Rifle shooting high consistently with drop chart
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Canadian Bushman
Well-Known Member
I have not experienced this
I believe this is correct. The end effect of the 20 MOA rail is to raise the end of the barrel by 20 MOA. The scope would then remain horizontal and the turrets would track just the same as if there were no 20 MOA rail.
Canadian Bushman
Well-Known Member
The erector tube is zeroed in the same place regardless of the scopes body, which is canted to move the erector tube closer to one end of adjustment. At the extreme ends of adjustment you risk the scope not tracking a true moa because the steep angle of the erector tube ( a couple degrees ). This effect is usually unnoticed, often exaggerated, and easily tested.
This could potentially blur the true measurement of the scopes centerline to the bores centerline but only by very small numbers that are not relevant to the op's post and often lost in the noise on much longer firing solutions.
I.E. - A change in .125 ( aprox 120moa on a 4" erector tube) to scope height on a 2000 yd shot is .1 moa difference in traj. Ive never shot within .1 moa at that distance.
If you measure to the center of the scope body you effectively cut this error in half.
I've used the Vortex ballistic calculator and used the trajectory validation on it. BC values change with velocity and published BC's are averaged for a given speed range. Take those numbers you gave and put them into the Vortex calculator and see what it says.
Also compare it with the Berger ballistic calculator
Also compare it with the Berger ballistic calculator
bigngreen
Well-Known Member
Not an issue, we dial in rifle with 20 moa all the time and regularly 45-65 moa rails with no issues!!
stomp442
Well-Known Member
Easy solution. Shoot your rifle at known distances and record those numbers. Make a chart of your own and get to work. I don't care what an app says I want to know exactly what my rifle is doing and what I need to dial to, to make hits at any given range. An app is a poor substitute for actual shot drop data. They may get you close but rarely centered up. With the amount of ammo wasted already you could have an accurate drop chart of actual drops made for every 50 yards out to 1000.
WildRose
Well-Known Member
You've gotten a lot of good advice on this thread already but I have an idea for you to try.
Take a target and mark four one inch bull's, one in each corner (with several inches to spare) spaced 12" apart so they form the corners of a perfect square.
Use your top right bull for the aim point for each of the shots fired.
Start with your top right bull and fire a shot. Dial your scope 12 MOA down and fire another. Your impact should be in the lower right bull.
Dial 12 MOA left, fire a shot. Your impact should be in the lower left bull.
Dial 12 MOA up and fire. Your impact should be in the top left bull.
Finally dial 12 MOA back to the right and fire. Your impact should be back in the original top right bull.
I'm starting to think your whole problem could be the scope.
I had several Vortex Viper PST's that didn't track consistently up and down.
If that's your problem you could waste a lot of time, money, and frustration chasing all the other possible causes and four shots is cheap insurance for peace of mind.
If that's not your problem as others are suggesting the most likely cause is a velocity problem either with your loads, or inputs or a combination of both.
We've all had hard to nail down problems at one time or another so you're in good company here! gun)
MOA bases absolutely can have an impact on this situation. Its just geometry and it is real. If you measure scope height in wrong place it will drew up your ballistic program. To prove this measure your scope height at the back of the scope and front of the scope. You will get a different measurement. However if you measure scope height where the crosshairs are the 20 MOA base will not matter.
Also the wrong scope height can have a pretty significant effect on downrange impact.
Another issue can come into play if the 200 yard zero is really "zero". If you are slightly high at 200 yards this will carry through there rest of the yardage. In other words 1\4 MOA high at 200 or worse yet 1/2 MOA, wild change the ballistic curve completely. It is important to put the exact zero into your program.
bigngreen
Well-Known Member
My 338 will see a 1.4 inch difference at 800 yards due to being a whole half inch of on my scope height. If you measure near the turret with even a crude tool you'll be more than fine to the ranges the OP is running and it's not his issue.
Zero IS a very critical item and one a guy needs to prove by shooting at 100 then at 300 yards with a reasonably close velocity, I tune my zero before going to long ranges which I usually do at 1000 yards where a minor velocity change will be looked at if needed. Using a quality G7 BC from Litz there is no need to tune the BC till you get near transonic and then only maybe.
WildRose
Well-Known Member
When I first started using ballistic programs I learned very quickly just playing around with the scope height proved it to be a very minor factor compared to the rest.
Assuming your set up is right and you have a load that performs consistently for velocity and the bullet is stable nothing I have found gives as much variation as not having a true "zero" to base the calculations off of.
Even without a chrony and a true known velocity you can easily come up with the right velocity by doing as you say and verifying your drops.
Get a true zero and two measured drops more than 100yds apart and your calculations out to 1000yds are going to be very accurate.
WildRose............ I'm starting to think your whole problem could be the scope. I had several Vortex Viper PST's that didn't track consistently up and down. If that's your problem you could waste a lot of time said:
Ok I'm not trying to argue with you just trying to stay with the facts. Let me start by saying I do not own a .338 so my comment is limited to my own experience. I ran a ballistic program on 2 of my rifles this morning and changed the scope height 1/4 of an inch. I saw a change 1/2 MOA on 1 and 1/4 MOA on the other, both at 700 yards. That is approx 3.5" or 1.75" respectively. For the record the rile that of 1/4 MOA has a much flatter ballistic curve than any .338 that I know of. So because I am assuming that the issues we are talking about in this thread are possibly a combination of causes I do not think that discounting scope height is a good idea. I know for me that if my program was off by 2-3 inches at 700 I would want to correct that. Also ASSUMING, that you are 2" high because of wrong scope height input and an error in zero at 200 I could easily see being off target by a full MOA or even more.
But 1 thing for sure is an incorrect scope height will make a difference which was my statement in the first place.
