WHAT THE WRITING ON YOUR AMMUNITION BOX REALLY MEANS

Ballistics expert Paul Bradley explains how to interpret the information on ammunition boxes – helping retailers guide customers more confidently and avoid common misunderstandings at the counter.

Many of us will have stood in our local gun shop browsing ammunition for our next hunting or target shooting trip. While you may have a personal preference there is no guarantee that they will have it in stock. Or maybe you are still searching for a product you can really have confidence in. One of the only ways we can assess ammunition in the shop is to read what is written on the box. However, this information can be misleading if we do not understand its context.

The first thing shooters likely look for is information regards the caliber. Thankfully when buying full built ammunition this should not be a problem for most people although there can be a few pitfalls. In Europe and the UK, the dimensions of chambers and ammunition are regulated by CIP. In the most part this ensures things run very smoothly. You can buy ammunition designated to your guns caliber and it should at least work safely. There are a few odd caveats though. Some magazines may not accommodate a round built to CIP max overall length. In the case of the 338 Lapua Magnum you may even find that the round will not chamber if built to full length with specific projectiles (250gn SMK being one such example). With that in mind it might be nice to see the actual overall length on the box.

The next thing shooters will look for is a bullet description which will help them to know what sort of characteristics a round may have. Is it expanding? Is it a lead core? Does it have an opening at the tip or the base? There are a lot of mistakes that can be made here because there is no standardised projectile description, many companies have their own acronym or name. Even the most common bullet acronyms can cause confusion – The hollow point boat tail is hollow point in design but not in nature. There are plenty of new hunters who will have purchased HPBT thinking they have an expanding hunting round when in reality it has little if any expansion possibility. The “hollow point” is merely an effect of the manufacturing process, the jacket being swaged around the lead core from back to front leaving a very small opening at the tip. To make things even more confusing a BTHP may also be called OTM (open tip match). The acronym was bought about in hope that it would remove the association with hollow point rounds but has in fact just added another layer of confusion! Of course, we then have hundreds, if not thousands of names and acronyms on the market which have been invented by a brand marketing department. So many in fact that it would be impossible for me to write a descriptive list without much more spare time and the whole magazine to fill. The best bet here is to discuss with users and shop staff the features of each product before you take the leap and purchase.

The next thing you might check on the box is suggested twist rate. Many people believe that the weight of the projectile is the vital variable here, but it is the length. Longer projectiles need a tighter twist rate to stabilize them. Of course, a few years ago, pretty much every projectile on the market was a lead core copper jacket variant so weight was a great indicative factor for stability/twist rate. Now we have many different materials being used – pure copper, brass and even some tin. These are all lighter than lead core counterparts and will be longer so care must be taken.

Shooters will often discuss the BC (ballistic co-efficient) of their chosen product. The BC details the drag efficiency of a projectile when compared to a standardised form factor. The first confusion is between the two form factors referenced. G1 refers to a more traditional bullet shape, a flat base without the taper of a boat tail. If you are buying a round using a bullet of this form factor then G1 is definitely the way to go to achieve reliable ballistic data and assess the performance. G7 refers to the modern bullet shape, a hollow point boat tail projectile being a simple example. G1 numbers tend to be larger than G7 and they have been around a lot longer. For this reason many ammunition manufacturers only state G1 even if it compares to a different form factor. Partly because customers are used to G1 and partly because “bigger numbers look better”! We should also note that these G numbers will change based on velocity and even specific rifles or muzzle devices. A muzzle device that creates a bit of yaw for example will reduce BC. Manufacturers will always give you best case scenario. Bryan Litz does a great job of listing G1 and G7 BCs for popular bullets both in his books and ballistic apps. He used an average taken by Doppler radar from a wider velocity band, rather than best case scenario.

The last point I will discuss is, in my opinion, the least useful piece of information on the box but is often the first thing that shooters will look for – Velocity. It is great to have high velocity, it gives a flatter trajectory and is less sensitive to wind effect. I have often heard customers complain that the velocity on the box is “wrong” or is false advertising. We cannot entirely rule that out, but the most likely explanation is all about context. The manufacturers stated velocity is usually taken from a proof barrel. This may be several inches longer than your 24-inch hunting rig. What was the air density when the shots were taken? What was the condition of the bore? A bore with many rounds through it will give vastly different velocities to a brand new one if it has been produced to a high standard. One should never use the velocity on an ammunition box as a basis for ballistic data. A velocity reading is a system output not purely ammunition based.

Hopefully we have learned that the box information serves as a guide only. The best solution is to buy a box and test the rounds yourself for velocity. For the factors you cannot test such as terminal effect, then the internet, fellow shooters and the folks who work in the shop are all useful sources of information.

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