If a real Apocalypses happened these ideas I think would allow for indefinite Survival with firearms and is what I'd do in the player character's position.
If I knew how to make something like this I so would do it my self, but I don't even one were to start so here's the ideas out to anyone that can make it happen.
Three new types of ammo for the blunderbuss
1. hard hitting steel cannonballs, made of 5 gunpowder, one paper, and one steel ball that can be made in the forge.
make the blunderbuss decay 500% more every shot but behaves like the new breaching shells, doing a lot of damage to blocks and the gun.
Requires the same perks as the breaching shells to not be op
2. Stone cannonballs that take 3 stone, 1 gunpowder and 1 paper, basically a lite loaded slug for more range and accuracy at the cost of less damage.
Turn your blunderbuss to a big musket, no perks needed just twice the time to craft
3. Lead cannonballs made from 1 lead ball, 3 gunpowder, and 1 paper. same as above but does more entity damage and needs the perk for slugs.
Does 250% more damage to your blunderbuss every shot.
That's the main part I want but anyone thinks the stuff below is possible than even better, honestly if any of this is made I'll be real happy.
1. Reinforced Blunderbuss: basically my idea is a more durable, more expensive one that has a better stock that would be better suited to aiming and doesn't look like you made it out of driftwood in 10 minutes.
Stat wise more durability and slightly more range and accuracy and looks like something you wouldn't put to your face to look down the sights and think to yourself "what the heck am I doing"
2. Musket: would be a alternative to the hunting rifle with a little less damage, range and accuracy, longer reload and cheap ammo.
Would be made from forged iron and wood and need the recipe for the hunting rifle to craft and can't be found, but doesn't need weapon parts.
The Musket ammo would be made from 3 gunpowder and 1 bullet tip
I'm mainly posting this hear as sadly I doubt The Fun Pimps would add any of this to vanilla, but a man can dream.