Elevation effects on bullet trajectory

[WYODAN]

I have been using a buddies spare BR2 but was looking at SIG because of size. Making me rethink my decision.

 

[oldmossy]

It may be something other than the sig when it comes to my shots hitting where they do. I can only tell you that experimenting with it during different temps, didnt give me much of a variation for adjustment. I was hoping someone would chime in and tell me what my problem was.lol

 

[LRNut]

We live and shoot at 2800 elevation. We hunt at 8000 elevation. I haven't kept a log sheet through the years like Im doing now. But I do know that every trip, my buddies shoot high when we test our rifles before we hunt. I always did too, until I bought the BR2 rangefinder. Whether it does what its suppose to do, and adjusted my hold for higher elevation( I will discuss this more in a second). Or I was lucky could be argued I guess. But while my buddies shot multiple shots adjusting their setups, I fired 2 shots. One at 450ish- direct hit. One at 1300ish- half moa left. Cant remember the exact yardage, shooting at rock faces. And I was shooting my 7mm Allen mag at the time if anyone wondering. So gauging from my experiences, plan on adjusting your scopes once you arrive.

More about rangefinders....

I sold my BR2 and purchased a sig sauer 2400ABS because its more compact. And haven't taken it out west yet. However, shooting and getting my data at home at 60 degrees. Then shooting again at 30 degrees. My sig sauer didn't compensate adequately. I didn't chrono my rifle at 30 degrees, like I did at 60 degrees. But according to my drop data(using very good groups). It appears my gun shot well over 100fps slower. Dropping 1.5 MOA more at 615 yds than when shooting at 60 degrees. My gunsmith, which is a successful competition shooter logs all his shots. He tells me than for every 10 degrees in temperature change, he dials differently for same yardage( about .5 MOA per 10 degrees). It looks to me like my BR2s did that for me. But the Sig sauers aren't. And testing RFs one another day, I ranged 557 yards out my door with Rf temp at 73 degrees. Which was my temperature in my house. Zero angle. Then I hung my RF outside for awhile. Then ranged same target at 38 degrees. and with temps rising that day to almost 50. I ranged again at 40, and again at 50. At 73 degrees it said 8.58 MOA. At 38 degrees it said 8.65 MOA. So .07 change in 35 degree swing. Not even close to what I've experienced while shooting. Or what my gunsmiths data suggests.

Even though I've been shooting long-range for years, It seems like the more I learn the harder it becomes. I'm definetly keeping a log going forward of every shot I fire. Temperature, humidity, what my RF tells me to dial, shot angle, and actual bullet impact. The more I shoot, the harder it seems to be to get a first round 1/2-3/4 MOA direct hit from one day to the next.

Any suggestions on why my sig sauers didn't compensate adequately? Will this RF account for pressure from 2800 feet to 8000 feet like Im assuming the BR2s did?

I'm aware I didn't really answer your question. But figured maybe someone could shed some light on why my RFs aren't adjusting properly. And maybe open the door to you purchasing a RF that elimates the issue you are questioning.

I have the BR2 and the SIG 2400. I live in both Arizona and CO; my Colorado place is 8750; I am there now and shoot at gongs several times daily. The SIG does correct for elevation pretty darn well. At 715 yards my change is about 1 MOA less elevation; I don't know what it is at 905 because I go from 860 to 1200 in Arizona.

As for temperature, I am it total disagreement with the effects of temperature. In the past two months I have shot at temps from -4 to 42 and I don't recall having to move more than one click, if at all. It seems (gut feel here) that shooting in temps over 100 at ranges over 1000 yards you do need to adjust, but certainly not as much as your gunsmith recommends.

I know I haven't bothered to let my SIG sit outside to register the temp; it just doesn't matter, at least out to 905 yards. A bigger affect is aerodynamic jump, which the SIG compensates for but the BR2 does not (nor does it compensate for spin drift, which makes a bigger difference at 900 yards than temperature does IMO). My last shot today was at a 715 yard gong; the wind was blowing about 20 mph but at an angle; my SIG said 2 MOA windage (based on my input) but said come down one click from the day before (wind was from the right). I hit 2" right of center; perfect elevation.

One problem I have with the SIG and BR2 in Phoenix is overheating - if they sit in the sun they will heat up and think it is hotter than it is; why the BR2 is black is beyond me; horrible idea - the old Ranging monocular coincidence rangefinder (I am dating myself) was black too and would heat up and give bad results; painting it white really helped that problem.

 

[oldmossy]

Thats good info to hear. Appreciate the feedback. And idea why my gun wouldve dropped 1.5 moa more than from previous outings?

 

[LRNut]

Thats good info to hear. Appreciate the feedback. And idea why my gun wouldve dropped 1.5 moa more than from previous outings?

I reread your post; you said your MV dropped 150 fps; that is really significant. I once tested spherical powders in hot/cold and got over 100 fps difference, but the temp was pretty drastic. Are you using spherical powders?

The point I was making is that IF you mv doesn't change, it takes a really big change in temp to have any meaningful impact on trajectory.

Maybe you did something dumb like load some rounds with less powder; a few months ago one of my 28 Noslers suddenly went from 3000 to 3250 - and definitely overpressure. I pulled a bullet when I got home and much to my chagrin, I found I charged 87.5 instead of 78.5 gr of RL33. Did the same thing when I sold a car last month: advertised a 2013 Corolla for 4300 - got hammered on CL. Took the first buyer and called him - I told him the price was firm at $3400. When I went to delete my ad, I saw I had it at priced to go for $4300...gulp. He got a hell of a deal.

 

[oldmossy]

I didnt load the shells. My gunsmith did. So anythings possible.

 

[oldmossy]

I havent chronographed yet. Im just assuming its slower based off the bullet drop. Only check I did was my 200yd zero. Which was still on.

 

[oldmossy]

 

[oldmossy]

 

[oldmossy]

Virtually no change in impact dealing with humidity out to 1k yards. Video 29 if someone wants to watch that one

 

[Jim’s Hunt]

We are preparing for a mule deer and antelope hunt. Our home shooting range is approximately 3200 ft elevation, and the hunt area averages 6300 ft. My question is how much will the elevation change affect point of impact. Rifles will be zeroed at 200 yds.

Barometric pressures and humidity plus elevation will be your biggest concern

 

[LRNut]

I watched the first 1/3 of that video; completely misleading. There is no way you are going to be a mil high at 1000 yards based on a 20 deg temp change. I ran his load through JBM; a 20 diff results in .6 MOA less drop at 1000 yards. When I left the video, he was getting ready to explain "internal ballistics" - I assume he is going to blame a 20 deg difference for most of the effects of a high hit (higher MV). He needs to shoot temp insensitive powders if he is getting enough MV diff to cause a hit that high at 1000 yards.

Not sure if he addressed it in his video, but one way to combat the effects of a changing conditions is to shoot a high BC bullet. I just ran the same numbers on a Berger 195 7mm at 3000 fps; a 20 deg temp change results in .2 MOA difference at 1000 yards.

Most shooters think BC is a static number, but it changes as environmental conditions and velocity change. If you plot BC vs drop, you will find bullets with a very high BC don't perform much better than another with a BC .05 higher. But run the same comparison with a low BC bullet, and you will see a marked change. Thus, changes in temperature have a much greater impact on low BC bullets than high BC bullets.

FWIW, I don't find humidity changes to be a big issue; JBM confirms that - the Berger above drops .1 MOA less in 100% humidity than 0% humidity. Elevation changes are by and away the most important.

 

[oldmossy]

I have 3 experiences ive personally seen.
1- yrs ago hunting groundhogs during the summer. I could shoot a pig at 300 yds early in the day. And that afternoon, same hold, same hole, miss high when the temperature was alot hotter.
2- The first time I shot my rifle in question past 200yds. Me and my friend each had our identical custom rifles fresh from gunsmith. After he broke in rifles and developed loads and we got 200yd zeros. I began shooting them at daylight on a cool sept morning. Wanting as cool a temp as possible. Since we shoot specifically for hunting. Shot our first shots. Firing each rifle 2 shots at 767yds. Then going to check target allowing barrels adequate cooling. Wanting a cold bore ritual if u will. Got moa fine tined, Then fog rolled in and I couldnt shoot until much later. Then once fog burned off I continued shooting. Over the course of about 3 hrs between first shots and last shots, the temperature rose alot. Im thinking 30plus degrees. My last 2 shots from my rifle was less than 3 inches at 767yds with my rifle. And amazingly for my ability, 1.5 inches shooting his gun. Still, only two shot groups per rifle. But rather good in my book. However, those last shots were almost 1 moa higher than when we started. As the temp increased throughout the day we had to keep dialing less.
3- the day in qusetion. 30dergree dropin temp..1.5 moa drop in impact.
Im not disagreeing with your real world data. Im simply trying to figure out what could be causing me to see such a swing in impacts. I shoot off a backpack to simulate real hunting. And I shoot as much free recoil as possible to try and limit my influence on the rifle. Im just a hunter. No training or guidance other than reading on this forum and watching youtube. Still learning. And also learning that sometimes things dont work like Ive already proved to myself they do.lol

 

[LRNut]

Well, there is one other scenario: mirage actually displaces the target slightly. When it boils up, you can hit a bit high due to that, but I wouldn't call it a temperature impact per se. IME, the effect is more pronounced in high humidity areas than low (like in the West).