22LR / DNT Zulus - Interesting results / Calculation Quandry

[12gsnapcaps]

I have a cz 457 in 22LR running SK Standard Plus at 1070fps.

The DNT Zulus v2 in 3-12 is spot on, I have this one and a v1 and love them.

I'm printing thumb nail sized groups at 100 yards so accuracy is not an issue.

However, I've noticed the ballistic calculator makes my shots about 3-4 inches high at 100 yards.

This is with inputting the correct information, which I've triple checked. Speed of 1070, G1 BC of 0.14, Scope height (centre to centre) of 6.1cm etc. Speed has been triple checked with a chrono, HOB checked with calipers. All other info like bullet length and altitude etc, although mostly irrelevant, are all inputted correctly.

Only way I can get the projected aimpoint to match with actual POI is to change the velocity in the optic BC to an incorrect value of 1130 fps. - This gets everything to match up to 114 yards, however I'm not able to test further than this distance. Changing the BC value in the optic BC had no effect, even pushing the BC up to G1 0.20 - Only the faux velocity increase had an impact.

Not had this with any other calibre, only with .22LR - very strange

Anyone else encountered this? Which this scope or any other digital optic?

 

[Cottis]

I have had to correct parameters that I know are correct to ensure Strelock etc spits out correct drops etc with some other rifles/chamberings whilst others are bang on. Not .22LR or the DNT scope you use for me personally but you often have to change some stuff (mostly speed either up or down) to correct POA/POI further out.

I have a DNT4k but have only shot 6mm CF with that and it is perfect with the actual measured data.

So long as your altered input results in it putting the bullet where you need to, I would say crack on. I am sure others will have had to sometimes correct known actual data to ensure firing solutions are given correctly with a myriad of ballistic calculators. I guess in the end, if it works, it aint stupid although I agree it would be nice if inputting your actual known data resulted in the correct outcomes.

 

[12gsnapcaps]

I would imagine with .22LR subsonic, that due to the low BC, low velocity, and extreme accuracy it's users are looking for (thumbhole groups instead of 1-2MOA) any small errors in the calculations, data, are magnified exponentially.

Due to the high BC, high velocity, and more forgiving accuracy requirements (Heart/Lungs of deer rather than rabbits head at 100y) any small errors dont show up at all with a centerfire unless you're using the optics BC for DOPE out to 500+ yards.

However, I did use a Zulus v1 on a .177 sub 12 and found that, whilst you had to be insanely precise on the velocity and BC, the scopes BC DOPE was correct with real data and with real world use out to 85 yards.

 

[Smellydog]

I've had to adjust velocity to get the trajectory close to ideal with my 222.

Bear in mind even the slightest if inclination fore and aft will throw things out.
So if you shim as I did to get more centered before final zeroing or have a slight inclination of the action or an inclined mount it's going to throw the poi out slightly.

 

[12gsnapcaps]

I've had to adjust velocity to get the trajectory close to ideal with my 222.

Bear in mind even the slightest if inclination fore and aft will throw things out.
So if you shim as I did to get more centered before final zeroing or have a slight inclination of the action or an inclined mount it's going to throw the poi out slightly.

0 MOA rail and 0MOA mount on my setup.

I'll check the scope Gyro is calibrated correctly. That's one thing I haven't done, although I have no evidence to suggest the previous gyro calibration has been corrupted.

 

[f911swk]

sk std will have a variation of 70 fps,which is one of the disadvantages of 0,22r.

a ballistic calculation scope doesnt allow for that

 

[12gsnapcaps]

sk std will have a variation of 70 fps,which is one of the disadvantages of 0,22r.

a ballistic calculation scope doesnt allow for that

I chronographed a 10 shot string and I had a SD of roughly 10 fps, and produces exceedingly few fliers.

The high POI presents as a uniform group, not just flyers.

CCI Standard groups well, but had a SD of 50 and quite a few flyers, hence why I chose the SK Standard Plus.

So whilst I appreciate your comment, that's not correct.

 

[f911swk]

its correct for me,
i have the mtr version with the 520 and 0.22lr is not consistent enough at 100mt
even with rifle match which has a 60 fps variation

fac air with a sd of 3fps and a spread of 8fps is far more accurate and consistent

 

[12gsnapcaps]

its correct for me,
i have the mtr version with the 520 and 0.22lr is not consistent enough at 100mt
even with rifle match which has a 60 fps variation

fac air with a sd of 3fps and a spread of 8fps is far more accurate and consistent

Odd that it produces such a large SD for you - Perhaps a headspace issue or a bad batch?

All part of the fun of shooting I suppose - the tinkering and testing

 

[Smellydog]

Light firing pin strikes can increase velocity variation.

 

[f911swk]

if your ammo is consistent enough,i find this allows a bit of fine tuning

 

[Hollowlegs]

I have a cz 457 in 22LR running SK Standard Plus at 1070fps.

The DNT Zulus v2 in 3-12 is spot on, I have this one and a v1 and love them.

I'm printing thumb nail sized groups at 100 yards so accuracy is not an issue.

However, I've noticed the ballistic calculator makes my shots about 3-4 inches high at 100 yards.

This is with inputting the correct information, which I've triple checked. Speed of 1070, G1 BC of 0.14, Scope height (centre to centre) of 6.1cm etc. Speed has been triple checked with a chrono, HOB checked with calipers. All other info like bullet length and altitude etc, although mostly irrelevant, are all inputted correctly.

Only way I can get the projected aimpoint to match with actual POI is to change the velocity in the optic BC to an incorrect value of 1130 fps. - This gets everything to match up to 114 yards, however I'm not able to test further than this distance. Changing the BC value in the optic BC had no effect, even pushing the BC up to G1 0.20 - Only the faux velocity increase had an impact.

Not had this with any other calibre, only with .22LR - very strange

Anyone else encountered this? Which this scope or any other digital optic?

Very common, lots of YouTube videos on this

 

[12gsnapcaps]

Very common, lots of YouTube videos on this

Presuming you mean specific to my quandary and not just generic videos on setting up the scope/BC, Could you share one with me? I searched quite abit but couldn't find any.

 

[12gsnapcaps]

if your ammo is consistent enough,i find this allows a bit of fine tuning

View attachment 482214

I found tuning the BC made little to no effect, thus having to increase the velocity from the truthful (1070) to the incorrect (1130) to get the scopes BC Dope to intersect with the real world POI

 

[Hollowlegs]

Presuming you mean specific to my quandary and not just generic videos on setting up the scope/BC, Could you share one with me? I searched quite abit but couldn't find any.

I think it’s a very common issue, once your zero distance is set any adjustment required further than your zero distance you change either BC or velocity, below the zero distance you change the scope height of I have understood your issue? Are you on the AirGun forum? Stacks of threads and knowledge on them