Random generation Metalline weapons...

[KylarJ]

...shouldn't also be "silver" or "adamantine" etc.

Might want to check the formulae used there

e.g. "+4 metalline byeshk kama of maiming"

(Especially if the (redundant) byeshk quality puts up its min level).

[Sirea]

It's probably just leftover code from when Metalline was Transmuting and also covered things like Slash/Pierce/Blunt and allignments.

Sloppy coding? Yes. Redundant? Yes. Likely to be fixed soon? No.

[Junts]

This happens because metal effects are not considered an enchantment prefix; they're totally free modifiers that simply improve the base price of the item. While this is mostly useless, it does have two effects, one of which is more helpful than the other:

Metalline does not simulate the dr/good bypass property of flametouched iron. Therefore, a metalline flametouched iron weapon breaks both metal and good drs. A plain metalline weapon will not do this. A metalline FTI of greater evil outsider bane weapon would be extremely powerful, as you might imagine

Second, metalline is an enchantment effect. Mordenkainen's disjunction removes it. While there's not presently any mob that both requires a metallic dr bypass and has mordenkainen's, its not out of the question. Mord's temporary disenchant has no bearing on the actual metal of the item, so it'd serve as a helpful backup in such a situation.

[mgoldb2]

(Especially if the (redundant) byeshk quality puts up its min level).

One additional benefit that Junts did not mention is that byeshk for example will increase the hardness of the weapon which metalline does not.