When black powder was used as a propellant, the extremely heavy fouling produced was a major problem. After a few rounds, the bore became so heavily fouled that subsequent rounds would hardly touch the rifling, leading to a subsequent fall-off in the weapon's accuracy.
In an attempt to counter this problem, a whole variety of rifling profiles were designed with each claiming to have distinct advantages over the rest. Every shape imaginable was tried at one time including square, round, triangular, ratchet, comma and polygroove rifling, which looked like the petals on a flower (Figures 4.9-4.16). Whitworth and Lancaster, both very prolific arms inventors, were both very successful with oval (Whitworth), bored and square bored (Lancaster) rifling.
With the advent of smokeless propellants, the necessity for these complicated rifling profiles and their expensive production costs virtually disappeared.
Figure 4.9 Polygroove rifling.
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