Range Report JBM question

[45-70-500]

Another newbie question.In the JBM calculator do I enter the 20 MOA difference in my scope base under Elevation or does it not matter. I've tried entering it but the end result between this and entering 0 is the same. Was out for the first time last night on the DND range shooting 600 metres with a rifle sighted in for 200m. Using 44Gn of Varget behind a AMAX 168, 308, in my Remington SPS and all I needed was 31 clicks or 7.75 MOA to get on target. Can't match this up on the JBM. What am I doing wrong.

 

[bohem]

Re: JBM question

How much is it not matching by?

The only time I ran a tapered base I just told JBM it was going to get a flat base (0 MOA) and subtracted 20 MOA from what JBM told me to use.

For a 100y zero, getting to 600y should take you about 15 MOA with that load (approximately), if you're dialing back 7.75 minutes from a 20 minute base, it's taking you 12.25 MOA to get there from your 200y zero.

As I understand it, that's what you're doing. You need to subtract that 7.75 from 20.

Maybe I'm not getting what you mean though.

 

[Boomholzer]

Re: JBM question

As long as your zero is true and your optic axis to bore height accurate; you should be OK.

Make sure you check "elevation correction for zero range" box at the bottom.

Are you using the same zero range in calculation vs at the shooting range?

 

[45-70-500]

Re: JBM question

Bohem, i like your thinking but when I do the math there seems to be 10 MOA missing some where.Until I shoot all the other distances I can always subtract the difference in the 600 setting from the other drop calculations just to get on paper quicker.

Boom ,that box was checked and I had the rifle zero'd at 200 and just adjusted the scope to hit 600.

 

[Rob01]

Re: JBM question

There are lines between the sections on JBM trajectories http://www.eskimo.com/~jbm/cgi-bin/jbmtraj-5.0.cgi so i will tell you what to fill out in each section.

First section- either bullet from library or the info if it's not there

Second section- velocity from your chrono and distance

Third section- Just sight height. Nothing else.

Fourth section- wind speed and leave direction at 90 as that is full value. I like to use 10mph as I can adjust off of that.

Fifth section- Target speed if you need that. I use 2 mph which is basicly walking speed and what most movers I have shot are set at.

Sixth section- The ranges you want with 200 being the zero range

Seventh section- Your info for temp, elevation, pressure if you know it and if not leave what is there and I use 60 for humidity as it's average and that number doesn't make much difference anyways.

Eighth section- Your drop units. You have an MOA scope from your first post so make the first one MOA. Not clicks but full MOA as you use the big numbers on the dial to dial on the elevation and don't count clicks. The second one can be what your reticle is in. If it is mil based make that mil. I don't use vitals or energy but feel free if you need them.

Ninth section- Leave what is checked like it is and then check ranges in meters because that is what you use obviously.

Now click calculate and you are done. I have been using JBM for years and that is how I do it and get the proper info all the time. Make sure to put the right info in or you won't get the right info out. Don't worry about a 20 MOA base. It doesn't need to be put in anywhere.

 

[BobinNC]

Re: JBM question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hksl8</div><div class="ubbcode-body">Another newbie question.In the JBM calculator do I enter the 20 MOA difference in my scope base under Elevation or does it not matter. I've tried entering it but the end result between this and entering 0 is the same. Was out for the first time last night on the DND range shooting 600 metres with a rifle sighted in for 200m. Using 44Gn of Varget behind a AMAX 168, 308, in my Remington SPS and all I needed was 31 clicks or 7.75 MOA to get on target. Can't match this up on the JBM. What am I doing wrong. </div></div>

hks18,

You really don't provide much information like: What velocity you are using, and what scope, what altitude, et al....

As Rob said, what MOA your base is not relevant...So....

But after much calculating I came up with this:

Velocity 2700 FPS
Zero @ 200 Meters
Comeups for 600 Meters = 32 Clicks

The click value I used was 1/2" clicks or 15.5 MOA. Are you sure your scope has 1/4" clicks? Inquiring minds want to know?????


Bob

 

[45-70-500]

Re: JBM question

Bob judjing buy the numbers you got I will have to double check as you are bang on. Its a Falcon Menace and I confirmed on the website 1/4" clicks. I have the velocity at 2650, best guess using the Hodgon site. We are about 850' above sea level.

 

[BobinNC]

Re: JBM question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hksl8</div><div class="ubbcode-body">Bob judging buy the numbers you got I will have to double check as you are bang on. Its a Falcon Menace and I confirmed on the website 1/4" clicks. I have the velocity at 2650, best guess using the Hodgon site. We are about 850' above sea level. </div></div>

Which Falcon Menace? The Falcon does come in two flavors that I know of, 1/4" Clicks, 15 MOA per revolution, and Metric 1cm/0.1 Mil or 60cm/6 Mils per revolution.

Oddly enough, from a 200 Meter zero, to hit 500 meters (not 600m, which would require 44 0.1 mil clicks), with a Falcon mil/mil scope is also 31 clicks (0.1 mil clicks)...Hmmmm


You might need to do a box test on that scope, to find out what you really have. 1/2" clicks (that would be weird, and different, but it is the only value that works at 600 meters), 1/4" clicks (doubtful given the ranges) or 0.1 mil clicks (possible if you were at 500 meters instead of 600 meters).

Let us know the verdict,

Bob

 

[BobinNC]

Re: JBM question

hks,

The more I think about it, the more I think you may have a Falcon mil/mil scope with 1/4" dials. With a 1/4" Falcon 31 clicks is a little more than half way around the dial, or 7.5 MOA. 31 clicks on a 0.1 mil Falcon is 3 mils, also a little more than half way around the dial. But 3 mils is 11 MOA @ 500 meters.

If your scope is really a mil/mil Falcon with 0.1 mil adjustments, and your range is 500 not 600 meters, than 31 clicks would bring you right on target.

You got some things to check out,

Bob

 

[wadebrown]

Re: JBM question

Do a box test I have a Falcon with 1/2" clicks at 100 yards when it is supposed to be 1/4". As soon as my NF gets here I will send the Falcon back for repair.

 

[45-70-500]

Re: JBM question

Sorry guys for wasting your time.Haven't needed to pay attention to the adjustments sinch it was sited in. Now my first night shooting what I think is a long distance and we were all talking MOA but just noticed the scope adjusts 1cm-100m per click. Makes alot of sense now. The scope was such a deal at the time I guess the setting weren't a concern.

 

[shooter308]

Re: JBM question

this is cool

 

[sobrbiker883]

Re: JBM question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Shooter308</div><div class="ubbcode-body">this is cool </div></div>

Ona side note-Really, why do you post all these useless one-liners (that rarely make sense)?!?!?




hksl8-now there's a find! at least you know what's up now. Your scope has .1 mil adjustments. Now you just have to get MOA out of your head and carry on!

 

[45-70-500]

Re: JBM question

Well that wasn't the problem. Still have to get to my regular range so I can do a box test but shooting the long ranges has me following the 1/2" JBM table to the letter. Will get back to you after a box test hopefully next week.

 

[Apache]

Re: JBM question

sorry to deviate from the initial question, but I have a JBM related question, under the "sight height" category, where do you measure from and to? Such as: bore to middle of objective lense? or to where the it first touches the scope?

 

[Rob01]

Re: JBM question

Measure as below with either a ruler or caliper and it will get you close enough. It's how I have been doing it for years with JBM and it works very well.

 

[Lindy]

Re: JBM question

Sight height is not a critical measurement. To test that, just vary it by a quarter of an inch in the software, and observe how little difference it makes.

 

[Apache]

Re: JBM question

Thanks for that, very helpful. I guess I never really noticed how it was not that critical, just assumed it was.

 

[sobrbiker883]

Re: JBM question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hksl8</div><div class="ubbcode-body">Well that wasn't the problem. Still have to get to my regular range so I can do a box test but shooting the long ranges has me following the 1/2" JBM table to the letter. Will get back to you after a box test hopefully next week. </div></div>

You mean 1/2" clicks?? If so, realize any ballistics program will only get you close, not right on, actual field data. .1mil adjustment=.36" at 100 yds. so its an adjustment that is only 1/8 moa away from either 1/4 or 1/2 minute.

If you can get to long ranges, the data you write down each time you shoot at distance will be far better than anything the best ballistics program can tell you.

If you want to check your scope, I recommend the FAQ's in the Optics forum, there's a great writeup on how to do that already.

 

[Lindy]

Re: JBM question

Optically Checking Rifle Scopes

 

[45-70-500]

Re: JBM question

Thanks Lindy and Sobr, will check it out.