Inch high at 100 Yards… and MPBR…
What’s the best way to zero your rifle..?
It seems that one of the common recurring question across shooting forums and social media is “What range do you zero your rifle at?”
And one of the popular answers is “an inch high at 100 yards”.
I’ve seen many responses to this along the lines of “that sounds complicated” and “why bother? I just zero dead on at 100”.
The fact is, an inch high at 100 is a simple way of giving you greater range at which you can shoot without having to worry about hold-over – meaning you can “point and shoot” out to greater range.
But you can go better than that… and that’s setting up your rifle to adhere to the concept of MPBR – Maximum Point Blank Range.
(And contrary to what they say in the films, Point Blank Range isn’t putting the muzzle right up against the target and squeezing the trigger.)
By definition, Maximum Point Blank Range is the range over which you can shoot where your bullet doesn’t go above or below your horizontal crosshair by more than a determined amount.
In order to understand MPBR further, there’s a few things that we need to consider – as follows:
- What actually happens to a bullet when it leaves the barrel of your rifle..?
- Rifle set up – the relationship between your scope and your barrel.
- Why MPBR is the most effective method for zeroing your rifle.
What happens when a bullet leaves the barrel of your rifle..?
First off, it’s worth explaining what happens when a bullet exits the end of your barrel. Two facts of interest are as follows:
- Bullets don’t fly – they “drop like stones”
- If you were to drop a bullet from the height of your chamber at same time as firing a round from your rifle, the two bullets would hit the ground at the same time – one by your feet, the other several hundred yards down range.
So the key message here is bullets don’t fly – they just fall. Some are more stable than others, some are more aerodynamic than others – but they all fall the moment they leave your barrel.
Rifle set up – the relationship between your scope and your barrel.
In order for you to zero your rifle, your scope must be angled towards the bore of your rifle. This is such a slight angle that you won’t see it with the naked eye – but without this angle the path of your bullet (its trajectory) would never converge with the line of sight of the scope (light travels in straight lines – and remember, bullets fall/drop)
So… imagine you’re bench rested and the line of sight of your scope is 100% parallel with the ground. Based on what we’ve established, if your barrel was parallel to your scope – and the bullet is dropping the second it leaves your barrel, then the bullet will never cross the line of sight – so your point of impact will never be at the intersection of your crosshairs.
In order to get your bullet to cross the line of sight of your scope, then the barrel needs to be angled up towards your scope. So you are actually shooting upwards towards the line of sight.
Make sense so far..?
Why MPBR is the most effective method for zeroing your rifle.
So I’ve been telling you that by using MPBR you can extend the range at which you can “point and shoot” without worrying about holdover – the following three examples will show you why that is the case…
The examples we’ll examine are:
1. Dead on at 100
2. Inch High at 100
3. Adhering to MPBR
1. Dead on at 100 Yards
What happens if you zero at 100 yards…
The following example is a 40gn VMax with a muzzle velocity of 3500fps.
Zeroing at 100 yards results in the bullet trajectory never going higher than the line of sight of your scope and at 200 yards, the bullet will be 2.28 inches low.
This is fine if all you ever do is shoot things out to 160-180 yards. Anything past that and you’re going to have to compensate with hold over to allow for bullet drop.
2. 1” High at 100 Yards
So what happens if you set your zero to 1” high at 100 yards
In this example, the bullets trajectory crosses the line of sight at 47.5 yards, is 1” high at 100 yards, and at 200 yards, its just quarter of an inch below your cross hairs.
In fact, from 20 yards to 220 yards, the bullet is never more than 1 inch above or below the cross hairs.
Clearly that’s a major advantage as for anything you’re shooting within that range, you don’t need to hold over or under to for your bullet to strike within a 2” vertical spread.
3. Zeroing to achieve Maximum Point Blank Range
Taking this a step further, we get to MPBR – Maximum Point Blank Range…
By definition, Point Blank Range is the range over which you can shoot where your bullet doesn’t go above or below your horizontal crosshair by more than a determined amount.
One way to explain this it is to imagine you are shooting into a pipe. The diameter of the pipe is the size of the kill zone of your target… The MPBR is the furthest distance that you can shoot so that the bullet touches neither the top nor the bottom of the pipe.
For the sake of this post, lets decide that the kill zone for a fox is 3” – we therefore want to work out the best zero so that our bullets POI is never more, or less than 1.5” from the horizontal crosshair.
Using a calculator such as the one found at Shooterscalculator.com you can work out the theoretical MPBR for your set up. You’ll need some facts before you can run the calculation though, including:
• Muzzle velocity
• Ballistic Coeficient of bullet
• Scope Height
• Size of Kill Zone
The green tinted band represents the Kill Zone of 3”.
As you’ll see from the above graphic, with the rifle set up as above the Point of Impact (POI) is as follows:
- 1.5” LOW – 5 yards
- DEAD ON – 43 yards
- 1.3” HIGH – 100 Yards
- 1.5” High – 130 Yards
- DEAD ON – 210 Yards
- 1.5” LOW – 241 Yards
Using the PBR and MPBR terminology with this example, your Point Blank Range is 5-241 yards – and your Maximum Point Blank Range is 241 Yards.
Hopefully that all made sense – and you can see the advantage of using MPBR to determine the best zero to get the most from your rifle.
In short, understanding and utilising the concept of MPBR allows you to zero your rifle to give you the maximum possible range over which you can “point and shoot” without having to worry about hold over / under.
Looking back at the three examples given, the range where the bullet remains within a 3” kill zone is as follows:
Chairgun from Hawke – whilst originally designed for Airgun use, you can use this free app to plot your trajectories and calculate MPBR
Shooters Calculator – another great app for working out MPBR.