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.

 

[MThuntr]

he ignores the box...and shoots at all distances he plans to hunt for known impacts.

 

[Deleted member 28227]

Slower than advertised factory ammo, shorter barrel on your rifle ie 22 inch barrel on your rifle v. 26 inch barrel on the rifle they used to calculate the stats? Shooting it through a chronograph would be my first step.

 

[Mallardsx2]

Both valid points so far.

 

[Mallardsx2]

Although, even if the velocity was dropped by 100 FPS it would not accumulate that significant of a difference from 100 to 200 yards.

 

[Bigjay73]

Try different ammo

 

[N2TRKYS]

To many assumptions in this for me. Sight it in at 200 yards and check poi at normal hunting distances.

 

[VikingsGuy]

If you don't check the actual velocity out of your particular barrel the calculators are less useful (but I am surprised at -3.5" off at 200y). You can drop 100-150fps due to shorter barrel. Actual chamber size of your gun can affect actual velocity a little, as can seating depth, and temperature. Rifle/scope cant can also start affecting POI as you stretch out your shots. Also, some manufactures overstate their BCs. In the aggregate I am guessing this could cause some of what you are seeing.

 

[Bigjay73]

What caliber and gr are you shooting?

 

[BucksnDucks]

Going off the limited info given I would look at point of aim/parallax scope issues first. Shoot at 50 then 100, 150, 200 I don't have an explanation for 6" drop at 200 yards unless you are shooting a very low velocity heavy bullet combination. I suspect a "mechanical" issue with scope set up before a ballistics problem.

 

[Mallardsx2]

300 WSM 150 Gr silvertips.

 

[Bigjay73]

That's definitely not a slow heavy round.

 

[Mallardsx2]

No. It leaves at 3300. I'm going to chronograph tonight. But I dont think that is going to p[rove anything significant.

 

[VikingsGuy]

No. It leaves at 3300. I'm going to chronograph tonight. But I dont think that is going to p[rove anything significant.

If it’s going over 3000 FPS then it is most likely scope cant/parallax issue. It’s not really dropping 6” from true point of aim, rather you likely have an incorrect point of aim vs point of impact.

 

[belly-deep]

Was the height of the scope above the bore estimated? Or actually measured?

 

[jryoung]

300 WSM 150 Gr silvertips.

I'd look at shooting something other than winchester ammo. I've put it in three different sub moa guns and if I didn't know better I would have thought about selling the gun.

 

[Mallardsx2]

Was the height of the scope above the bore estimated? Or actually measured?

This is estimated.

 

[Mallardsx2]

I would think a rifle cant would throw the bullet wide? Its hitting at the 6:00 position ~6" low.

 

[Mallardsx2]

I'd look at shooting something other than winchester ammo. I've put it in three different sub moa guns and if I didn't know better I would have thought about selling the gun.

I have had good luck with this ammo grouping. Hence the reason I never switched. I will try another brand of ammo and see what happens.

 

[VikingsGuy]

I would think a rifle cant would throw the bullet wide? Its hitting at the 6:00 position ~6" low.

I was being sloppy, you are right pure cant moves poi horizontally. I said cant/parallax as a poorly chosen place holder for screwed up scope alignment in general - that it is not that the bullet is dropping at a dramatically faster rate, but that something in your scope setup is causing you to aim the barrel much lower at 200y than you did at 100y.