Rifle shooting high consistently with drop chart

[Kelpy]

So, when dialing a scope I have realized that my rifle shoots consistently high at yardages 400-1000. I know asking without any background information is only going to lead to speculation. But I need to know where to look for what is causing the difference between my ballistic calculator and point of impact.

Rifle: Tikka T3 300 win mag
Bullet: 215gr Hybrid VLD (.696 BC)
Scope: Vortex Viper 6-20
Harris Bipod

The gun is sighted in at 200 yards. 5800 feet elevation

I have run the numbers through two different ballistic calculators and there is not enough difference between them to be causing the difference in POI.

Things I don't know are: Is the published BC for this bullet correct? How do you measure the scope height?

Possible problems: I can't find my good chronograph and had to borrow a shooting chrony from a friend and maybe it isn't as accurate as I would like it to be. . .

Any suggestions? Thanks, Kelpy

 

[FEENIX]

How do you measure the scope height?

Pull the bolt out halfway and measure C/L of bolt and C/L of scope.

You also go to YouTube "How to measure scope height the easy way" by Sam Millard.

 

[smokeumm]

How high is your 400 and 1000 yard shots? Yes maybe the bullet's BC or speed is a little low. Scope height should be around 1.80 inch's for must setups. But at 400 yards if you're off 1/4 of an inch on scope height that wouldn't be much change, maybe a half of inch at best.

 

[Kelpy]

Ok, so it sounds like the scope height is not the problem.

At 755 this morning I was shooting nearly 2 feet high. . . I haven't shot at 1000 yet but at 500 I am about a foot high. These are just rough estimates from shooting rocks/clay pigeons. I need to take a big sheet of cardboard out tomorrow to get some better impact locations.

Thanks, Kelpy

 

[Kelpy]

I guess on another note.. . This rifle has less than 100 rounds down the tube. Is there a chance that velocity can increase as the rifle barrel breaks in? Could that cause the velocity that I am using to be low?

 

[Canadian Bushman]

More than likely its a combination of things.

#1 - incorrect reading from chronograph.

#2 - possible velocity error throwing off g1 bc - use g7

#3- accuracy of your zero

Just my guess.

On a side note ive found bergers bc on the 215 to be very accurate if properly stabilized.

Never hurts to double check the twist rate of your barrel.
Twist Rate Stability Calculator | Berger Bullets

 

[Kelpy]

Checked the twist rate and it lands at 1.49, so right on the comfortable/marginal stability line. I would think that should be good. Especially since I have been getting 1" groups at 200 yards. If stability was a problem it would seem that at close yardage my groups would not be so tight. . .

 

[smokeumm]

It's not uncommon to see an increase of 100-200 fps invelocity once your rifle brakes in (normally 75-150 rounds for complete brake in). Do not trust chronographs for perfect total speed, I use them for speed consistency during load development. To find perfect bullet speed, you will have to tweak speed up or down in your calculation, after you validated groupings. I'm guessing your zero is not perfect and your speed is not perfect. Check zero and bump speed up. Shot at 200, 300, 400, 500 and so on, that will give you have great picture of your bullet drop and how well your chart is. I have a hard time controlling the kick of my 7 stw. Try not to free shoot your rifle (by only touching the gun with you trigger hand). Put some downward pressure on the front of your sling so eliminate jump.

 

[bb204]

Just a thought here. Could you be calculating in MOA and your scope clicks be in Mils ? That is quite a difference in elevation for the velocity or BC to be off by that much. Again, just a thought.
Good Luck

 

[TimeOnTarget]

I'd just change the info in my Bal. Calc to match my real world experiences.

A foot at 500 yds is a big difference!

By chance, did you run them over the chrony, when it was cold out and now the air temp is hotter?

 

[Kelpy]

It states on the scope that the adjustment is in MOA.

 

[Kelpy]

It was actually warmer out (by 40 deg) when I shot them over the chrony. . . this would mean its backwards to what you would expect. But good thought none the less.

Anyway, I will try tweaking the velocity (because you have all suggested it and I don't trust the shooting chrony) and see what happens.

Thanks, Kelpy

 

[Canadian Bushman]

Checked the twist rate and it lands at 1.49, so right on the comfortable/marginal stability line. I would think that should be good. Especially since I have been getting 1" groups at 200 yards. If stability was a problem it would seem that at close yardage my groups would not be so tight. . .

I mean physically check the twist rate of the barrel with a cleaning rod to make sure it is what it says it is.

Groups dont always reflect stability. Ive shot very tight groups with marginally stable bullets, and do so regularly.

 

[EdWalton]

I'm reading Bryan Litz's book.
To measure the scope height he recommends:
Measure the diameter of the barrel then divide by two.
Measure the diameter of the scope then divide by two.
Measure the gap between them.
Total the three measurements.

He recommends you use calipers.

I don't know much, but I hope I can help you with his instructions.

Ed