So, I decided to post it for those who cannot complete the achievement in hl2ep1 “Lone Bullet”, where you need to shoot only once during the whole game. Here you and Alix are already riding the train, and this achievement is immediately unlocked.
Half-Life 2: Episode One: Save Game [Achievement “Lone Bullet”] Free Download
Throw files into the folder “… Steam \ steamapps \ yourlogin \ half-life 2 episode one \ episodic \ SAVE”