[SG] Is this legal?

I'm just wondering is this legal:

I have a squad of 8 with automatic rifles/w grenade launchers,
this gives them a 3 firepower each.

Using my first action I have 4 troopers fire at my target for
an fp die of 12.  I then use my second action to have my remaining
4 troopers fire at the same target with an fp die of 12.

It feels a little "slimey", however, I'm not terribly thrilled with
the idea that having twice the firepower have no affect on the combat.

I think I may institute a house rule that once you have your fp
die of 12 excess troops start accumulating a new die if they have
a minimum combined firepower of at least 4.

So the above case could be resolved as <quality><d12><d12>, or,
if in the second range bracket <quality><d12><d8>.

I don't know, that mechanic might work, or maybe for every excess
4 fp you have the opponents cover mods are reduced by 1.

Would this break the system?

Roger