400 YARD ZERO.

Question out of my ignorance. If all I have available is a 100 yard range to zero my scope but I want the zero at 400 yards how is this accomplished?
My ballistic data shows that if the rifle is zeroed at 400 yards then the 168 grain BTHP will be + 9.0 inches at 100 yards.Do I hold the crosshairs +9.0 above bullseye @ 100 yards and adjust scope to this position or do I hold the scope crosshairs on the bullseye and and set the bullet point of impact +9.0 inches above the bullseye center @ 100 yards ? Any helpful info or links would be appreciated.

point of impact will be 9" above bullseye at 100

More correctly the point of impact should be 9" above the point of aim at 100yds.

Zero your scope for 100 yards, then adjust up 9 inches. If your scope has 1/4 inch clicks go up 36 clicks, if 1/8 inch go up 72. That should get you close, but I have found that going off of charts I find online I'm never dead on. There are just too many variables involved, however, it will get you in the neighborhood.

If your scope has 1/4 MOA clicks (which is what most scopes are graduated in rather than inches), 9" falls right between 34 and 35 clicks.

You might be better off if you actually place a mark 9 inches higher than your aiming point on your 100 yard target and sight in to hit that mark. Sometimes you have unexpected x-talk between windage and elevation adjustments. Dialing in elevation can sometimes move point of impact to the right or left. A lot of scopes (even expensive ones) don't have consistent or accurate adjustments.

Just out of curiosity, why do you want a 400 yard zero? Most hunters are well served with a zero somewhere between 100 and 200 yards, and will hold over for longer shots if necessary.

Have fun and be safe!

Keith

I want to shoot silhouettes out to 500 yards. This way my only negative number is past 400 yards and with a 400 yard zero my round @ 500 yards will drop approx.-21". This is easy number for me to remember. 3X7=21

my dope says 168 bthp at 2600 fps is only 18.2 low at 500 with a 400 yard zero. remember at 500 yards you multiply your correction x5 examp if i put two minutes up in my scope that is 10 inches at 500 yards

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Originally Posted by rez187

my dope says 168 bthp at 2600 fps is only 18.2 low at 500 with a 400 yard zero. remember at 500 yards you multiply your correction x5 examp if i put two minutes up in my scope that is 10 inches at 500 yards

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My chart states a -20.1" @ 500 yards with a 400 yard zero. -21 is much easier number to remember than -20.1"
These are APPROX NUMBERS ONLY because of too many other VARIABLES. Some time on the bench will tell me exactly where my particular rifle is shooting with a particular load @ 500 yards.

http://www.ultimatesniper.com/Docs/32.PDF

you can also zero the rifle at the first intersection of line of sight and the bullet rise path.

for example, for my 308 and 150gr bullets flying at about 2625, i would zero for 30 yards and be zero'd for about 240 yards which means for hunting i can just put the crosshairs centermass on the shoulder and hit vitals all the way out to about 300yrds.

now i know for target shooting that isnt precise enough but sighting in at 30 yards is a lot easier than sighting in at 100, besides for a 400 yrd zero you would need to zero at like 15 yards or so.

now i have a leupold cds scope so all my range marking are a turn away all the way out to 600 yards.

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Originally Posted by ljv308

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Originally Posted by rez187

my dope says 168 bthp at 2600 fps is only 18.2 low at 500 with a 400 yard zero. remember at 500 yards you multiply your correction x5 examp if i put two minutes up in my scope that is 10 inches at 500 yards

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My chart states a -20.1" @ 500 yards with a 400 yard zero. -21 is much easier number to remember than -20.1"
These are APPROX NUMBERS ONLY because of too many other VARIABLES. Some time on the bench will tell me exactly where my particular rifle is shooting with a particular load @ 500 yards.

http://www.ultimatesniper.com/Docs/32.PDF

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I think you really hit the nail on the head with your comments about sitting at the bench...shooting to 500 yards with your load and rifle. I've used a ballistics program for many years with excellent results. But...I did find in one of my .308's...that when I got past 350-375 yards...my dope was off....I needed a couple of extra clicks in elevation. Guess the data is a very educated place to start.

Good Luck,

Wayne

alot of variables did you input the bullets b.c ,mv, temp, humidty, pressure. i run mine thru a chrono and input all that and more but if you change to a different bullet it will change impact. as getting it close i use to put 2 orange dots 1 center @ 100 then the oher and what ever distance i was going to zero at aim at the 100 center then adjust till bullets hit the 2nd orange dot . still do it when i'm lazy and dont want to move my stuff over to the 300 yrad line and reset up. but nothing can replace actually shooting at the longer range wind at 100 doent move the bullet like wind at 500 yrds.

sendero fan i agree you need to shoot, but math is not a guess enter the right information and you get almost exact results. a few clicks past 300 is allot of error my suggestion would be use a better ballistics program. allot of the programs have a "simple" mode that requires less input but that equals less quality output. Ive found that the program i use after entering everything including the Coriolis effect is so accurate its not even funny. but yes you have to shoot to verify heck that's the fun of it shooting!

What I was suggesting is that computer models are...in the end...a model. There are many variables involved with generating data ( dope )...and a slight variation in any of those data points will throw things off. I still believe it's best to verify by shooting at distance. My Exbal program, I have found, is extremely accurate....bu that one time...the dope was off when I got out past 350 yards. Could be many, many things...scope adjustments were off from the factory....difference in bullet weights, seating depths or charges...don't know...but I did make alteration to my data at that time...wouldn't have known it unless I shot at distance. Computer generated data is great...but...shoot and verify.

Wayne

I use "JBM" and it is fairly accurate but, unless you plug in correct altitude, temperature, humidity and barometric pressure, you will be off to some degree.