You've pretty much got it, seemingly from first principles, good job!

Yeah, thats... basically exactly what happens.

Now, fully cleaning the gun after every usage... well, on the one hand, theoretically that would help with the gun being ... less of a profilic random micro/particulate lead dispenser.

On the other hand, well, all that lead is now literally being handled by you, so, you need gloves, maybe a mask, maybe functionally a clean room as well.

At that point, you might as well be a small armory, if you want to have all the stuff and practices in place to properly contain the particulate lead.

Another big element at play is that different barrels basically corrode or gunk up differently.

For example, chrome-lined barrels are generally slightly more expensive, have essentially greater durability or longetivity, but because of imperfections of the actual lining process, lead to slightly less accurate barrels.

Chrome lined barrels would presumably have less lead exposure factor, due to lead having a harder time to stick to the barrel.

Vs non chrome lined barrels that gunk up more quickly, but, when clean, can be slightly more accurate.

There are other ways of coating or treating or just making a barrel, as well as many other kinds of seemingly esoteric details of gun design, that could potentially affect how much of an... 'ambient particulate lead exposure' risk it is.

I totally agree with your Ziploc bag analogy lol. If the only concern was reducing lead exposure, I bet just a plastic bag would be enough. However, if we are only talking about using the weapon and bringing it home, does storage really matter? If the particles are all over your clothes, you are just dragging that lead everywhere.

I'm thinking it's more to do with what one of the other commenters said, lack of storage suggests a certain attitude. If you're not storing it, you are probably moving it around the house, cleaning it on the table, etc. So maybe both groups of people have the same amount of lead on their weapon, but the storage group takes it straight to the gun safe instead of leaving it in their pants and letting it sprinkle heavy metal surprises around the house?

Yeah I think this is part of it. I think it has less to do with the storage and more to do with the other activities. Maybe someone who doesn't lock up their gun is more likely to clean it on the kitchen table, for example

Yep, basically this.

Bullets have lead in them.

Lead is actually fairly fragile, malleable, degradeable, and also of course, a neurotoxin, in high enough concentrations.

People that handle guns and/or ammo extremely regularly?

In many cases they use gloves, in some cases even masks.

Kinda like how xray techs get the (ironically, lead) shielding, but you don't: its the dosage, the exposure.

Most legit gun ranges in most states have a whole set of regulations and systems/practices in place to handle all that lead.

I'm not sure exactly how indoor ranges do it, but most outdoor ranges in most states, the backstop birm that catches all the bullets?

Gotta adhere to different kinds of water drainage requirements, do something like dig the whole thing up and process it in some way, to literally get the lead out, every so many years.

Even when guns aren't being fired, you've got similar sorts of safe handling practices for armorers/armories, people that recase (wrong term?) spent brass to make their own rounds, people that are very often doing basically surgery on guns, etc.