What would cause this? Bullet drop with elevation change

[JMW67]

outfitter screwing with them

 

[TheLongRanger83702]

What does wormhole mean?

Sounds like a personal insult to me so it can't be good.

 

[TheLongRanger83702]

Just to clear a few things up. There was no flight involved. The odds of 6 rifles all being messed with in in transport in there own trucks is basically impossible. There is another factor coming into play here, I'm just trying to learn something.

Generally speaking the higher in elevation the flatter the trajectory. However if you sighted in at a dryer climate but are hunting in high humidity that could offset that elevation effect with a slower bullet flying through denser air. Temperature could be an additional factor. Your MV at 80 degrees will be faster than that same powder charge at 30 degrees. Ive read some guys keep their ammunition in a protected pocket from the cold and load only when ready to shoot so the round isnt effected by heat OR COLD temperatyres.

 

[emp1953]

I mounted a scope and developed a load for a friend of mine. I'm at 850 feet of elevation. The gun was shooting great when he left. I had it zeroed at 100 yards. He got to his elk hunt today. He is 2 inches low at 100 yards and is at 7200 feet. He dialed the correct moa and tried at 350. He his 6 inches low. He's the clinker, there are 6 guys on this trip and everyone of them is seeing the same thing. Higher elevation shot be less bullet drop but not in this case. The gun is a tikka 300 win mag, h1000 powder, 200 gr eld-x. Temps are similar to when we shot here. Anyone have any ideas?

2" at 100 yards is too large of a change for the elevation change, yes the air is thinner, probably the humidity is higher, probably the temperature is lower, etc etc. Go to a good ballistics calculator, dial in all the criteria and the bullet drop for the elevation that was originally shot and the 7200 feet. you'll find the difference is minimal. 2" suggests other forces at play. Different shooter, loose scope, rough handling, cheap scope? I had a horse slip and fall on rocks, falling on the scabbard carrying my scoped Cooper custom rifle with a synthetic stock. I had a really good Nikon Monarch scope on it. A quick test showed that the zero had not changed at all. Did all the hunters fly into the site? Airlines are notorious for rough handling of firearms. I had one not show up at all one time.

 

[emp1953]

Generally speaking the higher in elevation the flatter the trajectory. However if you sighted in at a dryer climate but are hunting in high humidity that could offset that elevation effect with a slower bullet flying through denser air.

The factors that you mention will have a tendancy to offset each other. More humidity will to some extent be offset by thinner air or higher temperatures, uphill and downhill has a lot of effect as well. Yes they can all combine in the same direction in some instances, but not for 2" at 100yds.

 

[kbrent1223]

Just throwing this out there. I've read all the reply's on temp. So certainly worth looking into. Different rest, could be. But I would throw out that powder will burn at different rate at 860 ft vs 7200. Especially if cold. So much less Oxygen at 7200. Rate of burn slows and velocity falls off slightly. Cold temp and less O2 to fuel the burn equals slower velocity in any textbook I've ever read.

 

[RuninL8]

So there are only a few explanations for this happening. Physics will not allow a bullet to have more drop at a higher altitude than a lower on. So take that off the table. Are you reloading, did you change lots on powder? Are you using factory ammo and opened a new box, that could have different velocity. The next thing is was there an actually trajectory validation done with the ammo and rifle with the shooter that would hunt with the rifle, if not, thats your issue. The next thing is did the scope come off 0/0, do you have exposed turrets, did they get turned in the truck. (ITS HAPPEND TO ME) Are you sure everything is tight and not over tight. The other thing would be the crown of the rifle, if it got dinged or changed in any way, and believe it doesn't have to be much, that could be your issue. Hope this helps.

 

[HANGum HIGH]

With out a doubt, it was president Trump! He is the cause of every issue Americans have!!!

 

[checkursix]

I guess there's no chronometer available?

 

[J-B welder]

So much less Oxygen at 7200. Rate of burn slows and velocity falls off slightly. Cold temp and less O2 to fuel the burn equals slower velocity in any textbook I've ever read.

I'm brandy new to reloading, but I thought powder didn't need oxygen. From the Lyman manual: "[Smokeless powders] are designed to burn rapidly and to do so without the presence of oxygen - generating all required oxygen as they burn." Seems like O2 level shouldn't be a factor.

Not trying to be a smart-***. Being new, I'm actually wondering if I'm misunderstanding something.

 

[TheLongRanger83702]

I'm brandy new to reloading, but I thought powder didn't need oxygen. From the Lyman manual: "[Smokeless powders] are designed to burn rapidly and to do so without the presence of oxygen - generating all required oxygen as they burn." Seems like O2 level shouldn't be a factor.

Not trying to be a smart-***. Being new, I'm actually wondering if I'm misunderstanding something.

Agreed. How could ANY change in oxygen levels around the rifle, sneak down the bore... get past the seated bullet still in the cartridge and in where the powder is, mixing together waiting for ignition. Thats a new one.

 

[Scott E Ames]

I know this sounds basic but did anyone at the shooting bench double check the range of the target with a range finder? It could be 50 or 75 yards further off if it is across the valley and that might account for some of the low impact points.

 

[emp1953]

So there are only a few explanations for this happening. Physics will not allow a bullet to have more drop at a higher altitude than a lower on. So take that off the table. Are you reloading, did you change lots on powder? Are you using factory ammo and opened a new box, that could have different velocity. The next thing is was there an actually trajectory validation done with the ammo and rifle with the shooter that would hunt with the rifle, if not, thats your issue. The next thing is did the scope come off 0/0, do you have exposed turrets, did they get turned in the truck. (ITS HAPPEND TO ME) Are you sure everything is tight and not over tight. The other thing would be the crown of the rifle, if it got dinged or changed in any way, and believe it doesn't have to be much, that could be your issue. Hope this helps.

These are definitely factors that could contribute to the change. Some powders are extremely sensitive to temperature extremes, which would change velocity up or down, changing the POI, some are more sensitive to air pressure changes as well, some suffer from both of these sensitivities. I made a change from I4350 in a .270win to H4350. The POI was off both in windage and elevation, An inch low in elevation and 1" right in windage. I was not expecting the Hodgdon powder to perform just like the IMR version. Reloading manuals suggested similar velocities for the same load. 150fps apparently makes that much difference on the target at sea level. When I chronographed the Hodgdon loads the difference was less than the manuals but still was consistently different. I found that marking the primers of the Hodgdon loads with a Sharpie, when using them I could dope my scope back to a correct POI. You have to have a scope that tracks reliably to do this though.

 

[Pdvdh]

Wormhole.......

This is by far and away, as good a possible cause as any.
I wouldn't waste any more time on it, searching for other reasons.