Making accurate drop chart - who to trust?

[dRb]

Ok, so true to my promise after shooting Tiff's do, I've moved all of my useful bits (scope, bipod, cheek raiser) over onto my .22lr, and I've been out practicing.

 

Only issue I'm having is getting reliable drop data to work from...

 

Shooting at a little steel target I've made myself that is a 140mm disc. Using my mil ret on my fixed power scope, I'm practicing ranging the target manually - nothing ground breaking, just 140 divided by the number of mils = range in metres.

 

I'm using Eley Subsonic Hollow Point (40 grain, BC0.14 G1), and I have chrono'd them to 1056fps.

 

All good so far?

 

First up I tried Chairgun on my iPhone...missed high on all solutions before running out of light.

 

Went to JBM's online calculator today and put in all the accurate detail I could, and printed off the chart to go shooting.

 

Missed high.

 

So, for this example my 140mm disc was exactly 1 mil, so 140m range. JBM and Chairgun both suggested 16.2moa up, I got on target with 10.5moa up. First though was that I'd turned one more 6 moa rotation than I thought on the turret, but winding it down 10.5 put me back on zero.

 

Any thoughts?

 

Interestingly g7.com gives something closer to what I used - 12.9moa vs the 16.2moa JBM and Chairgun are giving.

 

[oaken]

No substitute for measuring your actual drops in the field.

The sightron turret wraps that I do almost always have to be redone when made up from computer generated data.

Have you checked the accuracy of your reticle and click values? Is your chrono accurate? Same for your rangefinder. I imagine the ballistic coefficients for rimfire ammo could be wildly inaccurate too.

Put all that together and your predicted drop could be (is!!!) out by a country mile.

Test your drops the fun way- in the field, it's the only way to be sure.

Rup

[tackb]

I use the same ammo and ballistic for I phone is extremely accurate in my experience but as usual sh1t in sh1t out

[Bangbangman]

What Rup said.

 

I shot from 15 to 100yds the other day: Eley subs (a new and an old batch) out of my Sako Quad, standard barrel length. Out of this rifle the chrono (at 10ft) said av 961fps. Rangefinder for distances.

 

My drop at 100yds is 10" when zero'd at 50yds (also zero at 15yds with this sight height.)

 

This is 2" more drop than a published chart (Internet) for the "same" ammo with 50yd zero.

 

Your own field data from your own rifle is confidence-inspiring and will improve your success rate. Just make sure you aren't shooting with a raging head- or tailwind (or gradient), of course.

[dRb]

Is there any software that allows you to enter info including field test results to fine tune the calculated output?

 

Scope values are defo an option for errors - I was hoping that the fixed power would mean that the ret was mil accurate, but I need to get it on a fixed confirmed range and test it I suppose.

[dannywayoflife]

I "think" can input actual target data into ballistic fte to fine tune it. Them my problem with this app is the lack of any instructions

[dRb]

Ok, so based on my understanding of how ballistic calculators work...

 

I buy a reel tape measure, and shoot some fixed distances, measuring drop.

 

At the same time I measure MV for each shot.

 

I then get a good average MV (half a box of ammo meaned), and then put ammo from the same box over the chrony at another fixed range.

 

I should now be able to tweak the BC on JBM to make the trajectory fit correctly for my known distance and MV shots, plus be able to confirm the velocity drop over x metres.

 

Is there any means of confirming the scope/barrel centre spacing? Currently measuring with calipers visually.

[dRb]

Also; whilst shooting at said measured distances, I can test the tracking of my elevation and windage clicks, and test the milness of my mils on the ret.

[Missed]

No matter what scope, I always box test them when they go onto a rifle. By doing the box test you know the actual travel per click of your adjustment at a fixed range, this will save ammo at a later stage when you try and work out why your predicted trajectory fails to marry up with the actual adjustment.

[dRb]

No matter what scope, I always box test them when they go onto a rifle. By doing the box test you know the actual travel per click of your adjustment at a fixed range, this will save ammo at a later stage when you try and work out why your predicted trajectory fails to marry up with the actual adjustment.

Guessing the 'box' is shoot, x clicks right and shoot, same down and shoot, same left and shoot, then the same up to hopefully put another round through the first hole?

[dannywayoflife]

Yep that's it. It also ensures that the scope is set level

[Missed]

That is correct dRb. Be quite bold in you adjustments, say twenty clicks up, right, down and left. Measure the MPI of each group and compare that with the actual adjustments made. Also, as danny has mentioned, it will give you an indication of how level your scope is. Be acutely aware of not canting the rifle also.

[oaken]

For your rimfire, first establish your zero.

I would use 65yds. Also put out targets at 100 and 150. Use level ground.

Set scope to zero at 65yds. Shoot a group at 100, make a note of how many clicks

Do same at 150.

You now have accurate drop data for your setup regardless of any variables.

If your bullet is listed by the program that you are using, adjust the velocity to make it fit. If it won't, then fiddle with the BC.

To check your reticle. On your 100yd target, mark the edge with 3 aimpoints ( more is more accurate) that are 3.6" apart. At 100yds a mildot measures 3.6".

To test your elevation clicks. Shoot a group at the bottom of your target then wind on 40 clicks (1/4min) and shoot another group. It should measure 10.47 inches.

If either of these is out, double check your distance measurement. Though unless you actually want to "range" with your reticle you have drop data from the first excercise that you know is specific to your setup.

Scale up distances for larger calibres.

Getting a mil/mil or moa/moa scope makes life much easier :-)

Rup

[dRb]

For your rimfire, first establish your zero.

I would use 65yds. Also put out targets at 100 and 150. Use level ground.

Set scope to zero at 65yds. Shoot a group at 100, make a note of how many clicks

Do same at 150.

You now have accurate drop data for your setup regardless of any variables.

If your bullet is listed by the program that you are using, adjust the velocity to make it fit. If it won't, then fiddle with the BC.

To check your reticle. On your 100yd target, mark the edge with 3 aimpoints ( more is more accurate) that are 3.6" apart. At 100yds a mildot measures 3.6".

To test your elevation clicks. Shoot a group at the bottom of your target then wind on 40 clicks (1/4min) and shoot another group. It should measure 10.47 inches.

If either of these is out, double check your distance measurement. Though unless you actually want to "range" with your reticle you have drop data from the first excercise that you know is specific to your setup.

Scale up distances for larger calibres.

Getting a mil/mil or moa/moa scope makes life much easier :-)

Rup

Getting new glass is on the list as you know, but for now, I have what I have.

 

I'm off to buy a few hundred rounds today to play with and I will see where I get to.

[dRb]

Part 1:

 

Apparent scope above bore = 1.5"/3.81cm

 

Average MV reading 1015fps from 20rds measured.

 

10m -1.0 cm

15m 0 cm

20m +1.0 cm

30m +1.6 cm

40m +1.8 cm

 

Just need to find some more flat space now to do 50 upwards...

[dRb]

Chairgun results:

 

40grn

0.14 G1 BC

 

10m -1.0 cm

15m 0 cm

20m 0.74 cm

30m 1.39 cm

40m 0.91 cm

 

So I'm fine to start with, but then keep going up!

[dRb]

Looking at the scope height first, the corrected heights vary from point to point, but average at 4.15.

 

Putting this back in...

 

10m -1.1 cm

15m 0 cm

20m 0.9cm

30m 1.7 cm

40m 1.48 cm

 

So although this gets me closer, I'm still going up when I should be coming down.

 

This suggests the projectile is going faster than thought.

[dRb]

Time to re-shoot 30 and 40.

[oaken]

You ARE coming down..... towards your second zero.

First intersection with your sight line, your bullet will be going up at 15yds. Your second will be coming back down at around 65yds.

[dRb]

I know it will be coming back down into the far zero, I meant that the results from the ballistic table were that I should be lower at 40 than 30, rather than still climbing - I'm actually wondering whether I mixed up the 30m and 40m targets :s

 

Got loads more data to look through now, so hopefully I'll have something useful results wise

[terryh]

dRb

 

Do you 'have' to use subs??

 

Even at 100 yards a more 'target' type of bullet is better. We shoot a club comp at 105 yards for score and the one thing that has come out of this is ammo choice for your rifle. Do not think anyone uses or chooses subs that consistently does well?

 

I shoot my 22RF at 200 and occasionally 300. lowest grade ammo would be SK plus. If it's a noise thing target rounds normally run 1050 so 'sub' in effect.

 

Just saying

 

T

[dRb]

dRb

 

Do you 'have' to use subs??

 

Even at 100 yards a more 'target' type of bullet is better. We shoot a club comp at 105 yards for score and the one thing that has come out of this is ammo choice for your rifle. Do not think anyone uses or chooses subs that consistently does well?

 

I shoot my 22RF at 200 and occasionally 300. lowest grade ammo would be SK plus. If it's a noise thing target rounds normally run 1050 so 'sub' in effect.

 

Just saying

 

T

The idea is to get out on steels to 200-300m, so my idea was that subs would not have to worry re transonic etc.

 

Issue is that I wanted some charts to start from, but I can't for the life of me make the real world and the theoretical world match up!

 

I've used drop charts/programs to good effect with my .308, but I'll be buggered if I can get any sense out of any of them relating to what I'm seeing in the field.

 

Bangbangman's nice chart is a thing to be envious of - mine drops in places then recovers!

[dRb]

Attached is a chart showing the first 80m of flight (slowing down and falling) as measured today - the Series 1 line is my results, the Series 2 line is the absolute best fit I could get by basically messing with the MV, scope height, and fractional changes in the POI at the zero range (15m).

 

As you can see it fits 5/8 points on the curve, but my result clearly fall short in the 40m, 50m, 60m areas before 'catching up' on 70m and 80m.

 

My worry here is that the continuation of these lines will show that the line I've forced to fit from the calculator will drop away.

 

I've had to take my measured MV of 1016fps (Chrony F3, new battery, 20 shot string) down to 965fps on the JBM settings!

[dRb]

Plan for tomorrow is to use the chart that makes the Series 2 line from JBM, and try to hit some metal

[dRb]

dRb

 

Do you 'have' to use subs??

 

Even at 100 yards a more 'target' type of bullet is better. We shoot a club comp at 105 yards for score and the one thing that has come out of this is ammo choice for your rifle. Do not think anyone uses or chooses subs that consistently does well?

 

I shoot my 22RF at 200 and occasionally 300. lowest grade ammo would be SK plus. If it's a noise thing target rounds normally run 1050 so 'sub' in effect.

 

Just saying

 

T

Just re-read - if you're suggedting to use target ammo (as in Eley Match/Tenex/etc) rather than practical target (CCI Mini Mag etc), and using 'subs' to refere to hunting rounds, then yes I do plan to move over to match rounds

 

I actually started a thread last night in Varminting asking for peoples experiences.