One range trip, two rifles, a stack of questions.

If you want a 300 meter zero with an AR type rifle using 55gr bullets in a milspec load, zero your rifle at 17 meters. The bullet will hit the target as it rises, be above the line of sight from then on until 300 meters. You could also zero 0.7 inches high at 25 meters, or 2.5 inches high at 50 meters.

With a 300 meter zero your bullet will have a maximum ordnate of 6.9 inches above line of sight around 170 meters.

Hope this helps.

Jimro
 
Mr Pond,Perhaps you are unaware,but if you go here:

http://www.hornady.com/ballistics-resource/ballistics-calculator

Hornady will happily let you use the calculator,too!

Your .223 will have a lower ballistic coefficient than your .308....given the ammo you are shooting.That means the .223 bullets will lose velocity quicker.

That's why they are hitting lower.

Play with the calculator,and decide what you want in a trajectory/zero.The close up zeros,like 25 or 50 yds,IMO,are useful to get on paper,but I always fine tune at the longer range.You get to decide how much mid range trajectory you want on top of your line of sight.If you want a 300 yd zero,try about 4.5 in high at 100,and 5.5 in high at 200.Myself,I can work with that,I just hold low at 100and 200.The .55 gr bullet has a BC of only about .265.A 69 to 75 gr bullet will retain velocity better.If you want to shoot at 300,I'd try those.You will lose some initial velocity,so the 300 yd trajectory will be similar,but wind effect will be less,and it will make more difference at longer range.

If your .223 ammo is commercial Mil-spec,that will contribute to larger groups.its not known for precision.

Your rifle has a free floated barrel,yes?I forget .If it does,even with a chrome barrel,I would expect even a mediocre "lemon" to shoot insde 3 MOA at 300 meters,or 10 in.Actually,with good handloads,or match to varmint grade ammo,and a quality free floated rifle ,I'd be surprised if the rifle would not shoot better than 2 MOA at 300.I would not be surprised if it shot closer to 1 MOA.
 
My concern did not rise from comparing .308 to .223. I just happened to want to shoot both rifles.

The problem was that my .223 dropped 14" or so over 300m. That seemed quite high based on my expectations and resources such as the presentation I linked earlier led me to believe that was abnormal.

It seems more likely that the results are a combination of how far I zeroed my scope, the ammo's own BC and quality, and my shooting abilities.

I now need to redo my zero, trying to get a near zero at 300, on the bullet's return from the apex. This should give me an initial zero between 15-40m or so and a mid flight apex somewhere about 150m, according to earlier posts.

If all goes well, I will be able to aim dead on at any distance from 25-300m and have hits in the Alpha zone of a IPSC target.

Whatever the causes, I am sure that any of the experienced shooters from TLF would produce far better groups with my gun, than I have. That much is clear.
 
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Pond, James Pond,

The original US military M193 load was designed to have a 250 meter battlesight zero. And so it was easy to zero the rifle at 25 meters with the 55gr load at 3,200 fps.

Your Sig has a shorter barrel, so velocity is reduced, and you are looking to shoot to 300 meters instead of 250. That means your "near zero" must be closer than 25 meters.

You can figure it out easily by using a ballistics calculator, I generally just use JBM unless I'm away from the internet then I'll use Strelok on my phone. Choose the 55gr FMJ bullet, I use Winchesters, and input the velocity you get from your Sig. Then calculate for a 300 meter zero, but set the incrementation to 1 meter instead of 100 meters. Scan down the resulting chart until you see 0.0 and not the range in meters. If you can't put a target at that specific range, just look for a range you can, like 25 or 50, and it will tell you the difference between Point of Aim and Point of Impact at that distance.

To get the max ordnate, simply continue to scan down the chart until you see the biggest number in inches, it will generally be just past halfway to your far zero distance.

Hope this helps.
Jimro
 
Thanks Jimro.

I have the same App on my phone, which I have used on occasion, but never like that. I'll have a go this afternoon. Then I will go to an indoor range here that has about 30-40m to play with and try to reset my zero.

If previous posted calculations prove right, that should be about 12 clicks "up"!!

Then I can go back to the 300m range and show it who's boss!!! :D
 
You know, perhaps I'm being unrealistic regarding what .223 can go. After all, it doesn't fire a laser beam, but a small, fast bullet.

Perhaps I should tell you lot what I want, and you can tell me if it is achievable.

I want to exploit the flat shooting nature that is commonly ascribed to .223. Right now, other than range practice, my AR is going to be used in IPSC competitions. Stages will include distances of under 10m, all the way to 300. However, beyond 25m, the increments are defined by the ranges that allow competitions, so one can expect the distances to be 25, 50, 100 and 300m.

I want a load that will allow me the greatest chance of hitting alphas, with the least amount of fooling about with hold-over etc, when aiming through my 1-4x Leupold.

So for a change, rather than me telling you what zero I want, why don't I ask you if it were your AR, what would you be setting it to?
 
The Alpha zone is 20cm at its widest point, and 31cm tall.

That translates to 7.8 inches wide, 12.2 inches tall if I did my math right.

If you want to have a no hold zero with a 55gr FMJ load at 3,130 fps muzzle velocity you have two choices.

Choice one, zero at 20 meters, you will be +5 inches at max ordinate and less than two inches low at 300 meters. This is a "5 inch pipe zero" where the bullet will never be more than 5 inches above or below line of sight out to 311 meters. With this option you can simply hold center of mass in the alpha zone and as long as you don't mess up the shot the bullet should land within the vertical confines of the alpha zone.

Choice two, zero at 25 meters, you will be +/- three inches out to 250 meters, and 7 inches low at 300. This means you adjust your aim point at the 300 meter targets to the top of the target to drop the bullets into the middle of the alpha zone and hold center mass for all other shots. This is a not a true "no holdover" zero, but will more precisely put shots in the alpha zone at all distances 250 meters and less.

I hope this helps.

Jimro
 
Jimro's got it. You use a ballistic calculator along with your IPSC parameters to determine how the rifle ought to be sighted in, so any shot within match guidelines will hit the Alpha.

Keep in mind, though, as that "pipe zero" grows, the alpha zone doesn't, so it's even more important for the shooter to be able to deliver the goods. Take that 5" pipe zero, for instance: If you were precisely zero'd on the IPSC A-zone with a 12" vertical spread, you, the shooter, could make a 6" error and still hit it. But if you're in a match and have to rely on the 5" pipe zero, your round can hit 2.5" closer to the edge of the A-zone with a dead center hold. IOW, as distance from zero increases, the "pipe zero" effectively makes the A-zone smaller by giving you less room for error, but the trade-off is that you don't have to mess with zeros.
 
Pond said:
You know, perhaps I'm being unrealistic regarding what .223 can go. After all, it doesn't fire a laser beam, but a small, fast bullet.

I want to exploit the flat shooting nature that is commonly ascribed to .223
Click to expand...

Everything in life is a balance and a compromise. You can get a flatter shooting round by going with a lighter, faster bullet, but it can leave you more susceptible to wind drift because the bullet's lighter, so wind will become your new headache. Maybe a worse one, since you can know what trajectory is, but wind is up to mother nature and tough to effectively gauge (especially with a timer running) as well.

I think .223 is a decent compromise for what you want. It's popular in IPSC, no? Ideally, you'd reload with heavier bullets that still retain a pretty flat trajectory and mild recoil, but your 55gr ammo ought to work ok too.
 
Jimro, it looks like your trajectory calcs are based on a 1.5" sight height, instead of the 2.5" common on AR's.
Pond, you'll have to figure in your sight height above bore.
 
Pond, you'll have to figure in your sight height above bore.
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I'll have to measure, but I expect about 2.5". It is 1.5" from scope centreline to receiver flat-top. So about another inch to the bore from there.

Perhaps it says in the manual how far the bore is below the rail.

Perhaps I'll try the 5" tube method to start with. If that proves too challenging, I can go to the 25m zero method and try that. I won't be competing for a little while right now.
 
I used the default because I didn't think to ask the exact height of the Leupold above the bore on Pond's Sig.

To illustrate the two previous options with just an added inch of height above bore:

If you push A 5" pipe zero to 2.5 inches you move the near zero to 31 meters, and are good to 318 meters.

If you push a 3" pipe zero to 2.5 inches above bore you move the zero to 39 meters, but are still 6.6 inches low at 300 meters.

But it brings up a good point on any rifle, if you do a near zero, you need to confirm the far zero at the real distance.

Jimro
 
A 10 inch diameter pipe has a 5 inch radius. I apologize if that was unclear, but +/- 5 inches off of line of sight is what is being measured with that type of zero.

Jimro
 
The simplest way to find your answers is determine the "PBR" (Point Blank Range) by using a ballistics calculator, filling in your load data, and then defining the diameter of the target so the bullet never rises nor falls more than half that distance from the LOS

http://www.shooterscalculator.com/point-blank-range.php

Here is an example: Let's say you are deer hunting. The vital zone of deer is roughly 8 inches. Using the calculator it tells you that you should zero your rifle at 250 yards and that the MPBR is 300 yards. That means that if you aim at the center of the vital zone of a deer at any range between 0 and 300 yards, you will hit the vital zone. This means that you do not need to worry about any bullet drop or holding over if the animal is within the MPBR.
Click to expand...
 
Although I understand what everyone is saying, it's all over my head.
But here's how I'll say it.
Most people don't realize a bullet rises before it drops.
I'm not a fan of the .223 or the AR but neither are bad. They are both however over exaggerated.
 
Most people don't realize a bullet rises before it drops.
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So a bullet leaving a horizontal barrel would rise before it falls?

Is this because of muzzle flip, or do you mean that barrels always point up a little to allow bullets to reach distant targets?

If not those, I don't understand how that is possible.
 
So a bullet leaving a horizontal barrel would rise before it falls?
Click to expand...

No, it never rises above the "line of bore"
It can rise above the "line of sight" IF the barrel is angled upwards
 
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