Thread: Ballistic truing conundrum

Been playing with loads for 284 & 7SAUM using RL26 with 162 ELDMs and 165 Norma BondStrike. Long story short ended up with some nice tight groups (0.5 - 0.6 moa) and velocities around 3000 fps. Both 284 & SAUM are 22in barrels. The 284 running 3010fps with 162 AMAX & SAUM 2995fps with 162 ELDMs. Interesting and in line with early load dev with different powders, get more speed with the 284, and in this case (RL26) less powder.
Anyhooow, then ran some shots with the SAUM past couple of calm days with 162 ELDMs at 625 yards to validate speeds & drops. Using Hornady bc calculator & Kestrel 5700 both gave me 10moa or there abouts as the come up. But shots were consistently high going over top of 10in gong, and after close inspection of target area & some rough maths estimated that 9 moa should be on the money. So back to shooting position, dialed 9.0 moa come up & confirmed POA and POI were bang on (within 1 inch).
Scope (VX6) is zeroed for 200 yards, 1.3in high at 100.
Never came across a case before where dial up needs to be reduced significantly???
Most times if scopes don’t dial true moa, they dial less - like IPHY or in some cases less. Leupy scopes in my experience tend to dial IPHY or slightly more.
If you follow the truing logic of correcting muzzle velocities to account for drop, then to get 9.0 moa come up you’d expect muzzle velocity of ~3100 fps. No way can I see that out of SAUM & 22in bbl. Similarly can’t imagine BC differences explaining 10% change 10 to 9moa??

Any of you LR experts out there have any thoughts or ideas to explain this mystery?

Have you proved the scopes adjustments on paper at 100m ?

No, have to do that but I’ve never come across a VX6 that dials more than true moa. Let alone 10% more?!
But it’s the only thing that seems to fit the observed facts.

What about air pressure ? Altitude can affect it a lot ( weather, not so much) and it just changes the apparent BC in proportion .

We are about 80m above sea level, pressure according to weather maps past few days is 1015 - 1020 hPa. Can’t see that changing anything much. Also any air pressure factors should be covered with ballistics calc from the Kestrel 5700.

Originally Posted by chainsaw

We are about 80m above sea level, pressure according to weather maps past few days is 1015 - 1020 hPa. Can’t see that changing anything much. Also any air pressure factors should be covered with ballistics calc from the Kestrel 5700.

Good chance you zero not perfect at 200.
Best practice is 100m or yard zero as yocan really get it perfect .
If your zero is perfect trust the app doing the validation in the kestrel
Honestly watch Tod hodnet's videos on truing he really knows his shit.
1.3 inches seems quite low for above bore height to.
I do heaps of validation shooting and in your case I'm picking its something simple.


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The “1.3in” above is the height of POI (centre of grp) above POA at 100 yards. I checked this at the range a week ago. I agree it might not be exactly zero at 200, but it’s within a gnats whisker. The scope height is 1.6in and I used that input to Ballistic calcs.

Originally Posted by chainsaw

The “1.3in” above is the height of POI (centre of grp) above POA at 100 yards. I checked this at the range a week ago. I agree it might not be exactly zero at 200, but it’s within a gnats whisker. The scope height is 1.6in and I used that input to Ballistic calcs.

OK, as I say I'm doing this all the time.
Make your point of impact smack on at 100 then validate from that.
If you want a 200 zero just leave your scope set on that.
I can guarantee this works otherwise you will out clever yourself!
If you have a kestrel 5700 you have the best ballistic solver on the market.
I'm using mine daily and it's never wrong as long as you put the right info in

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Re zero at 200. The further out you zero the more error you can induce. Make sure it's exactly 200m. Or is it yards? That could cock it up.
Check atmospherics are correct, scope height etc. It all needs to be as close to perfect as you can get it if your going through a trying process.
625 is also on the close side for trying. 800m is usually the standard.
How good is your shooting? We're you shooting in a position or off something that the rifle could jump slightly higher? Carbon bipod on rocks or something? Or jambing the rifle down into the ground to get elevation?
It's not very hard to induce 1moa of shift, I've seen a lot more.

What's the objective in asking?
To me I'd call this "dope" and get on with my day... but i spose if you want to dial in a computer thingy then yeah... you need to work out the whyfor.

Originally Posted by 11mms

What's the objective in asking?
To me I'd call this "dope" and get on with my day... but i spose if you want to dial in a computer thingy then yeah... you need to work out the whyfor.

There is nothing worse when taking a shot and doubting you accuracy.
Nothing better than taking a shot when you know you've done every thing perfectly!
Man I have seen some shit zeroed rifles and they wonder why they can't hit any thing.

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Originally Posted by andyanimal31

There is nothing worse when taking a shot and doubting you accuracy.
Nothing better than taking a shot when you know you've done every thing perfectly!

Yeah but my point was, now he knows... 10 clicks, on his scope, with his load, from his gun, at 625 = whatever.
Regardless of what any app says... I'll always verify POI through all ranges I want to shoot.

Originally Posted by andyanimal31

OK, as I say I'm doing this all the time.
Make your point of impact smack on at 100 then validate from that.
If you want a 200 zero just leave your scope set on that.
I can guarantee this works otherwise you will out clever yourself!
If you have a kestrel 5700 you have the best ballistic solver on the market.
I'm using mine daily and it's never wrong as long as you put the right info in

Sent from my SM-A226B using Tapatalk

Yes, the Kestrel 5700 is a wonderful bit of kit. I don’t doubt it for a second, but also use the Hornady BC calculator as cross check when something like this happens.
I do the scope zeroing at 100 yards, just set to get the POI 1.3in high = 200 yd zero.

Had exactly the same issue with my 284 and the LRABs. Never figured it out. Ended up fudging the figures to make it all line up and validated out to 900 and just went with it. Then one day the barrel decided it didn't like the accubonds any more courtesy of fire racking around the throat and some pitting halfway down the tube.

Originally Posted by Skirch

Re zero at 200. The further out you zero the more error you can induce. Make sure it's exactly 200m. Or is it yards? That could cock it up.
Check atmospherics are correct, scope height etc. It all needs to be as close to perfect as you can get it if your going through a trying process.
625 is also on the close side for trying. 800m is usually the standard.
How good is your shooting? We're you shooting in a position or off something that the rifle could jump slightly higher? Carbon bipod on rocks or something? Or jambing the rifle down into the ground to get elevation?
It's not very hard to induce 1moa of shift, I've seen a lot more.

Zeroing done at 100 yards, see other post below. I never use metres, all measurements are inches, yards, moa, etc.
The 200 zero might be 205 or 195, but that makes naff all difference - maybe 0.1 or 0.2 moa at 625yrd. Not a cause for 1moa delta.

Atmospherics etc, covered by Kestrel. Again any small change or error is going to be sfa.

Yes ideally I’d do truing at longer range but 625yd is the max I have access to.

How good is the shooter? Good point. Good enough to consistently shoot 1/2 moa grps in light weight (6lb bare rifle) hunting rifles.

Shooting position- a bit average. After this shit wet winter the cattle have munted the paddocks good and proper. So finding a spot with out too many lumps and bumps not easy. Bipod (Spartan) had good lock up and stable forward load plus rear bag allowing a fairly solid platform.
Shots on gong poi was within 1in of POA so despite a less than ideal ground conditions I feel the results validate the accuracy.

My next step is to calibrate the scope dial up on paper at 100 yards.
As mentioned at start of thread have never seen a Leupy dial more than true moa. But maybe this is an exception?