What would cause this? Bullet drop with elevation change

[7mmTikkaShooter]

I've always thought the case was a sealed environment?

I would guess the level of sealed environment will vary from case to case and from several obvious factors. If however, a round was loaded and sealed well enough then I could imagine the difference between inside case and outside air pressures having some effect on burn rate. As far as the lack of oxygen goes however; as I understand it, gunpowder propellants are considered oxidizers meaning that they provide their own oxygen for combustion and would ignite within a vacuum. Think of rocket fuel in space. Given the original scenario at hand I'm leaning toward something else being the cause. I gotta say this thread has gone down some rabbit holes! So many theories but I'm kinda feeling like this one might remain a mystery. Been fun to read though.

 

[sea2summit]

Verify your humidity theory before you post stuff like this! I just run a profile for one of my guns at 1500 yards. There is a 0.2" difference when comparing 0% vs 100% humidity at 1500 yards. Or 0.01" at 100 yards.

Easy there big fella. No idea what your shooting or what calculator so there's too many variables there. Why don't you verify your theories or post your references.

After seeing all the reports from the OP I think this has a lot more to do with a borrowed rifle than anything else.

ETA here are two different rounds going from 0 to 100%. Notice one has an almost uncorrctable amount of change, one has half a mill and that's at 1k and assumes the rifle was re-zeroed at 100m every time because I didn't want to change that much data.

 

[wbm]

His rifle zero has changed since you sighted it in, or he shoots the rifle to a different POI than you

.

 

[wkdwdg66]

Doesn't sound right at all does it? I was hoping Litz had an easy read on the internet I could find but no luck, here's another reference.

Ballistic Effects of Altitude, Temperature, and Humidity - Lilja

At a match recently I overheard another competitor comment that the wind seemed to be blowing the bullets more than usual that day. He suggested that the humidity level must be high, that the air was “heavy”. I know that there have been days when it seemed to me that a little change in the...

riflebarrels.com

I have his book, I should probably just get past the first chapter and figure some of this stuff out. I've been "faking it" as a long distance shooter by using really flat shooting cartridges. Time to actually get in the game, eh?

 

[sea2summit]

I have his book, I should probably just get past the first chapter and figure some of this stuff out. I've been "faking it" as a long distance shooter by using really flat shooting cartridges. Time to actually get in the game, eh?

All his books are on the Kindle subscription. I binge read them last deployment and there's a lot of repeated information but I still don't have it all down. Dude has a huge brain.

 

[wkdwdg66]

All his books are on the Kindle subscription. I binge read them last deployment and there's a lot of repeated information but I still don't have it all down. Dude has a huge brain.

I haven't been on deployment since '13. Definitely enjoyed reading during down time. I try to set time aside, but #life.

 

[Pdvdh]

117 posts later...

"His rifle zero has changed since you sighted it in, or he shoots the rifle to a different POI than you."

But multiple UFOs has more pizzazz.

 

[mtwarych]

I have the understanding to use pressure as absolute. I have yet to dial for elevation.