So the military has decided to take me away from Florida and put me into Cali. I have no clue what the gun laws actually are and what I can or cannot have.

No regular ar-15s? What about gen 5 glocks or things like glock 43s? I’ve got hundreds of 30 round mags and tens of thousands of rounds in total…can I bring them or am I going to be out straight into jail?

Can I just transport everything and put it in a closet then take it out years later when I leave?

No regular AR15s.

No magazines over 10 rounds.

You can import your non-assault weapon (anything that looks like an AR-15) firearms and ammo. Firearms need to be registered via the new resident report of firearm ownership (see here: https://oag.ca.gov/firearms/ab991)

See this roster? This is what you can legally purchase new while you are here. If you want anything not on this list, then buy it now and import it with you.

Hope this helps... welcome??

There's a sticky above. Probably current but haven't looked recently.  The Ca DoJ/Attorney General's website has the current definitions of firearms that can't be imported.  Basically, you can't import "assault weapons" and there are some others.  There may be an exception of some sort for active duty but I guess it's not simple and may depend on command support?  For typical pistols (not mags outside the pistol grip, etc.) the threaded barrel (it's a no) is the issue.  The Handgun roster applies to new  in state handgun sales.  You can import a handgun not on the roster as long as it's not an "assault weapon."  People have been known to sell off roster handguns after arrival.  It's legal, assuming the FFL/transfer rules are followed.

The "rifle" rules basically fall into two categories of non-assault weapons, "featureless " - has none of a list of features.  Or a semiautomatic, centerfire rifle that has a fixed magazine with the capacity to accept 10 or fewer rounds.  These can have any or all of the "features" on the list. Noting “fixed magazine” means an ammunition feeding device contained in, or permanently attached to, a firearm in such a manner that the device cannot be removed without disassembly of the firearm action. So these are the ones generally using a device which separates the upper and lower sufficiently to then not fire and allow for replacing the feeding device.  (The prior iteration was the bullet button, so the feeding device need a "tool" to release., now "disassembly.")  so one can follow either modification path and some types of firearms are more amenable to one of the other.

No feeding devices over 10 rounds can be imported legally.  I don't know if there are ammo quantity limits.

No magazines over ten rounds for EITHER handguns or rifles - none!

There are several devices available to make your rifle(s) California-compliant - butt stocks, magazine locks, action locks, muzzle devices,...  The bans created a huge "cottage industry" of innovation.

A simple thing to do, if you are in doubt, separate the upper from the lower.  No matter the features, neither half is an assault weapon.

I'll post this here for your convenience -

Link to DOJ web site

   A semiautomatic centerfire firearm that is not a rifle, pistol, or shotgun, that does not have a fixed magazine, but that has any one of the following:
       A pistol grip that protrudes conspicuously beneath the action of the weapon.
       A thumbhole stock.
       A folding or telescoping stock.
       A grenade launcher or flare launcher.
       A flash suppressor.
       A forward pistol grip.
       A threaded barrel, capable of accepting a flash suppressor, forward handgrip, or silencer.
       A second handgrip.
       A shroud that is attached to, or partially or completely encircles, the barrel that allows the bearer to fire the weapon without burning the bearer’s hand, except a slide that encloses the barrel.
       The capacity to accept a detachable magazine at some location outside of the pistol grip.
   A semiautomatic centerfire firearm that is not a rifle, pistol, or shotgun, that has a fixed magazine with the capacity to accept more than 10 rounds.
   A semiautomatic centerfire firearm that is not a rifle, pistol, or shotgun, that has an overall length of less than 30 inches.

For purposes of this section, “fixed magazine” means an ammunition feeding device contained in, or permanently attached to, a firearm in such a manner that the device cannot be removed without disassembly of the firearm action.

Thanks for the info guys.

Ill prob just separate everything and let it sit for my entire sentence.

So no 30 round mags at all....but what if they are taken apart? Like spring, follower, base plate and mag body all separated? I would love to not have to store hundreds of mags somewhere else for a few years.

The legislature fixed that "loophole" several years ago.  It used to be possible to legally get by mail-order a "magazine rebuild kit" consisting of all four parts in the same package.  Now that's considered constructive intent to assemble an illegal magazine.

OTOH the standard-capacity magazine ban is kind of in legal limbo.  I wouldn't advise bringing anything that holds over 10 rounds into the state.  Keep your normal mags out of California for now, and have no worries.

Thank you! Looks like I will have to bring them up to the parents and buy some 10 rounders.

There is also a list of banned "assault weapons" which cannot be brought into the State, even if they have the above-listed features removed.  The lower receiver markings should be checked for compliance.

Not exactly. The legislature banned kits that convert a 10-round or less mag into an 11+ round mag, so-called conversion kits. While mag extensions that do this exist for some mags, it largely isn't a thing. By the strict letter of the law rebuild kits are just parts if not assembled into an actual magazine.

DOJ has chosen to interpret the law to ban that and create a half ass version of constructive possession, but it's not actually in the law.