Aliens (1986) - Still holds up like crazy! FX and Sound Design Qs

Okay, just rewatched Aliens (James Cameron, duh) and holy crap does this movie still deliver. The practical effects are just...chef's kiss. I'm always blown away by the sheer scale of the sets and the creature design. Seriously, compare this to so much CGI garbage these days. I'm a sucker for miniatures, and the colony on LV-426 is incredible. Anyone know specifically what techniques they used for the atmosphere processor explosion? Looked like a mix of explosion and stop-motion, but the DETAILS! Beyond the visuals, the sound design in Aliens is what REALLY got me thinking this time. Particularly the pulse rifle sounds – so iconic! The squeal of the facehuggers, the guttural roars of the aliens... it all just works. It's such an integral part of the tension. What was the process in that era? Were they all recorded sounds or layered in? Any anecdotes I also REALLY appreciated the character development (Ripley is such a badass). I'm curious what everyone's favorite set piece is since it seems that even the best of the best get picked apart these days for not holding up. One last thing: Was it just me, or did the smartgun sound a LITTLE muffled in certain scenes? Maybe it's my setup, or maybe it was a deliberate choice to make the weapon sound more powerful? Thoughts?