Just the RPG? Oh wait, it still isn’t possible unless you use ammo cheat.
I think it’s a bit too small for such a vital prop.
(I am bad with achievement names): Have 1 HP left when completing the game.
Half Hour: Complete the game in under 40 minutes.
No time to loose?
Ain’t got time to bleed?
Death can’t take a legend?
I’m inmortal?
10 HP to make it a bit more realistic.
The fastest speedrun i’ve seen is 36 minutes. https://www.youtube.com/watch?v=YTUOn2EUFhk
almost no-one would get that.
Edit: I would convert the text into the link, but i’m too dense
[COLOR=‘Orange’]Hey! It’s like counter strike!
Get all the weapons
[COLOR=‘Orange’]Who Ya Gonna Call?
[COLOR=‘White’]Get the Gluon Gun
Where did hear that before? Ghost… uhm how was it? Ghostbuster. Wasn’t it?
Anyways.
[COLOR=‘DarkOrange’]I don’t like H.E.V.s
Kill Nihilanth with 0 H.E.V. Suit energy.
I almost never end up with suit energy when i kill Nihilanth. Maybe that’s just because i’m rubbish
I can’t turn left: Never turn left; over 9000 points
[COLOR=‘Orange’]Pyrotechnics: light 20 enemies on fire.
Plastic pink flamingos double as beer bongs (cut off the beak/head). Was there any beer in half life?
I’ve seen that already. In the commentary the people used methods that might not work in the source engine. 
Edit: Unknown bodypart - Kill 3 alien enemies with crouch shots!
Not a Black Mesa achievement but meh
Yeah Barney owes you a beer.
[COLOR=‘DarkOrange’]I Haz Teh Power
Get the crowbar
[COLOR=‘DarkOrange’]Cut Communications
Destroy all the military radios
[COLOR=‘DarkOrange’]Imma Chargin Mah Lazor
Overcharge Tau cannon
[COLOR=‘DarkOrange’]Shoop Da Woop/ Imma Firin Mah Lazor
Fire the Tau cannon
[COLOR=‘DarkOrange’]I Win
Kill the gornach with the crowbar only
[COLOR=‘DarkOrange’]Let’s Bee Serious
Get the Hornet gun
[COLOR=‘DarkOrange’]Self Defence
Kill a marine
Seriously? that would probably be tougher than killing the Nihilanth with a crowbar.
I just overused the rpg with impulse 101 everytime I fought against gonarch.