The most common and most likely answer to this crossword clue is the 8 letter word UNLOADED
I've seen this crossword clue in The Daily Telegraph
U
N
L
O
A
D
E
D
Buddy explains!
The straight part
We know that "Lacking weight/emptied the Chamber" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lacking weight/emptied the chamber = unloaded.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNLOADED mean?
UNLOADED verb- To remove the load or cargo from (a vehicle, etc.).
- To remove (the load or cargo) from a vehicle, etc.
- To deposit one's load or cargo.
- To give vent to or express.
- To remove (something previously loaded) from memory.
- To discharge, pour, or expel.
- To get rid of or dispose of.
- To deliver forcefully.
- To ejaculate, particularly within an orifice.
- To draw the charge from.
- Not loaded.