Well yesterday I spent a little time at the range with my 7 RM and some 175g uld rbbt loaded with 66.2g H1000 which is good for .5" at 100 yards and right at 2900fps. I wanted to get an idea of the BC so I plugged in .650. Now according to my program with a 100 yd zero, 175g at 2900fps, .650 BC, I needed to have 72 clicks to be dead on at 800 yards. Well after zeroing at 100 yards and double checking the velocity (2900) we went back to the 800 yard line firing on the 15" gong. My first shot impacted about 2ft low according to my friend the spotter. I thought maybe I pulled so I did not touch the clicks and let the 2nd shot go. It impacted in the same spot, about 2ft low. Well now I was pretty discouraged and knew the BC for my drops wasn't .650. I ended up needing 10-12 more clicks to be dead on. So instead of needing 72 clicks, I was at 82-84 clicks. After I got home, I plugged in .6, then .550, .500 and what I found out in terms of drop was that my BC is in the general neighborhood of .500. This seems awfully low to me, but matched up to my trajectory at 800 yards. I feel 800 yards is a fair distance to compute a field drop generated BC. I did not shoot any groups, but I had no problems hitting the 15" gong off the bench once my zero was confirmed. There was little to no wind. Just thought Id keep ya'll informed.
Just a thougt on your B.C. On the program did you happen to put in the temp and altitude. It will also effect the trig. of the bullet. I might be going on a limb but I remember some one talking about the twist of the barrel, and how it also can influece the B.C. of the bullet which might be why you were seeing the difference. I can't remember exactly where.
Yes, I did take the temp. and altitude into consideration. The only thing I dont take into consideration is pressure and humidity and only because I have no ways of measureing it. I am pretty dissappointed in my findings. I would have thought the BC to be a lot higher then what it come out to, under my conditions anyways. I think I might just stick with the 162g amax since its got a relatively high .625 BC and they are the cheapest/highest BC target/hunting bullet I can think of right now. I also want to try the 180g VLD. Its suppose to havea BC around .685. I have found Bergers to be pretty spot on as far as BC goes. I;ve shot the 168g vld out to 800 yards and the projected BC of .643 matched up perfectly for me out to 800 yards.
With pressures in the 30s you are pretty low in altitude and may well be experiencing the same phenomena as Mike & Tim in TX. Their BCs for the same bullet are running as much as ~0.2 below mine for the same bullet and velocity and pretty much identical rifles. They are at something like 195' MSL and I'm @ 4450' MSL. Bullets are 169 WCs and 150 NABs and BTs. Go up into the Blues and you'll see a bit of a difference, though that is still a pretty low elevation.
Here's a link to more than you need to know about the weather in Hermiston. Book mark this the write in your log book when you head out.
As Roy mentioned the pressure and humidity, will definately alter your BC. Down here in the balmy south, trying to shoot in like conditions is a hit or miss propisition.
For the most part, our BC for the Wildcats are running from .6xx to .7xx depending on the conditions at the time. The hard part about it is that it can go from 40-60% humidity which is relativly mild to 80% or more in just a few hours with a change in wind direction. THe pressure is more of a constant, but still averages around 30 for the most part. All this does is compress all the air and when we get those high pressure systems you can literally feel it being squeezed around you.
WE get the same thing in our distance casting. We have folks come in from up on the East coast and from over in England, who hit out past 800ft on a regular basis at home. They literally struggle to hit mid to high 700' cast down here. Same principles apply.
Save up a little and pick you up one of the Kestral wind meters which will give you current on-site conditions. Tim got one and it has helped us to adjust for the quick changes around here.
i'm not a big fan of using clicks to determine the drop of the bullet.a better test would be to zero at whatever range and then put a tall enough target at 800 and shoot again not changing the scope. now measure the amount of actual drop and figure the BC based on this number. more accurate in my opinion.
as a side note i once looked at the difference in drop based on altitude alone.from 1500 to 9500 the difference at 2200 yards is around 50 ft. yes i said feet!
Mike, yall aint got me into no crazy math stuff did you? Does a nightforce come with a cal-cu-later? And what recticle you and Tim using? We gonns have to get together for class....you know Southerners need all the help we can get!