I can easily obtain both MOA and MIL solutions for windage holdoff, so its not that big a deal. (granted 5 MOA is a bit coarse, but I'll play with it a bit longer before I drop more $$$ on a new scope.)
ColoYooper

 

[SomeOtherGuy]

FYI, Leupold's specs indicate that actual magnification is 8.20x at the low end and 25.1x at the high end. That will change your calculations slightly. The best bet is just to put a yardstick (etc.) up at a 100 yard distance target and then calibrate your reticle measurements at low power and any intermediate power you might want to use. It's the only way to really be sure.

Mark 4 LR/T 8.5-25x50mm (30mm) M1 | Leupold

There's a number of good FFP scopes you could buy for the price of the resale value of your Mark4.

 

[doc76251]

The best bet is just to put a yardstick (etc.) up at a 100 yard distance target and then calibrate your reticle measurements at low power and any intermediate power you might want to use. It's the only way to really be sure.

This is the correct answer. The hard stops at either end of the power ring are the only TRUE points you have. If it was me I'd be checking the top end for the correct line spacing also. Not that I have ever seen 7 out of 10 Leupy scopes unable to be dialed to the correct subtention in one class on one day.

Cheers,

Doc

 

[ColoYooper]

Thanks for the insight. I guess Leupold wasn't as clever as I initially thought. I'll do the yardstick calibration, but I expect that calibrated primary hashes at 8.20x of 9.5 to 10.5 inches at 100 yards (SomeOtherGuy's numbers would predict 10.5") are within my ability to integrate wind at distance and to apply that wind holdoff using course hashes of ~ 5 MOA. I doubt that I'll be changing the MK4 scope on my target 300wm rifle...but I might be even more motivated to add a 6.5 Creedmoore with a FFP scope to my collection.

 

[ColoYooper]

If you re-read my initial post one might find (perhaps not everyone) that I had a "really good brake". Unfortunately, I am unable to consistently observe bullet impacts at "half power" at less than 600 yards. Perhaps I'm not the stud you are. Finally assuming the half hashes equate to 5 MOA at the minimum power, there is no fucking math involved other than approximating a span of say 3 MOA within a 5 MOA hash span. And yup, I'm lucky enough to have the TMR reticle on this rifle. But since I also use this for benchrest competitions, I'm happy with the existing MK4 scope.