48 seconds was my record - my BMT section commander had too much
of an ego to be pleased about it. 
Anyway, lesson learned from hard experience is that you ALWAYS
release the bolt before slamming the new magazine in. The magazines
are so soft that if it slap them in too hard, they go in too far
and jam the weapon - this applies especially to the old, beat-up
magazines used for training.
The forward assist was introduced when the propellant for the 5.56
round was changed. The new propellant left more carbon in the
chamber, and the bolts sometimes did not go all the way forward
when the charging handle was released. In such situations, the
forward assist was used to push the bolt forward.
I'm from too long ago to know about the SAR-21, and I'm too
decrepit to remember the exact procedure for loading the SAW. If I
recall correctly, it was:
- remove old mag
- put in new mag
- pull charging handle
- stare incredulously at the handle that came off in your
hand
- curse and swear as you try to slide the damned thing back into
its rail
- run along to catch up with your section mates, who by that time
have gotten 100 metres ahead of you. 
