To investigate the advantage of replica molding technique in more realistic conditions, special ballistic tests have been done firing small caliber type of munitions (7.65 mm Browning), in manner to produce a quasi-frontal impact of projectiles on hard steel surfaces.
As one can see in Fig. 3, using the planar replicas allows overcoming some of the most crucial bottlenecks of the compari-son performed with the direct deformed samples that usually enhance the criticalities mentioned before and concerning the illumination and handling.
To prove advantages arising from the use of planar whole replica of bullet lateral surface, higher magnification optical images obtained with a standard epi-illuminated microscope have been reported in Fig. 4.
Here two corresponding groove areas of two different bullets fired by the same pistol are laterally aligned.
Besides the standard alignment procedure further analysis of planar replicas can detect the presence of characteristic lengths-cales in these areas.
In Fig. 4C and D, the power spectrum density function (PSDF) [22] of the chosen areas are reported; a good description of the information carried by these data can be found in a detailed paper by Biscarini and coworkers [23] and in a previously published paper concenrning firing pin comparison [14].
Briefly here one can see that both the slopes, the crossover between different slopes and the peak location can be associated with good accuracy.
These parameters describe the presence of different characteristic lengths in the images.
It is worth under-lining that these kind of analysis is better applied to real three-dimensional topographic image rather than to the two dimension-al optical images, but the latter can be most commonly found in a analysis laboratory so we wanted to show that it can provide a first level of association of the whole information included in the images in terms of the presence of periodicities and specific correlation lengths.