Point of impact changes

[Bean Counter]

Anybody know if changing 3,000' in elevation is enough to knock off a whopping six minutes of angle to your zero? ... yeah: 24 clicks. 

[coachcw]

That's a ton !

[jasnt]

That's very extreme. What range are you zeroed. What preasure are you zeroed in and what was the difference in preasure?

[jasnt]

What caliber?

[Fl0und3rz]

Just running standard sample numbers at

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

for a 168 grn SMK at 3,000 fps, you only get about 0.4 MOA difference at 500 yards (that is, more drop at the lower elevation) and about 3 MOA difference at 1,000. 

I think you may have something bigger going on with the rifle than just an elevation (BP) change.

[Bean Counter]

.270 Winchester. And yes, same round and grain weight 

Not sure what you mean by 'pressure' 

[Bob33]

No.

Something else is causing that much shift.

[Bean Counter]

What range are you zeroed.

First range day I zeroed at 200 yards. Then I shot small steel targets from 300-550 yards all day long. Second range day I had to make some minor adjustments but was at least still on paper at 200 yards.

 

That's a ton !

Indeed. But I'm kind of glad it was so far off and not say 1.5 MOA with a hundred wounded lopes and deer across the Red Desert. I had lots of complete misses and it wasn't until I wounded a doe (and yes, we looked a LOT for her to finish her off) that I decided to finally blame the equipment rather than  buck fever and operator stupidity. Rezeroed and the bloodbath resumed.

[birddogdad]

No.

Something else is causing that much shift.

 

maybe 1 INCH of change (only for air) for a 10K foot elev change at 100yds... could be seen.. (all other variables equal)

[jaymark6655]

temperature difference and a really sensitive powder?  Maybe the swing in  chamber pressure is causing the bullet to leave the muzzle at a different point in its vibration or recoil?

Pressure changes with altitude, but temperature and humidity also change it so an increase in altitude of 3000 physical feet might be effectively a lot more if you sight in at sea level on a really cold day with no humidity and then climbed 3000 feet higher and shot on a really hot, humid day.  I can't imagine any change in weather that would cause that much of a shift though.

[CaNINE]

temperature difference and a really sensitive powder?  Maybe the swing in  chamber pressure is causing the bullet to leave the muzzle at a different point in its vibration or recoil?

Pressure changes with altitude, but temperature and humidity also change it so an increase in altitude of 3000 physical feet might be effectively a lot more if you sight in at sea level on a really cold day with no humidity and then climbed 3000 feet higher and shot on a really hot, humid day.  I can't imagine any change in weather that would cause that much of a shift though.

 

What powder are you using?  If you're not using a temp stable powder you could see that much shift.  What were the environmental conditions when you zeroed verses where you are shooting now?

[Bean Counter]

don't give me too much credit. I've never personally reloaded once in my life. I get what powder Federal gives me, and I'm just barely smart enough to buy the same caliber and grain weight consistently 

[300rum]

There can be differences Lot to Lot but I wouldn't expect that much difference.  Something went haywire more then likely your scope/mount. 

[Bean Counter]

I have Leupold high rings. Maybe that's it? But I didn't clang and bang it. I picked the weapon system up by the scope a few times as if it were a handle. Could that have done it?

[2labs]

temperature difference and a really sensitive powder?  Maybe the swing in  chamber pressure is causing the bullet to leave the muzzle at a different point in its vibration or recoil?

Pressure changes with altitude, but temperature and humidity also change it so an increase in altitude of 3000 physical feet might be effectively a lot more if you sight in at sea level on a really cold day with no humidity and then climbed 3000 feet higher and shot on a really hot, humid day.  I can't imagine any change in weather that would cause that much of a shift though.

 

What powder are you using?  If you're not using a temp stable powder you could see that much shift.  What were the environmental conditions when you zeroed verses where you are shooting now?

Not a chance. If this is true,rifles would make better clubs.