We have experimented using SAR21 to replace the carbines but the
last time i heard it is not very successful. I am not aware of the
current status.
The MG which SM1 uses is the same as what the rest of the army
uses. Each turret have two co-axial MG. It is called co-axial
because it is specially modified to fit into SM1. Two major
diffences is that the MG do not have a butt and the gas regulator
is fixed. Removing the butt is crucial because of the close
quarters in the tank, furthermore the co-axial MG inside the turret
is mounted on and fired from a fixed bracket so there is no need
for a butt. Now for the above question,we only abandon the tank
when it is damaged beyond repair or have the risk of falling into
enemy hands. We must 1st destroy the disabled tank as much as
possible eg dropping grenades into the turret, thus there is little
time to dismount the co-axial in such situations. Most importantly
our MG cannot be fired effectively like a GPMG since it do not have
a butt and gun mount. Hope i am of help. 
