Ballistics Question

[mallardsx2]

So say a guy has a rifle.

He sights in the rifle for 100 yard -0

He then checks the box and every ballistics calculator known to man and it says there should be a 2.5" drop at 200 yards.

He shoots the gun

It hits 6" low.

For the sake of argument lets say the grouping is Sub-MOA.

Also lets assume that the rings and bases are tight and properly set up.

Where does he go from there?

What could be causing this?

Need experienced shooters opinions.

 

[Gator89]

Factory ammo or reloads?

 

[mallardsx2]

Factory ammo.

300 WSM

Winchester 150gr silvertips.

 

[furtaker]

You're not getting the velocity the box says you're getting. I've had factory ammo clock 200fps under published velocity.

 

[mallardsx2]

But would 200 FPS equate to a 4" increase in drop? Seems excessive?

 

[spurrs and racks]

Try the 200 yard zero. It will shoot high at 100 but it won't be 6".

300wsm should perform at these distances +/- 1.5 straight up 12 - 6 oclock.


I also like Federal factory ammo performance over almost all ammo.

good luck

s&r

 

[Rich Kaminski]

I shoot a 300 Win Mag not the WSM and when zeroed at 100 yards I have a 3" drop at 200 yards shooting the same bullet as you with 180 gr.

 

[Philbow]

1 - Very low scope.
2 - Carbine barrel = lower velocity than factory test barrel.
3 - Just a plain slow rifle.
4 - Changing rest/shooting procedure from 100 to 200 yards.
5 - Something else
6 - All the above = cumulative effect

 

[mallardsx2]

1-1.5" high scope.
2-regular A-bolt II barrell
3-Dont know what this means.
4- sand bagged
5- maybe
6-maybe

 

[Lilly001]

Factory velocities are often taken from a 24" barrel. Sometimes 26".
If your barrel is shorter you will loose some velocity.
Each rifle, even from the same assembly line, will be different.
But my guess would be you are shooting a shorter barrel and loosing velocity to that.
But 6" is still a lot.

 

[JackSprat]

Rifle bore and both targets not in the same plane.

 

[jmoser]

Only an extreme difference in velocity [like 500 fps] vs expected could cause an extra 3.5" difference in drop. Bbl length is not the issue here.

Have you tried zeroing at 200 and checking the POI at 100? The way you hold and angle the gun can cause POI to jump, especially if you press your cheek hard on the comb. Be sure to use a consistent hold including cheek and shoulder pressure points. I get shots jumping high at 200M if I press harder on the comb. If the targets are much higher at 200 [or your 200Y shooting position is on lower ground for a fixed target etc.] the shooting angle can affect your hold if the bore has to be angled up. I am not talking about ballistic correction for angle of the shot - just the mechanics of how you hold and support the rifle.

I also wonder if this a parallax issue - rest the rifle on bags and look at the 200 yard target thru scope. Without touching the gun try moving your eye from edge to edge of the scope eyepiece, see how far the crosshairs move on the target. Parallax works in both axis - not just horizontal. If you can see the crosshairs move a few inches on the target you may have found your problem. Practice keeping your eye centered in the scope if you don't have a scope with AO or side focus feature. Again this can be result of how you hold and support the rifle.

 

[munchie3409]

There can be a lot of variables that change impact your POI vs what the factory says.

Only true way is to use a chronograph and record the temp/humidity and muzzle velocity you are getting with your rifle. Once you have that information, you can plug it into a ballistics program and it will give you accurate information for your rifle/ammo combo.

If you don't have a chronograph, see if someone on this forum can loan one to you or meet them at a range.

 

[mallardsx2]

Rifle is shot at 100 yards on 12X on a horizontal plane on sandbags off of a Granite Bench.

Rifle is shot at 200 yards on 12X on a horizontal plane on sandbags off of a Granite Bench.

Dead on at 100.

~6" low at 200.

Sub-MOA Grouping.

Same position shooting

Same Hold on rifle

Shooting through a Chronograph tonight.

Thanks for everyone's thoughts.

They are appreciated.

 

[mallardsx2]

I have not tried 0'ing the rifle at 200 yards yet.

 

[rayjay]

It would also be interesting to have the bbl looked at with a bore scope although the tight groups would make you think it can't be too bad.

 

[notnksnemor]

Until you find out and duplicate the exact conditions, especially elevation, the ballistics on the box were gathered at, you'll never know.
Elevation and humidity can have a huge impact.

 

[wareagle700]

How many shots per group and how many groups?

Possible parallax error in scope?

 

[mallardsx2]

Georgia. Hot day.

Elevation 800'?

3 shot groups. Sub-MOA.

 

[Jester896]

all of that can effect trajectory..
Hot Ga day... test barrel inside at 59 degrees
GA humidity 80%...test area 50%
altitude 800'...test area sea level
never mind barometric pressure
your barrel 22 " ...test barrel 26"

wouldn't take be a minute to get close to the 500 fps change

I would record the DOPE your rifle gave you and carry on as long as the conditions were the same....who cares what the box says when you have the info you need in front of you.