Handloading the FN 5.7x28mm
Date: Jan 01 2010
Development of the FN 5.7x28mm began more than 20 years ago and was first introduced in a submachine gun for military applications in the early 1990s. A tactical handgun followed in the late 1990s, and by 2005 a civilian version appeared. The cartridge is advertised to push a 27-grain lead-free bullet at 1,950 fps, a 28-grain lead core bullet at 2,050 fps (now discontinued but will return in 2010 due to demand) and a 40-grain lead-core Hornady V-MAX bullet at 1,700 fps.
The current civilian tactical handgun, known as the Model Five- Seven USG, is an autoloader with a 20-round capacity. It is constructed of polymer with appropriate parts being alloy and steel. Sights are fully adjustable. Barrel length is 47/8 inches, and weight is around 24 ounces empty.
The 5.7x28mm cartridge is a bottleneck design that utilizes .22-caliber (.224-inch) bullets. The shoulder angle is 35 degrees. Water capacity (measured to the bottom of the neck) is 11.1 grains. It is a proprietary cartridge, so there are no pressure guidelines or industry standards for handloading. Clearly FNH USA (www.fnhusa.com) would rather sell ammunition than encourage handloading that would produce ammunition for a fraction of the price.
In discussing the cartridge with a company representative, it seems that factory fodder is loaded at something close to 50,000 psi, a figure that has been confirmed by at least one lab that I am aware of. At the time of this writing, only one factory load, the 40-grain version, was available for evaluation. This load was closely scrutinized to learn as much as possible about pressure curves, velocities, function, priming,
case strength, etc., so that handload data would be safe and reliable.
Handloading the 5.7x28mm posed a number of challenges and oddities that have never been observed in any other cartridge. For instance, upon retrieving fired cases (from factory loads), it was observed that the case body had a slight reversed taper, as it measured around .007 inch larger in diameter at the shoulder than at the case head, which is simply mind-boggling! Factory loaded ammunition has essentially no taper from the case head to the shoulder or is not more than .001 inch smaller at the shoulder than at the head (a figure that is supported by C.I.P. drawings). Cases were also obtained that had been fired from two other FN Five- Seven USG pistols, and they had a similar reverse taper. Clearly FN is cutting the chambers to this odd dimension, and there is no explanation as to why. Due to the above dimension issues combined with a bottleneck case that should be full-length resized to achieve proper chambering, case life is not long and signs of case head separation began to appear after just a few reloadings.
Adjusting the sizer die is different than that of conventional cartridges. The sizing die body should first be set in conventional methods. To prevent cases from being crushed while sizing, due to the expander ball and sizer die trying to accomplish their respective jobs at the same time on so short a case, the expander assembly must be adjusted so that it extends as far down as possible. To accomplish this, place a case in the shellholder and raise the ram to its highest point, then screw the decapping assembly down until it bottoms out on the inside (or head) of the case, then turn it up one-half turn and set the locknut.
Powder selection is critical for the 5.7x28mm. Disassembling factory loads (as assembled by Fiocchi USA) revealed that they contained 5.1 grains of ball powder, which was not even close to filling the case. There were several powders that proved capable of duplicating factory load performance such as Accurate AA-5, AA-7, Ramshot True Blue, Vihtavuori N105, Hodgdon Universal and Alliant Power Pistol. Although performance was certainly acceptable, just like the factory powder, the above propellants failed to fill the case.