Firing mechanism on gun initially for pistol (5)

I believe the answer is:

glock

I'm a little stuck... Click here to teach me more about this clue!

'pistol' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'firing mechanism on gun initially' is the wordplay.
'firing mechanism' becomes 'lock' (I can't justify this - if you can you should give a lot more credence to this answer).
'on' says to put letters next to each other.
'initially' says to take the initial letters.
The first letter of 'gun' is 'g'.
'lock' put after 'g' is 'GLOCK'.

'for' acts as a link.

Can you help me to learn more?

I've seen this clue in The Guardian.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.