Are there any Federal laws (or state laws) regarding the maximum amount of smokeless powder one can have in a residence?

I do know my homeowner's insurance says 15lbs.  My insurance agent(a reloader himself) suggested an explosion-proof cabinet or store it elsewhere.  I have a climate controlled 8x16 home-built workshop, so I store the extra out there.

I also have a warning sign on my door in case the fire dept has to come out.  Most FD will not go near a room if they hear ammo cooking off.  Powder in small quantities(1lb containers or in hoppers) will simply flash off once the container melts.  You get enough in a confined location, and it can make a pretty good boom.

Now primers are a whole different ball game.  I will not have more than I need available on my bench at one time.  The rest are stored out in the shop in a sealed ammo can

Some places do have limits.  The town close to us has a 50 lb limit within the city limits.  I know some avid reloaders that have much more then that on hand!

This sounds like you've made a bomb - primers detonate.

You're trying to protect them from humidity and temperature changes and other environmental factors, right?

I would suggest you take them out of the ammo can.  Put them in something that cannot contain any pressure (Tupperware) and will not fragment into schrapnel.  Also, disperse the storage locations to prevent a large concentration.

I could be completely wrong.

NFPA rules regarding powder and primers are (generally) 50 lb. of powder and 10,000 primers.

Use your better judgement and keep everything stored in its original packaging.

There was a push to bump the primer limit up years ago and NFPA supposedly gave it the green light but the book never changed. Both limits are asinine.

In addition to any weight limits, powder should be kept

in a wooden container about 2" thick with a weak side.

Thickness might be 1 1/2", can't remember.

SAAMI

Not that I am aware of.

But, that doesn't mean there are not county and municipal laws that govern the storage of powder, primers and other hazardous chemicals in a residence.  You should check with all local governments that might be involved.  Many localities simply incorporate the NFPA code into their ordinances, so it would be a good idea to read a copy at the NFPA website: nfpa.org  You have to register, but registration is free.  The current (2018) standard is 495 and you want chapter 14.

In addition, you should check and see if your homeowner's insurance says anything about it.  And if they do, you would be well served to take pictures of your storage at home to show it was under the limit and the container was in compliance as well as keep records of your purchases of powder and your use.  If your house burns down and the insurance company can avoid paying for it because they can show you purchasing two 8 pound containers of powder that were delivered to your house when the limit per your policy was 15 pounds.

I plan on building the SAAMI box this spring, or getting a 2 compartment explosion-proof cabinet($$$, but waiting to find out what they are going to do with one at work).  I have them in the can for now, however the lid isn't latched down.  If they were to go off, it would simply blow the lid open.

Read through the SAMMI link... this caught my eye.

Lots of good info, and stuff I've never considered... I'm not a reloader, but have been thinking about it...  Anything else that I should be thinking about, or considering as I am contemplating learning how to reload?

Guess Bass Pro and other big box stores ain't read that...

And glad they didn't. How else would I snag the H4350 8lb jugs

You have to remember that most states and political sub divisions adopt NFPA guidelines as their ordinance.
In MN you can not reload (have powder or primers but no mention of ammo restrictions in a multi unit dwelling).

Primers in MN
500.3600 SMALL ARMS AMMUNITION PRIMERS.
Subpart 1. Restricted scope. This section does not apply to the transportation of small arms ammunition primers governed by Code of Federal Regulations, title 49, parts 100 to 199 (1983).
Subp. 2. Transportation and storage. Small arms ammunition primers must not be transported or stored except in the original shipping container approved by the Department of Transportation in Code of Federal Regulations, title 49, parts 100 to 199 (1983).
Subp. 3. Truck or rail transportation. Truck or rail transportation of small arms ammunition primers must comply with the Department of Transportation regulations in Code of Federal Regulations, title 49, parts 100 to 199 (1983).
§Subp. 4. Quantity limitations. Not more than 25,000 small arms ammunition primers may be transported in a passenger vehicle.
Not more than 10,000 small arms ammunition primers may be stored in residences.

Not more than 10,000 small arms ammunition primers may be displayed in commercial establishments.

Smokeless Powder in MN
7500.3500 SMOKELESS PROPELLANTS.
Subpart 1. Restricted scope. This part does not apply to the transportation of smokeless propellants governed by Code of Federal Regulations, title 49, parts 100 to 199 (1983).
Subp. 1a. Approved container required. Smokeless propellants must be stored in shipping containers approved by the Department of Transportation in Code of Federal Regulations, title 49, parts 100 to 199 (1983).
Subp. 1b. Transportation of certain quantities. Quantities of smokeless propellants of 25 pounds or less in shipping containers approved by the Department of Transportation in Code of Federal Regulations, title 49, parts 100 to 199 (1983), may be transported in a passenger vehicle.
Quantities in excess of 25 pounds but not exceeding 50 pounds that are transported in a passenger vehicle must be in a portable magazine having wooden walls of at least one-inch nominal thickness.

Transportation of quantities in excess of 50 pounds is prohibited in vehicles transporting passengers.

Transportation of quantities in excess of 50 pounds in other than passenger vehicles must comply with Department of Transportation regulations in Code of Federal Regulations, title 49, parts 100 to 199 (1983). In addition, warning placards must be prominently displayed when more than 250 pounds are being transported.

Subp. 2. Storage of propellants intended for personal use. Smokeless propellants intended for personal use in quantities not to exceed 20 pounds may be stored in residences. Quantities in excess of 20 but not exceeding 50 pounds must be stored in a wooden box or cabinet having walls of at least one-inch nominal thickness.
Subp. 3. Commercial displays and stocks. Not more than 20 pounds of smokeless propellants, in containers of one-pound maximum capacity, may be displayed in commercial establishments. Commercial stocks of smokeless propellants greater than 20 pounds but not more than 100 pounds must be stored in approved wooden boxes having walls of at least one-inch nominal thickness. Not more than 50 pounds are permitted in any one box.
Commercial stocks in quantities not to exceed 750 pounds must be stored in storage cabinets having wooden walls of at least one-inch nominal thickness. Not more than 400 pounds are permitted in any one cabinet.

§Subp. 4. Quantities over 750 pounds. Quantities in excess of 750 pounds must be stored in magazines constructed and located as specified in part 7500.0800.

Subp. 5. Separate storage. Small arms ammunition primers must be separated from flammable liquids, flammable solids as classified by the Department of Transportation in Code of Federal Regulations, title 49, parts 100 to 199 (1983), and oxidizing materials by a fire-resistive wall of one-hour rating or by a distance of 25 feet.
Subp. 6. Storage of large quantities. Quantities of small arms ammunition primers in excess of 1,000,000 must be stored in magazines in accordance with part 7500.0800.
Statutory Authority: MS s 299F.71 to 299F.83
History: 11 SR 6
Published Electronically: July 26, 2007

It appears that primer storage in residences is OK up to 150,000 per the current NFPA publication. Page 44 states:

14.5.5 No more than 10,000 small arms primers shall be permitted to be stored in residences.

14.5.6 For small arms primers classified by the U.S. DOT as 1.4S, the limit stored in residences shall be permitted to be increased to 150,000.

What does "classified by the U.S. DOT as 1.4S" mean? Well -

The safety data sheet for Federal primers
https://1pdf.net/rifle-pistol-primers-federal-federal-premium_5867d8dce12e891a022714f7

SECTION 2: HAZARDS IDENTIFICATION
Classification of the Substance or Mixture
Classification (GHS-US)
Expl. 1.4S

The safety data sheet for Winchester primers
http://www.winchester.com/SiteCollectionDocuments/pdf/SDS/PRIMERS%20%E2%80%93%20CENTERFIRE.pdf
U.N. Dangerous Goods Class
Explosive, 1.4S; Explosive, 1.4B

The safety data sheet for Remington primers
https://www.remington.com/sites/default/files/documents/Final%202_CFSSPRIM.PDF
Section 14
14.3 Transport hazard class(es)
DOT UN0044 Primers, Cap Type 1.4S

So I think we're good up to 150K now.

A lot depend on what laws (and regulation) your state may have adopted.

Neither SAMI nor NFPA are 'laws' but are designed to serve as a basis for states and localities to adopt.

Some adopt them as written many (even most) others make changes.

Be sure to also check under 'administrative codes' if your state has them.