Bugger. It’s lifted its head up and started walking away, now, how far away is he, is that fifty meters? One hundred? Could be a bit more. I need to dial for elevation, wind, ah, no, no time, use the reticle, first dot, second, oh hell. It’s nearly in the bush, shit. Just wing it, I think it is over a hundred. Just hold a little high. Pull the trigger and hope for the best.
Less guessing, more certainty
While modern reticles, ballistic turrets and gadgets all make things a lot quicker and easier, things can still get a little hairy when you are hyperventilating as the biggest Stag of your life is starting to slowly walk back into the forest line. It’s not the time to start second-guessing yourself, and it certainly isn’t the time to start trying to remember how your ballistics chart related to your reticle marks.
It’s also certainly not the time to be taking a shot in the hopes that it will hit an animal and disable, hopefully, kill it. That is cruel, unethical, and just plain inhumane.
So, a method of maximising the setup of your hunting rifle, cartridge and scope to ensure you can point and shoot for the majority of your shooting makes sense. Unsurprisingly, such a methodology exists.
Understanding Maximum Point Blank Range.
Essentially, maximum point blank range is the range of distance where you can hold dead centre on a target and still hit it within a certain predefined distance up or down. Most commonly this is calculated to correlate with the ‘kill zone’ on the primary target species.
Consider it this way – imagine a rifle centred down a pipe, which has a diameter the size of the vital organs of your target (often said around 6 inches for the smaller deer)1. MPBR is the maximum distance you can hold dead centre on that animal and never hit the top or the bottom of that pipe over that distance.
So, how does this work? Well, first of all, remember that a projectiles tractory follows a parabolic curve. That is, the projectile (bullet) leaves the barrel heads up over the line of sight, then curves slowly back down to the zero distance. The photo above is a terribly exaggerated example, but it illustrates a point.
So, to then continue the example:
No, not my original diagrams – but then, I am going to just make up exactly the same thing, so might as well recycle.
In the second image – we can see that the path in the middle has a trajectory that doesn’t pass higher or lower than three inches from the line of sight. This continues further than where the actual rifle zero is set too.
So. This means that for every firearm system, there is an optimal zero that will allow us to set and forget the elevation and be comfortable that we are going to be within a ‘margin of error’ when we centre and pull that trigger.
What do we need to to know then?
One very important factor needs to be decided before we get too much further into calculations.
How big is my targets ‘kill zone’?
Ah. Good question. Obviously, the size to kill a rabbit is way different to a Wapiti. So, part of this process is deciding how big to calculate the kill zone for. Now, within this sizing, we also need to account for the accuracy of the rifle and of the shooter.
If it’s a Red, let say the boiler room is going to be about 220mm. To that you need to add some leeway for that simple fact you can’t put every single shot on top of each other – certainly not off hand, while short of breath having just climbed over a ridge and spotted a deer (be realistic).
If you shoot necks, it’s less, heads, even less (how about we just rule out headshots for rushed shooting altogether aye lads?).
All in all, I would personally allow something like 150mm – that will cover everything down to fallow size and ensure good shot placement on all the deer.
So, we have our maximum allowable spread distance. Now we also need to know something about the ballistics of the gun we are shooting.
At a bare minimum, the box of ammo you shoot should have enough details – realistically, I would expect you to have also run your rifle over a chronograph with the ammo you are planning on shooting a live animal with, because again, we are humane, ethical hunters and do all we can do to ensure a clean kill.
Finally, some basic details of the rifle, in particular, the sights are needed.
Let’s take my Rem700 in .308 – not that I would hunt with it – but I happen to have the load data handy.
It shoots a Lapua 155 Scenar at 899mps (that’s 2949 fps). Chrono is a Magnetospeed. Sight height is 5cm above bore.
I pop over here – http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi – and start entering things in.
You don’t need to enter everything. Projectile, velocity, sight height, vital zone radius is all you really need. Remember to check ‘Zero at Max. Point Blank Range’ – then hit calculate.
The results will give you all the information you need to setup the MPBR on your rifle. In my case – I get the below:
So, if I set my zero at 233 meters then that means I can shoot an animal anywhere out to 272 meters, and still hit within 75mm of my point of aim. At, at the maximum distance, I still am going to have nearly 2000fps of energy – so plenty to put the animal down.
Then what? How do I set a Zero?
Easy. Go back to our online calculator, uncheck ‘Zero at Max. point blank range’ then zero the rifle at 100 and use the drop chart! Looking at my example – I will zero to 100, then give myself 7 clicks up (my pick between the 225 and 250 ranges). This means, if I want to take the time and actually dial up a distance, I can still work from a known 100 zero. If you wanted, you could just use the dial up’s and downs from the original chart – or rezero the scope after adjusting – whatever is going to make the most logical sense to you. You don’t want to have to be second-guessing yourself when faffing with scope dials.
Who can the MPBR system work for?
If you are a hunter that does a mix of bush stalking, into clearings, up into tops and back down again, the having your rifle set up this way may be of benefit. If you don’t want to have to mess with the scope before pulling the trigger and have multiple distances to contend with, then the system will let you set and forget, in the understanding that you will not be able to get the pinpoint accuracy dialling it would.
If you are primarily a bush hunter, then pulling that zero back down to where you shoot might make more sense – it would allow for closer, more ‘picked’ shots where you need to round to go exactly where you aim it. For the mountain ‘long-range’ hunter – then you are going to have the time to figure out an exact ballistic solution and setup for the shot.
So – the MPBR setup isn’t for everyone. But for a lot of hunters, it provides a simplified method of having the rifle set up to hit the animal without having to do too much mental calculations in the field.
150mm for us metric folk ↩