WHEN I ORIGINALLY WROTE THIS ARTICLE, I MANAGED TO TRANSPOSE SOME FIGURES, which, in hindsight, gave some seriously messed up results and caused me to draw some incorrect conclusions. I have updated the figures now, and corrected observations.
Doing a comparison requires quite a bit of framing and context. It’s important to remember this is all purely theoretical – mental masturbation at it’s best – and I am sure the wild west of the internet will be more than happy to pick it to bits.
I was interested to have a bit of a comparison of a few of the common cartridges out there, in order to see how they really stack up against each other on paper.
I often get asked – what’s the best cartridge for ‘x’ – x often being a vaguely construed idea of ‘long’ range hunting. Once you get a couple of question marks in a sentence, I start to get nervous.
Anyhow, I ran some numbers in Coldbore, and while most things were expected, there are a few interesting observations.
For the purposes of the comparison, I decided to use Hornady Precision Hunter as a base. They have a decent range of ammunition spanning most of the most common cartridge options available in factory rifles.
Factory ammo, factory rifles – sure, custom builds running hand loads are going to get different results. However, if you are already that far down the rabbit hole – there is also a good chance you have already run the numbers yourself. You may even be comparing different projectiles within the one calibre as well. I know of more than a couple of firearms that have been built from the projectile backwards – and ultimately, this is the best way. However, for us mear mortals still running factory rifles – this gives us a good base to work from.
I originally, and would normally compare everything in MILs – but considering who might be reading this, and the context of the intent – I decided to present them in CM measurements at distance. It makes it a bit easier to understand the real-world context of the figures.
Let’s start with the obvious – drop at distance.
Even at 200 meters – we can start seeing the difference between calibres. The drop on a .308 is nearly 10 centimetres more than the .270 or 300WSM. Now, I get it. We dial or hold for the drop, it’s a constant, etc, etc – but – that difference is enough to significantly alter your MPBR is you use a ‘walking zero’ and would also show up in wind deflection. Both drop and wind are reliant on accurate ranging or wind calls – both of which are fallible and ‘flatter/straighter’ shooting calibres1 gives us ‘more’ margin for error.
Yes, there is also the old wives tale that a .308 with buck bushes better – but we can debunk that in another article.
Now sure, gravity is a constant, and most ballistic calculators are able to give us pretty good solutions on the fly these days – but the other consideration is this – a flatter shooting bullet is going to give you a better margin for error when it comes to both rangefinding and shooting. If a round drops less it’s deviating less from point of aim – though this is maybe more relevant with the next chart. Windage deflection.
Winding on the windage
Here, again, the good’ol .308 is pushed around the most, with the 6.5 PRC, and it’s slippery bullet flying the truest. Interestingly, the 300WSM fares better than the 270 here – potentially due to the heavier projectile not being pushed2 as much as the light .270 pill.
A 10 mph wind is considered a ‘gentle breeze’ on the Beaufort Scale – so something plenty of us will be hunting and shooting in. In fact, it’s also more likely to be the big unknown for us. Many shooting to this distance will be utilising a rangefinder. If you are not, you seriously need to be questioning what you are actually up to. But even with a Wind Meter (like a Kestrel) – wind can be a challenge to read at the best of times.
I recently spent the afternoon on a bank with a client – we were shooting to 700 meters and ended up holding over 4 MOA of wind to hit centre mass. From where we were though, there were NO visible wind indicators. The wind was still, the tree tips not moving. Nothing. But the projectile was being pushed. A lot.
In the end, the conclusion was there was a decent wind funnelling through the valley we were shooting over – we couldn’t see the effect, because it was likely 100 meters or so above the ground – so didn’t push the foliage around at all. Shooting a round that was less likely to be ‘bucked’ by the wind is certainly more helpful in this situation.
Velocity and energy – terminal ballistic considerations
Hitting the animal is only the first (though very important) consideration. Even just hitting it isn’t really enough – a couple of centimetres can mean the difference between a ‘kill’ shot – that ensures a quick efficient death, and a gutshot, leg shot, or worse.
However, even assuming you hit a good, solid, well-placed hit, what happens then is still vitally important to the outcome of the hunt. What bullets do when they hit flesh is often referred to as their terminal ballistics – and a lot of thought also needs to go into how the projectile of choice will perform at this point.
The evolution of projectile design is what allows us to do a lot of what we do. Originally, the main things we had to work with were mass and velocity – heavy projectiles moving fast – hence the rise of families of cartridges like the Weatherbys. However, with modern knowledge and design, we are able to start at maximising efficiency in both BC, or ballistic coefficient (how the bullet flys) and expansion capacity (what happens when it hits something).
Ideally, we want a bullet to transfer all it’s remaining kinetic energy into the target when it hits. This will generally result in the most efficient killing power. One primary way that a bullet can do this, is through expansion – expansion is the opening up of the round during impact – think of it as putting on the air brakes while passing through the animal. This process opens up the surface area of the projectile, thus braking the velocity more inside the wound channel – and the transfer of energy into the animal is maximised. It’s often suggested that the perfect round would dump all the kinetic energy into the animal, and just pop out the other side (to open up a blood path).
Retained energy has long been a standard method of assessing the suitability of a projectile when it comes to terminal ballistics. It’s essentially a function of the weight and size (sectional density) of a bullet, with how much speed it’s still carrying. This is how much ‘energy’ is available to dump into the animal.
While this related to hydrostatic and hydraulic shock, we are not going too much into those two subjects right now. If you want some more phenomenal reading on that subject – pop over to Nathan Fosters invaluable resource – Terminal Ballistics Research – and have a read up. But, short version – hydrostatic shock is the animal’s nervous system taking a hit, causing the ‘poleax’ effect – essentially the animal just shuts down, while the hydraulic shock is fluid compressing under pressure, causing large ‘temporary’ wound channels.
However, another of the key elements of this working properly is the projectile having enough remaining velocity when it hits the target to expand fully.
Hornady state that the minimum expansion velocity for the ELD-X projectile is 1600 fps. I have heard some people suggest it’s higher, some lower – for this comparison, we are using the 1600fps recommendation as the ‘cut-off-point’ for the projectile design to work as intended – full expansion transferring all energy from the round into the animal.
As an aside – Nathan’s work has shown that 2600fps seems to be the magic figure for effective Hydrostatic shock – something none of the above have beyond 250 meters. That’s not to say it should just be a race for more velocity (the Weatherby effect) – because super fast and small projectiles can lead to rounds essentially shattering/splattering on impact – meaning low penetration and a failure to effectively transfer energy into the animal. Large projectiles (meaning bigger that .338) can help with the shock factor – but this certainly doesn’t mean I am suggesting you carry a .50 call around with you.
It does hover give some credence to the South African hunter’s preference3 for things like the H&H monster rounds. On the flip side though – too much weight in the bullet – and it simply might not stop fast enough – passing through a smaller animal before transferring all its energy. You can be both over and undersized and powered when hunting. Anyhow, I digress.
If we look at the above chart – we can basically start seeing some ‘recommended’ limits for the cartridges we are looking at. For a .308 – we no longer have enough velocity beyond 600 meters. Realistically, this is a longer shot than probably 90% of hunters should ever take anyhow. I personally include myself in that percentage.
What I find interesting to mull over though, is even though that 300WSM is showing less velocity than the 6.5PRC at distance, the WSM has significantly more retained energy. However, this could be said to be related to the amount of felt recoil between the two cartridges. Felt recoil can relate to how we shoot our guns – and more, how well we can manage recoil and see the results of our shots. Not everything goes 100% to plan every time – so seeing our impact (or miss) becomes even more important at distance. Not everyone has a spotter with them to call their shots – for solo hunters, we need to be able to stay on target once the shot has broken.
Conclusions / Summary
Don’t really have many. This really is only a small part of the considerations that come into play when it comes to cartridge selection.
Availability of firearms and ammo, components if you reload, system weight, recoil, noise – all factor into your choice. Is it a bush/tops/mountain/estate gun?
However, looking at things impartially on ‘paper’ is often enlightening. Though, raises more questions than answers sometimes.
I am also interested to look into the use of the ELD-M projectiles more – I have read several reports of guys using them to distance with a great deal of success. being the M actually has roots in the A-MAX projectile – certainly a valid hunting round – it’s quite possible that the higher BC scoring M might be a better choice than the X.
While nothing beats real-world experience in the matter – the impartial maths of external ballistics can get us a long way there. More soon!