Confusing Balistics

[TnTurk]

OK...let's see if I can get this right so maybe someone can give me some insight as to what's going on. FWIW, this is not my gun but I did witness the shots and even shot a couple of groups to verify what was happening.
-Ruger Precision .308, Vortex Viper PST 6-24x50, 175 gr. Sierra Matchking, 43 grains of IMR 4895, Federal 210 primers, Winchester brass
Gun was zeroed dead on at 100 yards and shot .625 inch moa 5 shot group. Next, we shot it at 200 yards and it printed 1.5 inches low with a 1 inch moa 5 shot group. At 300 yards it printed 12.50 inches low (2 shots) and 15.25 inches low at 400 (4 shots). At this point we were not as concerned with moa groups as we were with the lack of bullet drop at those distances. Also, he said he had a 7 moa hold over at 400 yard and the bullet drop was only 15.25 inches. All distances were ranged. We do not have a chronograph so no idea of what the velocity may have been.
We are by far experts but those bullet trajectories seem very odd to say the least. Any help or insights are much appreciated. God Bless

 

[infoman jr.]

Quickload puts that load at 2550 fps. You keep using moa and inches in a weird way, and that may be confusing the situation. A one inch group at 200 is different than a 1 moa group at 200. My best guess is he was reading his reticle incorrectly.

Anyway, here's your ballistics table assuming a 2.5" bore-to-optic centerline.

 

[mr.big]

were all groups fired without dialing in any dope,,were you shooting up or down hill and was there a tail wind?? was the sun coming in and out from behind the clouds,,how high is your scope mounted,,

your numbers arent far off to 300 yards but you should have 26-30 inches of drop at 400,,

 

[Jcalder]

It's a dumb question but is his scope sliding in the rings. I've punched some numbers into a ballistics calculator and I can't get them to align. Best guess is 2850fps with playing with numbers. Also how high is the scope and does the rail have moa built into it. I don't know how that effects things on the short range.


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[DaveB]

Interesting thread.

We know something is not right because the physics are wrong.

 

[GOODWIN]

My guess is his "hold over" as you referenced was wrong for the 400yd group. 1-2-300yds look valid.

What was his technique when shooting the 400?

 

[TnTurk]

Infoman, sorry for any confusion. I see what I did now. Those are the numbers we expected as well with the 2.5 above bore centerline.

Mr. Big, we were shooting on flat ground, cloudy with almost no wind. I'm pretty sure he didn't dial in any dope. The first four shots at 400 were a dead on hold just to determine how much drop it would be. The difference between the poa and poi was only 15.25 inches. That's what's weird.

Jcalder, I think I answered your first question, but I don't know about the rail having moa built into it.

I really appreciate the responses gentlemen.

 

[TnTurk]

My guess is his "hold over" as you referenced was wrong for the 400yd group. 1-2-300yds look valid.

What was his technique when shooting the 400?

Shooting prone off a bi-pod and rear sand bag.

 

[TnTurk]

Question: Since he was shooting prone, would it make much difference if the target was higher off the ground that his barrel? Target was about 36 inches off the ground.

 

[Nsghunter]

were all groups fired without dialing in any dope,,were you shooting up or down hill and was there a tail wind?? was the sun coming in and out from behind the clouds,,how high is your scope mounted,,

your numbers arent far off to 300 yards but you should have 26-30 inches of drop at 400,,

I'm going out on a limb here; he stated he had a 7 MOA holdover at 400 yds., wouldn't that translate to around a 28 inch hold over at 400 yards?

7 MOA= 7 inches ( roughly) at 100 yards than 7 x 4= 28 Inches (roughly)

I am very new at this and only learned what I know from the forum members so this may be completely wrong.

 

[GOODWIN]

Yes the "hold-over" at 400yds is what is confusing

 

[mr.big]

sounds like he used the correct holdover at 400 but hit higher than expected,,

I would advise starting over and make sure everything is tight and reshoot the the string and actually dial in the dope instead of holding over and see how it goes,,

what scope is he using and what reticle does it have,,just wondered how he knew he was holding 7MOA,,if it is a second focal plane reticle and he changed the power between yardages it would change the holdover in a SFP scope,,

 

[TnTurk]

sounds like he used the correct holdover at 400 but hit higher than expected,,

I would advise starting over and make sure everything is tight and reshoot the the string and actually dial in the dope instead of holding over and see how it goes,,

what scope is he using and what reticle does it have,,just wondered how he knew he was holding 7MOA,,if it is a second focal plane reticle and he changed the power between yardages it would change the holdover in a SFP scope,,

He is using a Vortex Viper PST 6-24x50 FFP scope with the EBR-2c moa reticle.

 

[infoman jr.]

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[TnTurk]

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That's the one.
We will shoot another series of shots when we get another good day and see what happens. I still think it was operator error if you know what I mean. :smash:

 

[waterfowlwidowmaker]

Otherwise unexplainable issues are usually attributable to a loose nut behind the trigger, at least in my experiences.

 

[TnTurk]

Otherwise unexplainable issues are usually attributable to a loose nut behind the trigger, at least in my experiences.

Good to Know. Thanks for the tip.

 

[mr.big]

yeah man,,shot the whole ordeal over and put the dope in on the knobs and hold dead on and see how it goes,,it is easy to hold on the wrong line or between the wrong lines on those reticles,,I do like the hash marks to spot misses with and know what to do on the next shot but I like to dial in my elevation,,but do hold off for wind sometimes,,

 

[waterfowlwidowmaker]

Otherwise unexplainable issues are usually attributable to a loose nut behind the trigger, at least in my experiences.

Good to Know. Thanks for the tip.

I should have put "personal" in front of "experiences" in my original post. I wasn't making any inferences as to you or your buddy's shooting prowess, just my feeble attempt at humor.

 

[TnTurk]

Otherwise unexplainable issues are usually attributable to a loose nut behind the trigger, at least in my experiences.

Good to Know. Thanks for the tip.

I should have put "personal" in front of "experiences" in my original post. I wasn't making any inferences as to you or your buddy's shooting prowess, just my feeble attempt at humor.

:tu:

 

[Hunter 257W]

From the original post it seems as if the goal of shooting at longer ranges was to see what the trajectory is for this load. If you want to do that, you need to simply hold the crosshairs on the same aim point at all ranges and see where the point of impact is.