Skyrim:Gauldur Blackbow

Leveled Item: Gauldur Blackbow (000f5d22); (All statistics are for level 36+ version);
Type	Bow
Editor ID	dunGeirmundSigdisBow06
Statistics
Damage	14
Speed	0.875
Tempering	Steel Ingot
Enchantment
	Absorb 30 points of magicka: Drain Magicka, 30 pts for 1 sec;
	Absorb 30 points of magicka: Drain Magicka, 30 pts for 1 sec;
Charge/Cost = Uses	3000/70=42

The Gauldur Blackbow

The Gauldur Blackbow is a special ancient Nord bow found at Geirmund's Hall in the possession of Sigdis Gauldurson. The weapon's enchantment drains magicka from whoever is hit by one of its arrows for one second. Tempering the Gauldur Blackbow requires one steel ingot and the Arcane Blacksmith perk. As is customary for honed draugr weapons, the benefits of tempering are doubled if you have acquired the Dwarven Smithing perk.

Related QuestsEdit

Level				Charge/Cost = Uses	Enchantment	Object ID	Editor ID
1-11	12	253	8	500/21=23	Absorb 10 points of magicka: Drain Magicka, 10 pts for 1 sec	000a5def	dunGeirmundSigdisBow02
12-18	12	407	8	1000/32=31	Absorb 15 points of magicka: Drain Magicka, 15 pts for 1 sec	000f5d1f	dunGeirmundSigdisBow03
19-26	18	530	14	1000/45=22	Absorb 20 points of magicka: Drain Magicka, 20 pts for 1 sec	000f5d20	dunGeirmundSigdisBow04
27-35	18	750	14	2000/57=35	Absorb 25 points of magicka: Drain Magicka, 25 pts for 1 sec	000f5d21	dunGeirmundSigdisBow05
36+	18	972	14	3000/70=42	Absorb 30 points of magicka: Drain Magicka, 30 pts for 1 sec	000f5d22	dunGeirmundSigdisBow06

It appears from testing that the level of the Blackbow is set either when you read the book to gain the quest or when you get near enough to the dungeon that the entrance "spawns". This doesn't mean actually finding the entrance, just getting close enough that the game loads the dungeon entrance cell. If you want a high level item not only do you have to avoid reading the book but also avoid the geographic areas of the dungeons themselves.