Drop change at altitude?

[Fast14riot]

I do most all my shooting under 500'ASL and even at seal level. I will be going to a long range match at 3,800 feet, not having dealt with much altitude change in my shooting, what could I expect? Temp and pressure will be nearly the same, just altitude change. I will run my numbers through a calculator, but just to be sure things line up, I'd like to have an idea of where it should be.

110gr BTHP, .360 BC G1
2700 fps

-Alexander

 

[Sniper338]

Air is thinner the higher up you go. You will see a velocity increase, and less drop due to more velocity.

ie - you can shoot futher more accurately, before hitting the transonic barrier and your bullet going goofy at higher altitudes.

 

[XBBR Shooter]

Air is thinner the higher up you go. You will see a velocity increase, and less drop due to more velocity.

ie - you can shoot futher more accurately, before hitting the transonic barrier and your bullet going goofy at higher altitudes.

I used to shoot very long range matches, and I have never had bullets get "Goofy" - there is no "trans sonic barrier". It is a myth.

If there was such a thing, then how could snipers make the 2,000+ meter shots that they are now making on a fairly regular basis.

 

[chkunz]

There is a transonic region Mach 0.8 to Mach 1.2. Some bullets are effected more than others in this region.

 

[Fast14riot]

I won't be going transonic, don't have that problem on hot days at sea level anyways, but wondering more of how big a difference I might see.

-Alexander

 

[mikecr]

MV won't change.
If conditions other than altitude really do stay the same(temps, MSL adjusted pressures, ~RH) your local BC would go from .360 to .403.
Provided the format gives you sighters, then wind hold-off would be the sole significance to this change.
15" difference per 5mph crosswind at 1kyd.
It's not a LR bullet, that's for sure.

 

[284winner]

Assuming you'll be shooting 1k when you say long range. The difference in your elevation at 1000 yds going 550' to 3800' in elevation will be roughly 5 minutes difference. You'll need 5 minutes less elevation with the 2750' extra terrain elevation. Temperature will also come into play in that formula.

 

[savagedasher]

Air Water grains Just like tunning a car . Larry

 

[Fast14riot]

Not shooting 1k, out to 800 yards. Thanks for the tips, I'll run my numbers through a calculator to get close. We are allowed sighters too, so it will be nice to confirm. But, sighters are only at 2 of the 3 burms

-Alexander

 

[284winner]

Around 30.5 minutes at 500' elevation.
Around 27.5 minutes at 3800' elevation.
Try out the 27.5 at your range. Should be close. They are hardly ever spot on but they get you on the paper at whatever range your punching

 

[Ned Ludd]

Going from San Diego (~500 ft elevation) to Raton (~6600 ft) there is a significant difference in drop. A good ballistic calculator such as JBM will give you a reasonable starting point, enough to get on paper, at least.

 

[CharlieNC]

Why did you say pressure will be the same? You can't go by the weather report, which is altitude compensated. The actual station pressure will be significantly different with that altitude change. Plug the conditions into a ballistic calculator, and select the option for standard temp and pressure for that altitude to see the impact.

 

[swd]

Alexander if your going to Palomino use 4250' and yes there's a big difference in drop going from the valley up to Sparks.

 

[Fast14riot]

Station data today reads 29.79 at the range I normally shoot. The station data for where I will be shooting is 29.87 today. Humidity is usually a bigger delta between locations, but shows less difference in drop. I'm seeing about 1.5 MOA less drop at 500m on the calculators.

-Alexander

 

[swd]

1.5 MOA should be very close. You'll have enough time before the shoot for 10-15 shots to verify and fine tune everything. See you up there!

 

[Fast14riot]

1.5 MOA should be very close. You'll have enough time before the shoot for 10-15 shots to verify and fine tune everything. See you up there!

Yeah. I'm thinking of slinging at least two per burm to check it out. Now just to find time to load ammo this week! I'll be shooting an AR and should be fine with my current dope adjusted.

-Alexander

 

[swd]

There's a guy that occasionally shoots a 6 Fat Rat AR and does very well with it. Have good wind dope. Gusts in the late morning to 30+ aren't uncommon and you don't have time to really wait it out. It's a really fun shoot and good people!

 

[Fast14riot]

I'm shooting 6.8 and have good, verified dope for my local atmospherics, it's put me on the podium at Folsom before. Hope to place top 10%, but I won't hold my breath.

-Alexander

 

[DocUSMCRetired]

I have to completely disagree that the transonic barrier is a myth. Here are a couple shots from Robert McCoy's Modern Exterior Ballistics where you can clearly see that barrier is real.

 

[DocUSMCRetired]

To reply on the OPs post.

1. Use a 100 yard zero, this means the zero won't be effected by changes in environment.
2. Account for Aerodynamic Jump when you zero, this can cause a tenth of a mil shift.
3. Temp would be the factor that most effected your zero. If temp is the same, your MV should be relatively the same, but its still good to know your MV shift per 10 degrees of temp shift (if you are using a very stable powder). Powder Stability can range from .3 to 3 FPS per degree, so knowing this is very important.
4. The change in altitude (going higher) as well as it being summer means thinner air. This means you won't need as much drop to get to range.