Help Reverse Engineering DOPE

[Doc Holliday]

I have a bit of a conundrum. I have shot out to 100, 200, and 300 yards using my x-mas tree style reticle for holdover. The way the range I go to is set up, it skips from 300 yards to 600 yards, and nothing between. So Im now trying to figure out my holdovers for 400 and 500, but am thinking maybe I need to take a different approach.

My reticle subtensions are in cm at 100 meters, and my elevation and windage move in .1 Mil increments or .36" @ 100 yards.

DOPE:

• My 100 yard POI is the center crosshairs
• My 200 yard POI is at the hash mark that represents 10 cm drop at 100 meters
• My 300 yard POI is at the hash mark that represents 17 cm drop at 100 meters

I plan to shoot at 600 yards next weekend, but not sure what accomplishes if I don't know where 400 and 500 are.

I do not have a chronometer

Any ideas? I've got less than 2 weeks to try and get this figured out

 

[Formidilosus]

I have a bit of a conundrum. I have shot out to 100, 200, and 300 yards using my x-mas tree style reticle for holdover. The way the range I go to is set up, it skips from 300 yards to 600 yards, and nothing between. So Im now trying to figure out my holdovers for 400 and 500, but am thinking maybe I need to take a different approach.

My reticle subtensions are in cm at 100 meters, and my elevation and windage move in .1 Mil increments or .36" @ 100 yards.

DOPE:

• My 100 yard POI is the center crosshairs
• My 200 yard POI is at the hash mark that represents 10 cm drop at 100 meters

What cartridge/bullet are you shokting that had a 1 mil drop at 200 yards?

• My 300 yard POI is at the hash mark that represents 17 cm drop at 100 meters

You have something wrong. You aren’t dropping 1 mil from 100 to 200, and then only .7 mils from 200 to 300y.


Mehta is the scope and reticle?

 

[Doc Holliday]

What cartridge/bullet are you shokting that had a 1 mil drop at 200 yards?





You have something wrong. You aren’t dropping 1 mil from 100 to 200, and then only .7 mils from 200 to 300y.


Mehta is the scope and reticle?

Its a .270 Win handloaded 140 gr Ballistic Tip with 51 gr of Reloder 19. Nosler manual gives a 2779 velocity out of a 24" barrel, but Im shooting a late 90s Browning A-Bolt with Boss, so there's only about 18 inches of rifling.

 

[Formidilosus]

That load should put you very close to an average gun.

100- 0
200- .5 mil
300- 1.0mil
400- 2.0mil
500- 3.0 mil
600- 4.0mil

 

[SomeJackassOnAForum]

Are you trying to say that your drop from 200 to 300 is 17 cm @ 100 m beyond the 10 cm to get from 100-200?

If that's the case, your gun is needing drop like my 7.5" barreled 7.62x39 AR.

If you're saying you need 1 mil at 200 and 1.7 mils at 300 it's shooting like my 11.5" 5.56 AR.



If you want to work this backwords, we'll need:

-Sight height above bore
-G1 BC of your bullet
-Confirm the drop you need in that reticle and that you're dead on at 100 yds.

 

[Doc Holliday]

Are you trying to say that your drop from 200 to 300 is 17 cm @ 100 m beyond the 10 cm to get from 100-200?

If that's the case, your gun is needing drop like my 7.5" barreled 7.62x39 AR.

If you're saying you need 1 mil at 200 and 1.7 mils at 300 it's shooting like my 11.5" 5.56 AR.



If you want to work this backwords, we'll need:

-Sight height above bore
-G1 BC of your bullet
-Confirm the drop you need in that reticle and that you're dead on at 100 yds.

Saying I need 1.7 mils at 300, and 1 mil at 200

Sight height above bore: 2.25 inches
G1 BC: .456
Yes, dead on at 100 yards...possibly .1 Mil high

 

[SomeJackassOnAForum]

So your 200 yd hold is the blue line, and your 300 yd hold is the yellow line or the green line?

 

[Doc Holliday]

So your 200 yd hold is the blue line, and your 300 yd hold is the yellow line or the green line?

View attachment 576678

Yellow is 300 yards point of impact

 

[SomeJackassOnAForum]

Yellow is 300 yards point of impact

Can't even get close to that ballistically.

To have 1.7 mils of drop @ 300 with your values, you get 0.7 mils of drop at 200. (2350 FPS)
To have 1 mil of drop @ 200 with your values, you get 2.3 mils of drop at 300. (2100 FPS)

My recommendation would be to get a ~36" tall piece of paper. Shoot a 5-shot group at 100 near the top to confirm zero, then shoot that same point of aim (no correction, no holdover) at 200 yds, and then repeat this at 300 yds. Measure in inches and take pictures of the groups with a tape measure next to them from the aiming point.

Alternatively, I'd get on amazon and order a chronograph.

 

[TxLite]

Is the optic SFP and are you changing zoom between yardages?

 

[EdP]

The chronograph data and any of the ballistic calculators available on-line should give you what you need to solve most of your issue. It will be best in my opinion if you bought a chronograph that does not attach to the rifle barrel. Otherwise you will have to shoot for ballistic data and for groups/POI separately. Still entirely doable though. Other than that, I would suggest you zero at 200 yds. A 200 yd zero will come very close to maximizing your point blank range. Be sure to let your barrel cool between shots. As Form said, there is something wrong if your drop between 200 and 300 is less than your drop from 100 to 200. Bullets don't gain speed with distance from the muzzle.

 

[Rock-o]

Internet search for "weaponized math". You'll find a table with data to get you off and running.