75yds not 100yds?

[boomer92266]

I set my Ruger American today in my back yard, I have always stepped it off and thought it was close to 100 but it isn't that close. It's 75yds and my shot was 1.75 inches high at 75yds, how will that be at 100, 200 yds? It's a 243 Winchester using Winchester 100 grain Power point ammo. I have looked online but can't find anything, thanks for any help.

 

[Pál_K]

I went to this site:

https://www.federalpremium.com/Ballistics-Calculator
and got the results below, estimating things about your bullet and velocity. Try it out and fill in the info as best as you can to generate the chart. There are many other such sites - just search for "ballistic calculator" and fill in the values.

 

[Pál_K]

This one is closer to your results:

 

[Mobuck]

Not much difference between 75 and 100 BUT any slight variation in zero will be amplified (and more easily noticed) by checking zero at longer distance.

 

[Jeepnik]

I always love those sorts of charts. Mostly they are wrong.

 

[gunzo]

Pal K's second chart is mostly dead on according to JBM ballistic calculations., that I trust & use frequently. I gave it 3000 fps, the Win bullet, 80 deg & 850 feet of elevation which is about average for my county.

 

[Pál_K]

I always love those sorts of charts. Mostly they are wrong.

They're fun to look at and do give an approximation to what the trajectory is.

There are lots of factors which produced that chart which likely aren't duplicated by what someone is shooting.

Ballistic coefficient? If you're reloading, then likely you do know this from the reloading manual and the bullets you've chosen. If using a factory load, it's likely you don't know the BC.

Velocity? That's the hard one. With a Garmin doppler radar chronograph, that's now a lot easier - if you have one. If using factory loads, the velocity given is what they get out of their tests, not out of your barrel.

Temperature, humidity, air density: other factors that create discrepancies.

 

[krw]

I have used JBM literally 1000’s of time. Always be sure to put your actual measurement of CL of bore to CL of scope. That helps your ballistic chart greatly

 

[GunnyGene]

This:

http://www.kevinsworkbench.com/scopecalculator/index.html
Or one of the other ballistic calcs listed on the page.

Or the JBM calc, which is what I use. All of these require that you know the actual MV of your gun (per a chrono), or you can input the factory advertised MV (which is likely off what your gun does).

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

 

[krw]

Bit, you can zero your rifle at 100yds then back off to 5-600 yds and aim dead on and let the bullet drop. Now keep changing you velocity number until it match’s the drop at prescribed distance. Now you know the real velocity on that day under thise conditions

Now go buy a Kestrel weather unit. Learn how to figure density altitude. That is a real world variable on bullet trajectory. Thats why the boys out West can play so much further out than us boys in S Arkansas. We shoot through some humid soup on the summertime. That works on long ranger trajectories!!

 

[gunzo]

I was shooting steel @500 a couple weeks ago & mentioned I had to use my 525 yard JBM produced data to get good center hits.
The host then said that the steel was actually about 525, they just called it 500. My rifle was telling me that & I wasn't listening.
2 lessons learned; do my own ranging from then on & trust my charts, as I give them correct info & & they give me their info back that way.

 

[boomer92266]

Well I got out this morning and asked my neighbor if I could ease over on him to set up and that way I could be 100yds away. I fired a 3 shot group and decided to bring it down as most my shots will be in the woods. Here is my target with 2-3 shot groups, Thanks for everyones help.

 

[peachhead]

Why not just zero it with what you got?
I zero at 25 yds. Never causes an issue.

 

[thinckley]

All of my rifles are zeroed for MPBR (using the same site @maddmatter1970 posted). Doesn't matter if my shots are going to be inside 200 or past 400. Some are set up for Elk with a 9" kill zone, some for deer/antelope with a 6" kill zone, and my RAR in .17hmr is varmints with a 4" kill zone.

https://shooterscalculator.com/

Ballistic coefficient? If you're reloading, then likely you do know this from the reloading manual and the bullets you've chosen. If using a factory load, it's likely you don't know the BC.

I've found that most of the factory ammo I use lists the BC either on the box or on their website.

 

[s4s4u]

Why not just zero it with what you got?
I zero at 25 yds. Never causes an issue.

That really depends on sight height. If you zero an AR in 5.56 with a 2.6"+ sight height you would be all of 10 inches high @ 200 with a 25 yard zero

 

[steveodtw]

Well I got out this morning and asked my neighbor if I could ease over on him to set up and that way I could be 100yds away. I fired a 3 shot group and decided to bring it down as most my shots will be in the woods. Here is my target with 2-3 shot groups, Thanks for everyones help.

You're done! Nice.

 

[Rumrunner]

I use the various charts for a rough reference. Even knowing my velocity by using my chronograph, they still aren't dead on. I'm a firm believer if shooting various distances and making my own charts. Our range only goes out to 200 meters. I can go to my timber and set up for longer ranges, but never have had the need to. Maybe if I'm heading out west...

 

[Shamus2022]

Heck.... I only clicked on this thread because I thought we were talking handguns. I always zero my ACPs and assorted .44s for 75 yds... that way they are 4 up and 4 down (4" high at 50 yds , 4" low at 100 yds)