Range Report OK big diff from calculator and actual dope?

[Garvey]

Saturday 20 Nov. a Hide member and I did some shooting. When I set up steel at 600 yards and dialed in the 4.2 MIL that JDM calculated I was, in the end, .6 MIL too high. He and I spotted the shot and each read about .5 MIL. .6 MIL down got me centered on target for repeated shots. So in the end my correct dope was 3.6 MIL @ 600 yards (of course I recorded this when it was discovered) His calculator gave data that my load had to be leaving @ 2900fps +. "No way" we both said. I chronographed the load at 2740fps. The calculator gave a closer dope for 700 yards but was still .2 MIL high.

Did I enter something into the calculators wrong? I've played with sight height since I though that's what it was and I can't get it to match with actual MIL correction.

BC .462
168gr. (yes I have 175s but I'm shooting up these 168s, and won't order more)
2740fps
100 yd. zero
500' elevation
70F

(this load will hold sub MOA, also)

What gives?

 

[Bevan]

Re: OK big diff from calculator and actual dope?

Zero off, chrono numbers wrong, scope clicks not right, up or downdraft wind

 

[Garvey]

Re: OK big diff from calculator and actual dope?

Zero is good, I can chrono the load again I was going to anyway because I agree with you. I still need to box test the scope. The wind was left to right 7 to 10 mph. I wouldn't think it would've caused an updraft but I'm no meteorologist.

 

[Bevan]

Re: OK big diff from calculator and actual dope?

What's the scope? what's the terrain like? can cause an updraft downrange

 

[Bevan]

Re: OK big diff from calculator and actual dope?

also was it on an angle. would cause you to hit high.

 

[Short-bus]

Re: OK big diff from calculator and actual dope?

Use station pressure rather than elevation, you're BP can vary rather wildly depending on the weather, and his time of year it can be a little nuts. My normal shooting spot has varied from a DA of 720' to 2400', that can cause enough of a change at 600 yards to give you some headache's.

I always like to use multiple ranges to get my velocity if i'm just too lazy to chrono it. I'll get my dope at 300, 600, and 700+ and do it the same day and hopefully same weather conditions. Also record any zero shift, meaning if you're zero is slightly high or low, that'll have to be accounted for.

The other option (and the best one IMO), is to buy a butt load of 175's, and a FDAC, and trash the calculator as you'll never need it again (for inside 1,000 yards). Once you go FDAC, you'll never go back.

Branden

 

[mm509]

Re: OK big diff from calculator and actual dope?

Use the G7 ballistic coefficient. We did some shooting this last weekend, experimenting with different ballistic calculators and essential variables. It was quite an eye opener!! I have had calc's that put me spot on out to 1000y and calc's that had me miss by nearly 2 mils.

Alot to be said about actually getting out and getting real shooting data.

 

[edward r homeyer]

Re: OK big diff from calculator and actual dope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dust_Remover</div><div class="ubbcode-body">Use station pressure rather than elevation, you're BP can vary rather wildly depending on the weather, and his time of year it can be a little nuts. My normal shooting spot has varied from a DA of 720' to 2400', that can cause enough of a change at 600 yards to give you some headache's.

I always like to use multiple ranges to get my velocity if i'm just too lazy to chrono it. I'll get my dope at 300, 600, and 700+ and do it the same day and hopefully same weather conditions. Also record any zero shift, meaning if you're zero is slightly high or low, that'll have to be accounted for.

The other option (and the best one IMO), is to buy a butt load of 175's, and a FDAC, and trash the calculator as you'll never need it again (for inside 1,000 yards). Once you go FDAC, you'll never go back.

Branden </div></div>

What is FDAC? Thank you.

 

[BobinNC]

Re: OK big diff from calculator and actual dope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Halligan</div><div class="ubbcode-body">Saturday 20 Nov. a Hide member and I did some shooting. When I set up steel at 600 yards and dialed in the 4.2 MIL that JDM calculated I was, in the end, .6 MIL too high. He and I spotted the shot and each read about .5 MIL. .6 MIL down got me centered on target for repeated shots. So in the end my correct dope was 3.6 MIL @ 600 yards (of course I recorded this when it was discovered) His calculator gave data that my load had to be leaving @ 2900fps +. "No way" we both said. I chronographed the load at 2740fps. The calculator gave a closer dope for 700 yards but was still .2 MIL high.

Did I enter something into the calculators wrong? I've played with sight height since I though that's what it was and I can't get it to match with actual MIL correction.

BC .462
168gr. (yes I have 175s but I'm shooting up these 168s, and won't order more)
2740fps
100 yd. zero
500' elevation
70F

(this load will hold sub MOA, also)

What gives?
</div></div>

The most likely reason is that your target was really not at 600 yds (more like 535-550 yds), or your target was not on the same elevation as your firing position.

A 168 gr Sierra @ 2740 FPS will drop around 4.2 MILS ( + or - 0.1 MILS) @ a MEASURED 600 yds. No magic will make them drop 0.6 MILS less.

Bob

 

[Lowlight]

Re: OK big diff from calculator and actual dope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: J.J. McQuade</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dust_Remover</div><div class="ubbcode-body">Use station pressure rather than elevation, you're BP can vary rather wildly depending on the weather, and his time of year it can be a little nuts. My normal shooting spot has varied from a DA of 720' to 2400', that can cause enough of a change at 600 yards to give you some headache's.

I always like to use multiple ranges to get my velocity if i'm just too lazy to chrono it. I'll get my dope at 300, 600, and 700+ and do it the same day and hopefully same weather conditions. Also record any zero shift, meaning if you're zero is slightly high or low, that'll have to be accounted for.

The other option (and the best one IMO), is to buy a butt load of 175's, and a FDAC, and trash the calculator as you'll never need it again (for inside 1,000 yards). Once you go FDAC, you'll never go back.

Branden </div></div>

What is FDAC? Thank you.</div></div>

Field Density Altitude Cards, like a mil dot master for DA.

Adaptive makes them. Do a search in equipment.

 

[Greg Langelius *]

Re: OK big diff from calculator and actual dope?

The math works if the numbers are right.

Unfortunately, where the numbers are taken has to be considered a local value, and the longer the trajectory becomes, the less relevant those local numbers become over that entire trajectory.

Winds in particular, and this includes head and tailwinds.

Yes, head/tailwinds affect vertical drop. Not by generating any mystical 'lift' forces, but by simply altering time of flight, which impacts directly on gravity's process of generating that drop. Fly longer, fall further, and vice-versa.

Not saying unrecognized head/tailwinds are responsible for the differences you're experiencing.

I <span style="font-style: italic">am</span> saying that in addition to other factors, they are probably affecting the drop everyone experiences, unless they live and shoot either in a vacuum, or in a region where the wind never stirs at all.

I don't and I suspect very few of the rest of us do, either.

Greg

 

[Short-bus]

Re: OK big diff from calculator and actual dope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: J.J. McQuade</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dust_Remover</div><div class="ubbcode-body">Use station pressure rather than elevation, you're BP can vary rather wildly depending on the weather, and his time of year it can be a little nuts. My normal shooting spot has varied from a DA of 720' to 2400', that can cause enough of a change at 600 yards to give you some headache's.

I always like to use multiple ranges to get my velocity if i'm just too lazy to chrono it. I'll get my dope at 300, 600, and 700+ and do it the same day and hopefully same weather conditions. Also record any zero shift, meaning if you're zero is slightly high or low, that'll have to be accounted for.

The other option (and the best one IMO), is to buy a butt load of 175's, and a FDAC, and trash the calculator as you'll never need it again (for inside 1,000 yards). Once you go FDAC, you'll never go back.

Branden </div></div>

What is FDAC? Thank you. </div></div>

http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2178317&page=1

Like LL already mentioned, but don't bother reading the thread, just place your order and never look back as you'll never need to.

I was out last week and was doing some UKD (mil ranged, no LRF until after the shots) and it was spot on (after I got the right card with correct velocity in). I went all the way back to a measured 1,000 yards to see if it was just as accurate out there as it was at the shorter distances, and it was spot on. Just like my sig line says, once you go FDAC, you never go back.

Branden

 

[Garvey]

Re: OK big diff from calculator and actual dope?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bevan</div><div class="ubbcode-body">What's the scope? what's the terrain like? can cause an updraft downrange </div></div>

Bushnell Elite 4200 FFP, MIL/MIL 6.5-24 x 50.

The terrain is an extremely flat field that is used for hay ground. Obviously the hay has been cut, raked, baled, and stacked this time of year. We were prone on a burm that is about 6' higher than the field, and the target was 3'6" off the ground 600 yards away. The 600 was laser ranged with a Swarofski and a Nikon each giving 599-600.5 yards.

 

[azimutha]

Re: OK big diff from calculator and actual dope?

Out to 600 yards under the conditions you described, using a G1 BC instead of a G7 BC won't make much difference - not .6 mils anyway. Seems to me you may not have had a good barometric pressure reading, although at 500 ft. you pretty much have the luxury of using corrected pressure (if there's a reliable source nearby like an airport). Still, I would verify that. Also, chronographs can be wrong.

 

[Garvey]

Re: OK big diff from calculator and actual dope?

We went shooting again Saturday. The problem is a scope tracking problem, I believe. At 600 yards a 175 SMK was making hits, again .6 MIL less than what the ballistic chart calculated it should be. In other words the calculator gave 4.2 MIL at 600 yards but my scope dope was 3.6 MIL.

However; the calculated dope at 700, 800, and 900 yards was only .1 MIL off needed scope dope, and calculated dope at 1000 was correct for load-rifle-scope.

I think I need to call Bushnell.

 

[BobinNC]

Re: OK big diff from calculator and actual dope?

Halligan,

I'm sorry for your troubles, but I really doubt it is your scope. Yes, scopes go bad and don't track correctly. But they don't have a large error @ 600 yds (14 %), then a small error @ 700, 800, and 900 yds, followed by zero error @ 1000.

When tracking goes bad, they under track or over track each click. They don't go bad @ 600 yds, and become right again @ 700.

What does your dope do compared to calculated @ 500, 400, 300 and 200 yds. Right on or off????

I still think your 600 target is not 600 yds away.....One sure way to tell is to shoot @ 600 yds, but use only your reticle. That is use a 4.2 MIL reticle hold, with your elevation dial set on it's 100 yd. zero. If your still 0.6 mils high with a reticle hold, it's not your scope but your target, as it is unlikely for both the tracking and reticle to be in error the exact same amount. If you hit right on, with a 4.2 MIL hold, then your scope may not be tracking correctly.

Either that or you need the services of an exorcist, not a scope repairman.

Regards,

Bob

 

[Garvey]

Re: OK big diff from calculator and actual dope?

I need to compare dope at the closer ranges. My target is 600 yards. That's verified by two seperate lasers. I could measure it with a wheel but I would think two lasers would be more accurate than a wheel going up and down across a plowed field.

I will try it with a reticle hold next time, makes sense to me to try that out.

 

[gstaylorg]

Re: OK big diff from calculator and actual dope?

How good is the # for your scope height above the bore? An error there can get you off in closer, but it will come back at slightly longer distance before going off again. It would have to be pretty far off though, so probably unlikely...just a thought.

 

[Garvey]

Re: OK big diff from calculator and actual dope?

I checked that in the calculator. I changed the scope height to many different numbers and couldn't make it calculate the actual dope in the field. This is puzzling.