IS THERE A FORMULA OR SOFTWARE FOR CALCULATING 1ST ZERO?

[badsworth]

Is there a formula for calculating 1st zero (the closest point where the bullet trajectory crosses the line of sight through the scope). I have tried various bits of software and the precision at the lower end of the range scale (20-45 yards) is rather lacking. For instance 'Pointblank' seems to tell me that for my optimum .223 home load zeroed @ 200 yards with a 1.5" scope height, the bullet also achieves zero at 35 yards - but the scale is so approximate that it could be 34 or 36 yards. I thought I would like to calculate it mathematically (but if anyone can recommend some software that does the maths - that would be OK too).

 

 

Can anyone help?

 

 

 

Badsworth

[Andrew]

Considering rifle weight, angle of departure, and other issues (including variances of actual performance compared to listed loading data) would make such a calculation hit or miss, at best. There is no substitute for doing the range work. ~Andrew

[kent]

Is there a formula for calculating 1st zero (the closest point where the bullet trajectory crosses the line of sight through the scope). I have tried various bits of software and the precision at the lower end of the range scale (20-45 yards) is rather lacking. For instance 'Pointblank' seems to tell me that for my optimum .223 home load zeroed @ 200 yards with a 1.5" scope height, the bullet also achieves zero at 35 yards - but the scale is so approximate that it could be 34 or 36 yards. I thought I would like to calculate it mathematically (but if anyone can recommend some software that does the maths - that would be OK too).

 

 

Can anyone help?

 

 

 

Badsworth

 

Thing is you could not descern the difference as 34 yds and 36 yds will seem like the same, indeed at the 20 yds to 45 yds it isn't going to make a heap of difference for most things you might shoot at. Balistic softwear will only take you so far to complete a dope data that tight you would always have to shoot each range

[Laurie]

The only way I can think of is to use a good ballistics program that accepts small range increments - Sierra's Infinity 6 allows single yard increments. Trying it with the old Sierra 155 MK at 2,850 fps and scope at 1.6" above the bore line with a 100 yd zero showed zero elevation at 69 and 100 yards as an example. You would have to be precise on the scope height for it to work properly. Tell me your load details and ballistics, zero range and difference between scope and bore axes and I'll run it for you.

[1967spud]

The only way I can think of is to use a good ballistics program that accepts small range increments - Sierra's Infinity 6 allows single yard increments. Trying it with the old Sierra 155 MK at 2,850 fps and scope at 1.6" above the bore line with a 100 yd zero showed zero elevation at 69 and 100 yards as an example. You would have to be precise on the scope height for it to work properly. Tell me your load details and ballistics, zero range and difference between scope and bore axes and I'll run it for you.

only thing is Laurie how can you garantee where the scope is pointing in the first place to get it pointing at the first shot before its shot ( if you see what i mean)

 

 

i think the best way is either by using a colimater or bore sighting at 25 or 50 then getting on paper from there

[Laurie]

i think the best way is either by using a colimater or bore sighting at 25 or 50 then getting on paper from there

 

Spud,

 

I agree. But I think the OP was asking about calculating '1st zero' on the assumption you already have your '2nd zero' sorted. That is 1st zero being the distance at which the bullet no longer flies below the sight-line, crosses through it to climb higher and eventually reach the highest point on the trajectory graph before dropping down again to coincide for a second time with the sight-line. The second zero is normally referred to simply as the zero for that rifle / scope mounting / load. You can't do anything accurately unless the (second) zero has been established first off.

 

Incidentally, Infinity 6 also has a useful Maximum Point Blank Range calculator. You input the diameter of the 'kill zone' on the 'target', scope height and load ballistics and it'll tell you the MPBR + optimum sight-in distance. So, say a deer has a 4" Kill zone, your load shoots around 1" 100yd groups, so reduce that kill zone to 3" and let's stick the 155gn SMK at 2,850 fps back in. (Yes I know you don't use SMKs on deer, but this is fantasy ballistics!) MPBR is calculated at 221yd on a 191yd zero - that is the bullet is always within 1.5" (half the kill zone dia) of the sight-line, initially below it then after 1st zero above it out to 220yd or so. As it's a bit unhandy to measure 191 yards out to zero the rifle in, look at the results table to see where the bullet strike is plotted for 100 or 200yd (or whatever suits) and it shows + 1.5" for 100, - 0.4" at 200yd, so zero the rifle to hit a target high / low as indicated at the appropriate distance.

[1967spud]

Spud,

 

I agree. But I think the OP was asking about calculating '1st zero' on the assumption you already have your '2nd zero' sorted. That is 1st zero being the distance at which the bullet no longer flies below the sight-line, crosses through it to climb higher and eventually reach the highest point on the trajectory graph before dropping down again to coincide for a second time with the sight-line. The second zero is normally referred to simply as the zero for that rifle / scope mounting / load. You can't do anything accurately unless the (second) zero has been established first off.

 

Incidentally, Infinity 6 also has a useful Maximum Point Blank Range calculator. You input the diameter of the 'kill zone' on the 'target', scope height and load ballistics and it'll tell you the MPBR + optimum sight-in distance. So, say a deer has a 4" Kill zone, your load shoots around 1" 100yd groups, so reduce that kill zone to 3" and let's stick the 155gn SMK at 2,850 fps back in. (Yes I know you don't use SMKs on deer, but this is fantasy ballistics!) MPBR is calculated at 221yd on a 191yd zero - that is the bullet is always within 1.5" (half the kill zone dia) of the sight-line, initially below it then after 1st zero above it out to 220yd or so. As it's a bit unhandy to measure 191 yards out to zero the rifle in, look at the results table to see where the bullet strike is plotted for 100 or 200yd (or whatever suits) and it shows + 1.5" for 100, - 0.4" at 200yd, so zero the rifle to hit a target high / low as indicated at the appropriate distance.

 

im with you now Vince thanks for clearing that up for me.

 

 

note to self - must read posts more carefully

[Laurie]

note to self - must read posts more carefully

 

Definitely - especially as it's Laurie not Vince and I'm an adopted white rose (Yorks) bearer and he's of the dreaded red rose (Lancashire) persuasion. (I won't take it as insult though, honest! I can't anyway as he'd ban me from Diggle, even though the ranges were in West Yorkshire until Ted Heath or whoever mucked up all the county boundaries back when I was a young man.)

[1967spud]

Definitely - especially as it's Laurie not Vince and I'm an adopted white rose (Yorks) bearer and he's of the dreaded red rose (Lancashire) persuasion. (I won't take it as insult though, honest! I can't anyway as he'd ban me from Diggle, even though the ranges were in West Yorkshire until Ted Heath or whoever mucked up all the county boundaries back when I was a young man.)

 

sorry Laurie im bloody losing it.

[Chris-NZ]

.. There is no substitute for doing the range work. ~Andrew

 

 

+1 on that from experience Andrew.

 

I leave a small plywood board on a fence (~28yds away) from our main benchrest and fire a sighter or two at it if there's a newly mounted scope. It assures you're always on paper at the proper sight-in range.

 

Chris-NZ

[Laurie]

+1 on that from experience Andrew.

 

I leave a small plywood board on a fence (~28yds away) from our main benchrest and fire a sighter or two at it if there's a newly mounted scope. It assures you're always on paper at the proper sight-in range.

 

Chris-NZ

 

 

Andrew, Chris,

 

you're also responding as if the question is about sighting a scope in which it isn't. Being 'on the paper' is about adjusting the sights to get the second zero where you want it - the point at which the line of sight (ie the straight line from the scope's objective lens to the point the reticle is centred upon) and the bullet's path coincide. But ..... before you get there, the bullet (1) starts out from the muzzle below the line of sight (because the scope is mounted significantly higher than the bore axis), (2) passes through the line of sight once (1st zero), (3) reaches its maximum trajectory, (4) starts to fall as gravity pulls the bullet downwards towards Planet Earth, and (5) finally crosses the line of sight again at the point of aim (but only if the scope has been correctly zeroed and the rifle is capable of precision shooting).

 

In the example I gave, the calculated 1st zero is at 69 yards from the muzzle. It has taken that distance to climb the 1.6" that the bore centreline is below the centre of the scope tube. It then rises marginally above the line of sight - really marginally because this is a 100yd shot with a ballistically efficient bullet and the highest part of the trajectory is a mere 0.06" above the line of sight, calculated as covering the 81 to 88 yards section of the trip before dropping gradually to intersect with the line of sight again at the 100yd (second) zero point.

 

You could establish this pattern experimentally by as you put it 'doing the range work', but it would be very difficult and tedious as it would require you to clamp the rifle into a really rigid rest and sight in at 100yd, then place an identical intermediate target mounted at an identical height to the original between the muzzle and main target, taking a shot without disturbing the original aim at all, seeing where the bullet struck the intermediate target in relation to its centre, and repeat this exercise moving the intermediate target away from the muzzle in small steps until the bullet hole coincides with its centre, then measuring the distance from the muzzle to the intermediate target. Presumably some method like this was originally used by the military to draw trajectories and provide the input to the maths that Ingalls tables and similar were based on, and which our PC programs still rely on today.

[Chris-NZ]

Laurie-

 

Fully understood all that as well as the original question.

I assumed the only value in knowing the figure is in "sighting in". Rather hard to miss varmints at 20-30yds..

 

There is a real danger in using very short range zeroing as errors quickly multiply at longer ranges. I know many guys are limited to shorter ranges but I never use less than 100yd for big game hunting and at least check at 200 for serious paper/varmint work, preferably 300yds.

 

cheers

Chris-NZ

[Laurie]

I assumed the only value in knowing the figure is in "sighting in". Rather hard to miss varmints at 20-30yds..

 

Well ... that's not what the OP asked. Personally, I'm a bit puzzled as to why anybody would want to know the distance to 'first zero', but presumably he has a reason.

[Laurie]

There is a real danger in using very short range zeroing as errors quickly multiply at longer ranges.

 

Chris,

 

rereading your post made me smile. This is exactly what the British Army does (and I suspect most other armies too). You see squaddies 'zeroing' their SA80s on the 30M ranges using a special target. I absolutely agree about the dangers in doing this. It may partly explain why a group of us watching a 'Territorial' infantry unit about to be shipped out to the Balkans into a shooting war some years back appeared to be unable to hit a human torso size target (Fig 11) at 200yd with optically sighted 5.56mm rifles. They were undergoing rifle training at Strensall near York shooting on an ETR range at Fig 11s set for 5-sec exposures and would drop if hit.

 

Despite a full firing line of camo clad guys - at least 10, maybe 12 or more, the best and very occasional hit rate was 5. 2 or 3 was more common, and zero hits were achieved in about every third or fourth cycle. I'm only glad the Fig 11s weren't shooting back like the real opposition - but then maybe their AKs are equally badly zeroed!

[brown dog]

This is exactly what the British Army does (and I suspect most other armies too). You see squaddies 'zeroing' their SA80s on the 30M ranges using a special target. I absolutely agree about the dangers in doing this. It may partly explain why a group of us watching a 'Territorial' infantry unit about to be shipped out to the Balkans into a shooting war some years back appeared to be unable to hit a human torso size target (Fig 11) at 200yd with optically sighted 5.56mm rifles.

 

Not strictly correct Laurie. The Army zeroes at 100m. Battle zero is often checked at 25m in pipe ranges - and that's a function of space and time; not perfection.

There's a key word in your story that explains what you may have seen (starts with a 'T' )

[Laurie]

Not strictly correct Laurie. The Army zeroes at 100m. Battle zero is often checked at 25m in pipe ranges - and that's a function of space and time; not perfection.

There's a key word in your story that explains what you may have seen (starts with a 'T' )

 

 

Quite agree - little trigger time = crap shooting! The Terries seem to zero their rifles at 30m on Strensall as a matter of course in recent years before heading out for the main ranges.

 

(It'll be interesting to see if the government's new found enthusiasm for reserve forces translates into proper funding, additional training and more generous equipment provision ..... or whether this is just another cynical cost-cutting exercise that lets them cut the Regulars further without filling the resulting gaps.)

[brown dog]

Quite agree - little trigger time = crap shooting! The Terries seem to zero their rifles at 30m on Strensall as a matter of course in recent years before heading out for the main ranges.

 

I think what you're seeing is a litigation proofing get-on-paper gross-error check, rather than a zero. If they're treating it as a zero, you've pinged the problem. I once spent 7 weeks on the board of a very sad Courts Martial relating to 'T' weapon handling. I'll bore you about it if we ever have a pint together

 

(It'll be interesting to see if the government's new found enthusiasm for reserve forces translates into proper funding, additional training and more generous equipment provision ..... or whether this is just another cynical cost-cutting exercise that lets them cut the Regulars further without filling the resulting gaps.)

100% the latter I think. Smoke and mirrors

As I always say, there's no point getting stressed about it; if the people of Britain only want to fund an equivalent of the Belgian Defence Force, that's fine.

They just need to then understand that it can only do what the Belgian Defence Force does.

Our generals, who've spent a career waiting to get to control the train set need to get their heads around that too - the train set isn't what they thought they were going to get; and they'll have to stop pretending it's what they feel was their right.

[Alycidon]

Zero your rifle to be about 3/8 inch (10mm) high at 100 yards, 1/2 inch (12.5mm) at max. That will give you a primary zero (second cross) at about 150/160. First cross will be about 60 yards. You will be able to take head shots out to 150 yards without thinking about it.

 

http://www.biggameinfo.com/BalCalc.aspx put your velocity and bullets co effocoent in and away you go. Its not dead on but not far off under 180 yards. Why are you interested in the first cross range?.

 

A

[forbie]

There is or was free software download from the net I think it was called point blank. Gave you increments and point blank range target to plot on scree for records etc best of all was free. its on the hunting nut web site