What is different about the bullets in the new cartridges?
The shorter twist of the new cartridges allows the use of ballistically optimised bullets. The smartest way to bring more power to the target is not to lose it in flight due to an unfavourable bullet shape. As our comparison has shown, the modern bullet has only half the velocity loss compared to a classic bullet. That is the average difference between a .308 Winchester and a .30-06 Springfield at just 100 metres! A positive side effect is also a lower wind drift, also only half that of a classic bullet. The higher rotational speed also improves target ballistics, as the more spin-stable bullet responds more quickly to the target. Even a 2″/5.08 cm shorter twist increases the effect on the target by approx. 10%. Mind you, all this without more powder, gas pressure and recoil.
Cartridge profile with technical specs: the 7mm PRC (Precision Rifle Cartridge) from Hornady
It was primarily the development of Hornady’s ELD bullets with precise analysis using Doppler radar that led to today’s findings. Conversely, one could also say that the new cartridges are necessary in order to be able to use the modern, high-performance bullets at all.
1. An adapted, shorter case so that the new, longer bullets fit into the standard overall cartridge length and thus into existing rifle actions. The case volume is optimised for an optimum charge density with modern propellant powders. Hornady has even worked together with the leading powder manufacturers to develop the optimum propellants.
2. A more efficient case geometry with a wider and shorter powder column, a minimised case taper (almost cylindrical) and a steeper shoulder angle. This improved case design not only enables more effective powder conversion, but the steep shoulder also ensures a very precisely defined headspace. A shoulder angle of 30 degrees has proven to be the optimum compromise between ease of loading, powder conversion and barrel life. Classic carrtridges usually have a flat shoulder angle of around 20 degrees. The resulting optimised charge density also ensures lower velocity fluctuations. The brand new 7mm PRC is about 4% more effective than the 7mm Remington Magnum thanks to the case design alone. That doesn’t sound like much, but 4% is the average difference in performance between the .308 Winchester and the .30-06. These findings go back to the development of the .17 HMR rimfire cartridge in 2003.
3. Lower tolerances of the chamber and barrel throat to the cartridge ensure significantly improved precision and insensitivity to the unavoidable bullet jump (the distance a bullet travels before it touches the rifling) in factory cartridges. While classic cartridges have a freebore (transition from the chamber to the rifled barrel section) that is 0.05 to 0.18 mm larger than the bullet diameter, this dimension is only 0.013 to 0.015 mm in modern cartridges – and demonstrably without any loss of practicality in terms of fouling and accuracy.
4 Thanks to this good efficiency, modern cartridges achieve the increase in performance without a significant increase in gas pressure (usually only 180 to 500 bar). In most cases, the maximum pressure is approx. 65,000 psi/4,482 bar, which both rifle actions and case material have been proven to withstand reliably over the long term.
With a barrel length of 61 to 56 cm you have practically the full performance yield, but with this efficiency and performance the 7mm PRC, like the other new cartridges mentioned, is also ideal for the short barrels down to 50 and 46 cm that are so popular in hunting.
