There's no answer to that question. Remember it's not the brass that you will run out of, it's the primers and powder. You can cast bullets out of wheel weights and reuse brass multiple times, but without powder and primers you have a poor club instead of a rifle.

 

Could not have said it better. The two key factors are the number of reloads per shell and the starting number of shells. Things that will effect case life are how hot you load, running through an action that tears them up and really key one that throws them where you can't find them. When doing my calculations I worked up the following table.

Loss Rate: 10%
Avail Total Total
brass Rds Reloads
Start 300 300
1 270 570 270
2 243 813 513
3 219 1032 732
4 197 1229 929
5 177 1406 1106
6 159 1565 1265
7 143 1709 1409
8 129 1838 1538
9 116 1954 1654
10 105 2059 1759

At a 50% loss rate you will get something like this:

Loss Rate: 50%
Avail Total Total
brass Rds Reloads
Start 300 300
1 150 450 150
2 75 525 225
3 38 563 263
4 19 581 281

At the 50% loss rate I quit calculating when I get below 20 rounds.

As you can see how many you start with and how well you can keep track of the spent casings is important.

 

If you dont load your rounds to 'hot'.. you could get 10 or more reloads from each one.. so 300x10= 3000.. make sure you have enough bullets (or the ability to make your own bullets), enough primers and powder to do 3000 rounds and your set. Of course you will want more than that on hand for reloading. but you get the idea of how much that will turn into as far as shootable rounds.

Of course some of the brass may not last that long and some will last longer.. thats just a rough guideline for you to go by so you can decide if thats enough ammo for you.. for a 45-70, unless that is your only rifle, that would be enough. but if its the only one you have i would suggest getting more so you can have more waiting to reload.

Ohh and if you do load the rounds hot.. you will greatly reduce the usable life of the brass.

 

Make sure you have a good supply of loaded ammo on hand too. All the reloading supplies in the world won't help if you are trying to load a few hundred rounds while the angry mob is outside your door with a battering ram.

 

I keep a lot of brass stored away. But as cranky farmer stated, it's no good without powder and primers. My general rule of thumb is to always have enough of the three Ps (powder, primers and projectiles) to reload whatever brass you have three times.

I would however, get as much brass as you can while it is still available and fairly inexpensive.

 

As much as you can store and afford? Is there ever too much ammunition?

 

Yep, once you have to hump it

 

What is your SHTF scenario?

 

As much as you can find and hide in several different locations.

 

In a post SHTF scenario you can reload your old primers.

In the second video the guy uses a star tip screwdriver. I think you'd get much better results using a flat-faced punch that just fits into the primer.

I wouldn't use my press as an anvil! I'd use a flat piece of brass bar or similar.

Instead of cleaning out the soot with a screwdriver I'd use a primer pocket brush for a more efficient clean.
Other than that the principle seems sound for re-using primers in a last ditch scenario.

Somewhere there must be a video that shows you how to make a rudimentary propellant - I know there are some for blackpowder. That'd be OK for bolt and lever action rifles but I'm doubtful it'd be a good idea for semi-autos - especially gas piston mechanisms.