Oath of Death (1971)
Three rebels join forces and swear a blood oath, but one of them secretly has grander ambitions and when he gains an official rank with the occupying Tartars he forsakes his oath.
Chang Cheh and I Kuang have balls claiming writers' credit for The Blood Brothers, as whilst the details differ it's basically the same story as OATH OF DEATH from two years earlier, which was written by Chin Shu-Mei (Pao Hsueh-Li's wife!).
Chang Cheh may have had bigger stars and budget but Pao Hsueh-Li goes hard on the action, with dynamic camera work and buckets of blood - culminating in a classic ultraviolent Shaw Brothers finale.
Despite opening and closing with action there is a long down time in the middle where there is very little, though the plot is interesting enough to keep things ticking until the violence erupts again.
There's also some mild nudity, which was not actually common in Shaw Brothers films at this point in time (it would change over the next few years).
BLOOD BROTHERS is still the better film, developing its themes more effectively and with higher production values. As its scrappier, more ferocious predecessor, OATH OF DEATH deserves to be better known than it is though.