Elevation, MOA, Air Pressure POI, WTF

[peacefrog]

Does this happen to anyone else? I know there are variables and differences between ballistics programs, I was at the range today and plugged in my variables into iSnipe to get some dope. I was shooting at 300 yards, and iSnipe gave me an elevation to dial in of 2.8 MOA. In reality, I needed 4.5 MOA on the scope to hit centre of target today. This is not the only instance of iSnipe being off, or different than reality. My first shots with 2.8 MOA on the scope hit about 5-6" low, centred but low. When I dialed up to 4.5 MOA it was dead on centre 3 shots that could be covered with a .75" patch, very little wind today, sunny about 8 Celsius.

Earlier this year, I was running at most 3.5 MOA to 300, and one day in July, only 1.5 MOA was required.

Nothing with my load has changed. 39.2 gr of Varget pushing a 129 gr VLD out of a 30" match barrel chambered in .260 Remington. My velocities today were in line exactly with earlier data and I'm averaging 2906 fps.

If I understand correctly Varget is supposed to be temp stable, no?

So is it air pressure, temperature?? I'm lost now. I keep everything as consistent as possible and try to make perfect shots every time I pull the trigger. Everything is tight (scopes, bases, rings, action screws). So looking for some wisdom here. Thanks.

 

[ultimate_monkey]

cool temps = denser air = more drag on bullet = more MOA needed,

yes varg is temp stable, but once that bullet leaves the barrel, it pretty much all has to do with air density

 

[peacefrog]

cool temps = denser air = more drag on bullet = more MOA needed,

yes varg is temp stable, but once that bullet leaves the barrel, it pretty much all has to do with air density

So if it's all about air density is there a way to get more accurate data, without shooting a billion rounds under every conceivable temp/humidity condition and making a massive trajectory chart?

 

[ultimate_monkey]

youd need somthing like a kestril that can give you the elevation, temp and pressure, and then enter that into isnipe daily variables and it shoud get you alot closer. the down side is that air pressure and air density are 2 different things, and u cant adjust both... one other thing with isnipe is that there is no proper way to correct the algerithom, so it will never be 100% on, just very very very close

 

[maynard]

If you dialed up 4.5 MOA at 300 yards would that not move POI up approx 13.5 inches?

 

[Boomer]

youd need somthing like a kestril that can give you the elevation, temp and pressure, and then enter that into isnipe daily variables and it shoud get you alot closer. the down side is that air pressure and air density are 2 different things, and u cant adjust both... one other thing with isnipe is that there is no proper way to correct the algerithom, so it will never be 100% on, just very very very close

A Kestrel 4500 with the A-Trag ballistic program. I'm borrowing one right now, and its pretty cool. At extended ranges, with my rifle data plugged in, the firing solution changes constantly (in tenths of mils) as the Kestral senses differences in pressure and wind speed. My only complaint thus far is that the screen is a bit small.

 

[caramel]

The old fashioned way is still very actual... JP.

 

[Chinbullco]

Guys, this is progress? Now you're using your rifles to prove your instruments.

 

[caramel]

Shooting is a trial and error thing, with all your sophisticated stuff, you guy could actually shoot at the moon and... hit it... JP.

 

[peacefrog]

If you dialed up 4.5 MOA at 300 yards would that not move POI up approx 13.5 inches?

Sorry Maynard, I meant I had a total of 4.5 MOA on the scope. So I went from 2.8 (2.75 MOA on the dial) up to 4.5 MOA (added 1.75). My scope is zeroed is at 100 yards.

 

[peacefrog]

youd need somthing like a kestril that can give you the elevation, temp and pressure, and then enter that into isnipe daily variables and it shoud get you alot closer. the down side is that air pressure and air density are 2 different things, and u cant adjust both... one other thing with isnipe is that there is no proper way to correct the algerithom, so it will never be 100% on, just very very very close

I agree UM. I picked up a Kestrel 2500NV late summer, (didn't have it yesterday, DOH), however even with the daily variables, I still get that 2.8 MOA setting from iSnipe. It would be nice if a user could plug in actual range results and have iSnipe correct on those actual real life numbers. I wonder if it would be more accurate overall.

 

[ultimate_monkey]

Of course it would be more accurate , ballistic calcs are only predictive, they will only ever be as accurate as the data imputed . When you can't enter vital data like air density your predictive curve will be off , same with not being able to true the algorithm to match true range results

 

[caramel]

Mr. Spock would have said... Fascinating... JP.

 

[ultimate_monkey]

...Wow... JP.

Well we don't all have a fortune to spend on factory ammo to shoot "trial and error". Hahah I kid!

But really if I can get on target in 3 shots using a calc rather then 10 taking guesses I'd much rather be practicing my marksmanship with those extra 7 shots then dialing my scope

 

[caramel]

Well we don't all have a fortune to spend on factory ammo to shoot "trial and error". Hahah I kid!

But really if I can get on target in 3 shots using a calc rather then 10 taking guesses I'd much rather be practicing my marksmanship with those extra 7 shots then dialing my scope

I really am old school in shooting but this is real interresting... JP.

 

[peacefrog]

Well we don't all have a fortune to spend on factory ammo to shoot "trial and error". Hahah I kid!

But really if I can get on target in 3 shots using a calc rather then 10 taking guesses I'd much rather be practicing my marksmanship with those extra 7 shots then dialing my scope

I will have to keep more detailed notes regarding actual range results and weather conditions, so I can set my sights to the "best" starting point for the day.
Thanks for the feedback.

 

[Mystic Precision]

What type of scope?

What type of rifle? more importantly - what type of stock?

What type of restsf? Same location for all shooting?

There are definitely changes elevation due to ambient condition changes but at 300m, that seems alot.

Jerry

 

[b72471]

I can see I'm getting left in the dust by the younger generation, i Snipe, Kestril4500 & Logarithoms, I'm going to have to read up on these systems.
I'm still using the "GREEN MASKING TAPE" system. Yup, once you have found your scope setting for 100 out to 1000, write them down on the green masking tape on the side of your stock, make sure to write it upside down so you can read at a glance, like the Swedes did with their stock disc on the butt stock of their 96 mausers.
Now to look up this i SNipe.

 

[Jeromeo]

Shooting is a trial and error thing, with all your sophisticated stuff, you guy could actually shoot at the moon and... hit it... JP.

Only with a Nemesis. All other rifles are inferior, right Caramel?

 

[rnbra-shooter]

At only 300 yards, a whole lot of factors matter very little if at all - among these "don't matters" are air temperature, barometic pressure, humidity, rifle cant, ammo/powder temperature, wind speed and angle, batch of bullet, lot of powder, brand of primer, loose bedding screws, etc.

If you needed 3.5 MOA (up from 100y) all summer long, but 4.5MOA recently, that is a *big* change, one that is unexpected and not easily explained. And if one day in July you only needed +1.5 MOA to go from 100y to 300y, that's a ridiculous outlier that sounds alarm bells. There is something wrong in your setup somewhere, something that would be worth while discovering and fixing.

From one shooting session to the next, it's completely reasonable to see your 300 elevation differ by a quarter minute from your usual setting; click it in if it needs it and don't even spare it a second's thought. It's even within the realm of reasonableness to see a half-minute different in your elevation setting from your long term average, but any more than that I would declare that there is something wrong somewhere, which needs to be found and fixed.

The prime culprit is always the scope, if you are using one (or its mounting system). Start by verifying that the rings and bases are tight. If you have a collimator (optical boresighter), put that on, click your scope around, and see if the scope's internals move as they should - cleanly, without backlash or hesitation, in consistent and proper amounts. If you don't have a collimator but if you do have another known good scope that you can put on your rifle, do that and see how things work with another scope.