There are swordsmen, and then there are swordsmen. A warrior who devotes his life to the study of martial combat and the characteristics of a single type of weapon can become a weapon master—a fighter whose precision, quickness, and skill are virtually unequaled anywhere.
Weapon masters are rare characters. Only single-classed fighters can ever achieve weapon mastery, and even then they do so with time, study, and sacrifice. To achieve mastery in a weapon, a character must first specialize in the use of that weapon. Then, at any time after he reaches 5th level, he can spend another proficiency slot to become a weapon master. He can continue to devote proficiency slots to the study of his chosen weapon, but can’t progress faster than the rate at which he gains new weapon proficiency slots. So, a character who becomes a master at 5th level couldn’t acquire his second slot of mastery until 6th level, his third until 9th level, and so on.
Generally, only weapons that require some skill to handle or that have a history of cultural identification are chosen by weapon masters. Swords of any kind are the most common weapons mastered, followed by bows and then axes or spears. Polearms, crossbows, and firearms are the subject of weapon mastery only in rare cases. The DM can decide that a weapon isn’t appropriate for mastery at his discretion, but he should do so before a character chooses to specialize in it.
If a fighter spends another proficiency slot on a melee weapon he already specializes in, his attack and damage bonuses increase to 3 and +3, respectively. For bows and crossbows, his point-blank bonuses increase to +3/3 as with melee weapons, and he gains an additional +1 to hit at all other range categories, for a total of +2. (Remember, this bonus doesn’t take range modifiers into account, so the archer has a total of +2 at short, +0 at medium, and –3 at long range, if the penalties are factored in.)
By spending a second slot on mastery, a character can become a high master. By this time, the character has spent four slots on a single weapon and is at least 6th level. High masters increase the speed factor of their chosen weapon by -2. High masters also score critical hits on rolls of 18 or higher.
High masters who specialize in bows, crossbows, or slings gain a new range category: extreme range. For all weapons, extreme range is 1/3 farther than long range. Extreme range shots have a –10 penalty to hit before adjustments are made for the effects of mastery.
Mastery beyond High Masters is something only of pure myth and legend.