Anyone had this problem

[daspurlock]

Went to the range yesterday was shooting my ar, started at 100 yrds everything was fine, moved to 200 everything good there. When I moved to 300 ( I use a nikon w/bdc) the bullet droped about 10 inches from normal holding point which is first dot under crosshair. Had to move my aiming point to the second dot. Ammo was once fired 55gr fmj from usa ammo, I've never had any issues with their ammo before but I' never had this happen before and that was the only ammo I had with me. Anyone who has any thoughts on this I would really like to hear them.

 

[netsecurity]

That's exactly what is supposed to happen . For a human sized target, you aim for the head at 300yds, and you will hit center mass. Ten inches is right on normal for 223/556. After 300yds the bullet drop is significant in an AR-15, but since most engagements (before Afghanistan) in war are under 300 yards, then it matters little. Even though the maximum effective range of 556 is supposed to be 600m, shots at that range are more suited for 7.62/30 cal.

BDC is just a guide. I'd document your hold over.

 

[daspurlock]

May not have been very clear scope was already sighted in. Had shoot targets at this distence many times before using first dot for aiming point hitting target right where I was holding. but not this time only thing that had changed was aiming point at 300 yrds.

 

[Mr Evilwrench]

That's how it works. You zero at whatever range, it'll hit high at shorter range and low at longer. If you have a scope that's calibrated for your round, it'll have lines for longer ranges which are below the zero line. I don't know what you think you've seen before, but when you fire beyond your zero range, it'll be lower and you have to compensate. The bullet starts dropping as soon as it exits the muzzle.

 

[Armed-N-Ready]

Gravity happens.

From the time it leave the muzzle.

 

[ATM]

...I don't know what you think you've seen before, but when you fire beyond your zero range, it'll be lower and you have to compensate.

By my reading of the OP, it seems that what he saw before was rounds hitting where they should when he held high to that lower dot (compensating correctly for the further distance.) This new batch of ammo is dropping 10 inches lower than the last batch did at this same distance.

Maybe got a weak batch or comparing completely different loadings.

That's how it works. You zero at whatever range, it'll hit high at shorter range and low at longer.

...The bullet starts dropping as soon as it exits the muzzle.

No, that's actually not how it works.

 

[Drakkule]

Remember that the colder the air, the more dense it becomes also.

 

[daspurlock]

Thank You someone finally got what I was saying. I was thinking that I got a bad batch. Will the cooler air make it shoot lower?

 

[Mr Evilwrench]

No, that's actually not how it works.

Huh? It does so! Ok, maybe I read the op differently than he wrote it, but that's a different issue.

 

[patience0830]

Thank You someone finally got what I was saying. I was thinking that I got a bad batch. Will the cooler air make it shoot lower?

It shouldn't make it shoot 10 inches lower. Sounds like a different recipe.. But depending on what powder they used to load the rounds, temperature can make a difference. Last I heard, Varget was the least temp sensitive powder available to handloaders. Hence, the most consistent.

 

[2tonic]

How did the temperature on this range trip compare to your previous experiences? Similar temps, or was this trip colder?
Cold can affect ignition, cyclic rate, and vision among other things. More important is its' effect on air density and the friction influencing a bullet in flight.
This is where I would look first to explain the phenomenon you described. Then look to the ammo .....different lot number, short powder charge, incorrect OAL (bullet seating), case neck tension, bullet shape....any and all have an effect.
Try some other ammo to compare drop at range "X".

Gravity is a constant, everything else is variable.

Oh, by the way, the bullet starts dropping below the line of the bore as soon as it exits the muzzle, but since the bore is angled up the bullet traces a double-decaying bi-variate arc through the air.

 

[ATM]

Huh? It does so! Ok, maybe I read the op differently than he wrote it, but that's a different issue.

If you zero a centerfire at at 25 yards, your impact will be higher at 50 and even higher than that at 100. At further distances it will begin to drop back to your original zero and below. Your sighting system point of aim may be a flat line, but your barrel is not pointing there and the bullet does not travel in a flat line.

...Oh, by the way, the bullet starts dropping below the line of the bore as soon as it exits the muzzle, but since the bore is angled up the bullet traces a double-decaying bi-variate arc through the air.

Or you could get technical...

 

[Mr Evilwrench]

I understand the barrel doesn't aim where the scope does. The scope directs your barrel off level to hit the aim point. However, the bullet starts to drop immediately upon its exit from the barrel. There is no disputing this. Gravity has its effect as soon as the bullet is no longer supported by the barrel. There is an additional factor in the zeroing, which is the vertical offset of the sighting system from the bore. This will introduce an error as you have noted, where there will be two apparent zeros, but understand that is due to an error; it's not really a feature, it's a bug. The exact offset, the ballistic characteristics of the round, the load, will all affect the zeros; they're not really as predictable as all that. They could all theoretically be calculated to precise values given measurements, but it's still a bug from the vertical offset.

 

[IndianaGTI]

Cooler air will cause bullet drop and humidity will also cause bullet drop.

Rain will cause more bullet drop. At one appleseed, I had to adjust mid-aqt to shoot 1" higher at 25 yards with a .22 that shot only 1000 fps because of rain. Literally, 1" higher at 25 yards.

 

[ATM]

Mr. E, Your earlier references of drop would not apply to the targets or zeros as if the gravity were causing the bullet to drop with reference to the sighted plane.
Just busting on what I saw stated as an illogical inference, even though you do seem to know better.

All in good sport.

 

[Mr Evilwrench]

Sorry, I'm an inveterate engineer, and use science to explain what I see. Gravity pulls on everything, and if nothing is supporting it, it falls. If you aim something, the only way it will hit your aim point is either by aiming on axis, or cheating. You can't aim on axis, so you cheat, and there are results. One of those is the phenomenon of two zeros. Don't be misled. It's all because your scope is so far above your boreline. It's not because you're doing something wrong; you're doing the best you can. You're just limited by technology. The real measure is in how many deer or bad guys or whatever fall down when you shoot at them.

 

[sloughfoot]

16 inch or 20 inch barrel? It really matters. A lot.

 

[superjoe76]

Cold ammo is also under less pressure than hot ammo so it may not be getting the full ummf out of the barrel.

 

[DoggyDaddy]

I know that what has been stated here (bullet begins to drop immediately due to gravity) is true in a vacuum, but wouldn't air resistance also come into play? In other words, the aerodynamic properties of the projectile providing lift or drop? I'm not an engineer... just thinking back to high school physics class...