This might be subject to discussion, but AP and Sentenza are both the fastest guns when it comes to mobility. Fast shots, no knockback and a large magazine, everything you need for a good hit & run weapon.
The charge on the other side nails you to one spot for the duration of 5 fast shots, the bird and reloading.
I rarely ever see anyone charge them - for good reasons. The 5 shots are not bad against stationary enemys, but against everthing else they're useless. If you could aim while the charge fires, that would be a completly different story, though. But that's not, what I want to propose here.
What would really give the charge the certain edge would be to just skip the 5 shots. The bird itself is, if wisely used, immensely powerful and infinitly more useful if on it's own.
One might argue if this was a nerf, as the charge would be stripped of the damage of 5 regular shots, but the versatility of just having the bird makes more than up for that.
However, this is of course just an idea, so whoever feels like writing elaborate feedback to this, is welcome to do so.
The birds on charge are the useful part of the charge, full-auto is for the autogun line.