actually, its never a good idea to hang grenades on your SBO. In
a real shooting war, those that "john wayne" their grenades are
more at risk of getting killed when the enemy shoot at the
grenades, trying to inflict more casualties among your section
mates, or the grenade pins can be pulled off by branches when
bashing or doing movement. That would mean that you have to tape
your grenades. And even that would mean that it would be difficult
to remove the tape when needed. The best tape to use is masking
tape...easier to remove than black electrical (plastic-type) of
tape.
Even in peacetime, grenades on your SBO harness are gonna cause big
bruises on your chest when you prone; especially when you are
contacted.
Just my 0.02 cents... 
