Well, I'm still planning on housruling the entire ammunition and weapon fluff at some point because I'm a 'gun person' and I want calibers. I have no problem with your rules, and I agree that the ammo prices get ridiculous. Actually, they start ridiculous and get more ridiculous as they go.
I wanted to make a character (he'd be the rigger, so not for this campaign anyhow) who took old guns and pipes and stuff and hacked together awesome weapons like shotgun pistols, Obrezes, troll-portable 120mm cannons, and all sorts of goodies. I'm still going with a sniper for this one, probably. Or an infiltrator. I guess that depends on where we go with the campaign.