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MV Truing Troubles

GreenCanoe

Private
Minuteman
Jun 21, 2018
53
44
Desert Southwest
New guy here, been looking around for a while but ran into a wall and need some help.

Took the rig out last weekend, looking for hits out to 1k. I knew I would need to true the measured MV to reflect real world performance because that's just how it goes. Zero was confirmed at 100 yards, calculations were solid at 782 yards (POI may be a tad low, mirage plays with me sometimes) but when I go out to 1,076 yards the data says to dial up 9.7 mils, and nothing. I do the stupid thing and dial up more thinking I must have mil'd the target too close, and still nothing. After an hour and multiple trips to the target and back I put the smooth brain away and decide to dial down to 8.7 mils, then fire off another at 8.2 mils. Next trip to the target shows 2 holes, spaced about 1/2 mil apart (ending up about .3 mils high of target waterline). "Okay, that's odd" I think to myself, but it be what it be and hits don't lie. I shoot a 3 round group to confirm at 8 mils then go home to reevaluate my life decisions and play with the calculator only to find out to adjust POI to reflect ~7.7 (where the waterline is) I have to adjust MV from 2697 to 2988! At this range my bullet is still supersonic, so I haven't adjusted BC, but in trying it just for the sake of fun I found out I'd have to move the BC from .301 to over .410, which simply can't be.

Where have I gone wrong? Scope tracks beautifully, so I don't think it could be that. Muzzle velocities are expected to be a little off, but not by THAT much! Please see below for all relevant data.

Rig:
Tikka T3 CTR .260 Rem
KGB Bravo (AICS Mags)
Harris 6-9" (that's what she said)
Vortex Viper PST Gen 2 (Leveled)
Weaver Rings & 20 MOA Base

Ammo:
142 gr Sierra SMK (1742C)
43.0 gr. Hodgdon H4350
CCI BR-2 Primers
Starline Brass
Base to Ogive @ 2.409" with an average OAL @ 2.027"

Magnetospeed V3 Avg MV @ 2697fps / 8.3 fps Standard Deviation

Weather:
D.A.: 4350
Station Pressure 26.16
55.2 Degrees American
25.5% Humidity

Thanks to anyone who can help out, I'm just confused.
 

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Did I understand you correctly that you determined the 1076 yd range using your reticle?
 
That is correct, yes. I'll take a measurement along the horizontal axis, do the math, then take a measurement along the vertical axis and math for that one. Somewhere in between the two of them will be the correct answer and if they both agree then that just makes it simpler. Are you thinking I'm just off by .1 or .2 mil in my measurements?
 
Well, let's go through the math. Using a couple assumptions in addition to your data (I assumed 8-twist barrel and 1.5" sight-over-bore), the Hornady 4DOF program calls for 9.50 mils at 1076 yards. This is slightly different from your reported 9.7, but close enough for this exercise.

At 1076 yds, your 31"x62" target should mil out at 0.8 mil horizontal and 1.6 vertical. But let's say that it's actually 0.85 mil by 1.7 mil (i.e., you got it very slightly wrong in the scope). That'd make your actual range 1013 yards, and at that range your dope comes out to 8.62 mils, or 0.9 mil less on the turret than at 1076 yards.

It seems far, far more likely that you were off by 0.1 mil in the scope in the vertical and 0.05 mil in the horizontal with your target over 1k yards away in the mirage that you mentioned, than it does that your MV is off by almost 300 fps (it's not) or that your BC is ~30% higher than reported by Sierra (it's not).
 
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Once you made that suggestion I did a little more looking myself, and I have to agree with you - It's FAR more likely that I missed my measurement than all the calibrated measurement devices are just wrong (and that BC was using Litz's report). That was the most convincing 0.8/1.6 I've ever seen, but that's the only plausible explanation here. Thanks for the help and I guess I'll go out and practice some more!
 
If you eliminate the known variables, it looks like the issue is an unknown variable. You need to invest in a range finder or shoot at known range until your data is trued. Even trained Scout/Snipers struggle milling for distance past 800 yards or so.
 
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Once you made that suggestion I did a little more looking myself, and I have to agree with you - It's FAR more likely that I missed my measurement than all the calibrated measurement devices are just wrong (and that BC was using Litz's report). That was the most convincing 0.8/1.6 I've ever seen, but that's the only plausible explanation here. Thanks for the help and I guess I'll go out and practice some more!
I'm with @Long Range 338 on this one: if you're serious about shooting that far, you need a range finder. Depending on your range situation, you can consider borrowing one and setting up targets at known distances, but yeah, if you plan to do any kind of changing distances that far out, you need a decent LRF, no question.
 
If there are clearly visible landmarks or terrain features where you shoot try and measure the distance on google maps.
 
What rangefinders are reliable to that distance (and beyond)? I have a monarch gold 1200, but anything beyond 600 it's less than ideal. Especially with no zoom it's hard to center crossbars on a target that small.
 
Did I understand you correctly that you determined the 1076 yd range using your reticle?
👆
OP
You really can reticle range accurately enough to be truing a solver at that distance.


What rangefinders are reliable to that distance (and beyond)? I have a monarch gold 1200, but anything beyond 600 it's less than ideal. Especially with no zoom it's hard to center crossbars on a target that small.
Lots of great LRF for reasonable $$$

A good rule of thumb is to half the number on the range finder and that a realistic range to get consistent results.
 

Here's one, can't speak to the function but I'm sure you can find plenty of reviews online. Amazon has this for $500 more, so it's definitely a solid price.
 
yeah...it'll getcha!


Here's one, can't speak to the function but I'm sure you can find plenty of reviews online. Amazon has this for $500 more, so it's definitely a solid price.

I did end up grabbing that LRF, but I'm not giving up on training the eye to MIL as correctly as possible. It almost seems like cheating, having a range and solution presented to you through that thing...I'm going to miss my calculator and notepad. lol
 
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yeah...it'll getcha!



I did end up grabbing that LRF, but I'm not giving up on training the eye to MIL as correctly as possible. It almost seems like cheating, having a range and solution presented to you through that thing...I'm going to miss my calculator and notepad. lol
Nothing wrong with wanting to keep a skill sharp. Listened to a podcast the other day and one of the guys was saying (not for the first time) that it took him a long time to decide to jump into the game aspect of PRS with both feet, since he came from a hunting and military background and he felt that if it wasn't practical then it was a little silly. Meanwhile, dudes who are lesser shooters are scoring higher because they committed to the game haha.

Not saying one is wrong or right, but if it feels like cheating, consider shooting a match, either with provided ranges or unknown distance ("UKD"). At either of them, you'll find folks either ranging or just accepting the provided ranges because they need that to be fast and correct to be able to complete the CoF. When you can barely finish a COF (or can't) even with known ranges, it stops feeling like cheating real quick lol.

Good luck!