A beam will never shoot when Link is under the maximum amount of hearts (Misc 1).
EDIT: Developers, if you are creating a test quest for this bug-reproducing procedure, I recommend you go to this thread and fix the issue in there first.
Peril Beam Scroll not functional [635]
The Peril Beam will never fire if the sword in question cannot shoot beams.
But, I shall now make this check more precise. That should fix your woes.
* Now, the Peril Beam will fire for all swords, except for those whose non-percentage Beam Heart requirement exceeds the maximum possible Heart Containers (12 or 20). ( _L_, 2007-11-02 02:19:41 )
Can you give me the full meaning of this change?
I cannot confirm it fixed. Peril beam still does not work.
Here are my specifications for the Peril Beam and the Swords I am using in my custom quest (read carefully):
Scroll: Peril Beam
Level: 1
[noparse]<unused> 1[/noparse]
Maximum Hearts: 1
Equipment Item checked
Sword 1 (Wooden)
Level: 1
Damage: 1
Beam Hearts: 17
Beam Damage: 100
Equipment item checked
B.H. Is Percent unchecked
B.D. Is Percent checked
Sword 2 (White)
Level: 2
Damage: 2
(Misc and Flags are the same as Sword 1 (Wooden).)
Sword 3 (Magic)
Level: 3
Damage: 4
Beam Hearts: 100
Beam Damage: 100
Equipment Item checked
B.H. Is Percent checked
B.D. Is Percent checked
Bug still occurs in 660.
Check at shardstorm.com. Fixed twice by _L_.
* Fixed the other bug that was preventing Peril Beams from firing. Sorry!
Turn this into a 
.
Now turn it dead.
Confirmed fixed in 668.