Something that fell flat about the banner scenes in Space Marine 2 was that, if you watch the individual marines, they have a firing rate of about one round every 2 seconds even though they're being bumrushed by enemeies at point-blank range. Would've hit a lot harder if they were actually unloading on their foes instead of drip-feeding them rounds like a broken faucet.
I like to think everyone there is so low on ammo at that point that they are conserving rounds, using a Stand or Die tactic and coordinating fire on the closest/priority targets with persicion instead of wasting ammo in that moment. Ultramarine are extremely tactical and know tactics like breathing air. Wasting ammo in this stand would make it so reinforcements would have less of a chance to reach them.
Ammo is not cheap. Even Space Marines are trained not to waste shots. Typically, they only use enough ammo as needed unless they are Dreadnoughts. But, tbf, who the hell is going to tell a Dreadnought not to spray and pray?
