How long can ammunition be expected to sit on the shelf before it can be considered no good?  Specifically carry ammo.

if cool and dry over 20 years maybe 50.  hard to tell.

With the exception of the lead free primer target ammunition, the shelf life of ammunition stored under good conditions is so long that we mere humans don't have to worry about it.  I doubt your young children will have to worry about.  Even their grand children may not have to worry about it.

Smokeless powder samples from 1895 have not deteriorated yet.  WWI era brass cartridges used to crack at the neck after a few years, but annealing has remedied that.  Primers are sort of the weak link, the lead free primers are not good for long term storage.  The old corrosive chlorate primers were the best, but even today's non-corrosive primers last a long, long time.

About 1979, I fired a .38 Spl cartridge found in my grandfather's desk.  (He supposedly never owned a pistol, go figure!).  It went bang on the first try, and I was surprised to see a big puff of white smoke.  Yes!, it had been loaded with black powder, and was probably 75 years old at that point, (maybe less, maybe only 25).

I have fired some of my reloads over 35 years old, no problem.  I have fired lots of 50 and 60 year old surplus ammo over the years.

Now, some times ammo is stored in bad conditions.  Too much heat is bad, and oil vapor and fumes are bad.  I have a few WWI era .45 ACP cartridges upstairs.  I bet every one of them would fire.  I saw a video where a guy tested some similar cartridges, and compared them to modern day production.  Reliability of both was 100%.  The old stuff some times had a barely perceptible hang fire.  It was slightly lower velocity with a slightly higher standard deviation.  The accuracy was slightly worse.

Still pretty good performance for some thing that old.  Nothing to stand in front of.

manufactured today   100 years

Modern ammo a couple of generations easy.

Good to know.

We get issued fresh carry ammo every six months, for whatever that's worth.

I have fired ammo that is decades old, but I'd prefer more recent manufacture for defensive use or important hunts.

I like other have shot ammo many decades old.  I have shot my dads reloads from the 70's

Your lifetime and then some.

Agree. I've fired .45acp milsurp that was 50-60 years old with no problems. Part of its life was in a dresser drawer, and part of it was out in a cabinet in a ramshackle barn; don't know how long in each, but a half-century or more in all.

Also +1 on the potential timeframe limitations on the lead-free stuff. I accidentally picked up a couple cases of the UMC 'Leadless' stuff this year and made a point to go ahead & rotate it into use ahead of where it normally would have been.

Hard to say.  I'd start to get concerned around 50-60 years.   With reasonable storage, 200 years or so would be reasonable.  

Of course, I would expect bullet design to have improved by then.

Every now and then when I go to the range I pick up a handful of steel .45 acp cases with head stamp dates back in the 1940's.

I don't know who's shooting up an old stash of steel cased GI ammo but if they're not cleaning that gun after each trip I hope the stuff ain't corrosive, like some of the WW2 ammo was.

When I get a box or so of that brass (have 30 some casings now).  I'm going to buy a box of 230 grain FMJ bullets, some Winchester large pistol primers and load me up a box of "fake" GI surplus ammo to keep with my old 1911 Colt.  Just for a conversation piece.

Agree with the previous replies stating not to worry.

One thing that I might add, in the context of carry ammunition,  is that you'll probably replace the ammo due to a newer design coming out than to concerns over the ammo's age.

I have a couple boxes of 20 year old hyrda shok that I'm fully confident will go bang. I don't load this ammo in carry guns anymore because I switched to HST some years ago, not because it's too old.

In 1980 I loaded 100 rounds of .45.   No frills, no case-sealing, no special treatment,just range fodder.

In 2003 I discovered those 100 rounds in a closet.  I took it to the range.   100 bangs, 100 cycles, 100 holes in the target.  That ammo could have been loaded the weekend before, but it was 23 years old.

The Swiss GP11 ammo I'm currently shooting in my K31 and G1911 is dated 1978. It is the oldest noncorrosive ammo I can verify the date on that I have. It goes bang with each pull of the trigger and is wonderfully accurate yet.

Good quality ammo stored well will last a long, long time.

Still shooting stuff, made in 50s.

One company states 40 years.  That's actually a conservative estimate.

Modern powders are quite stable and modern primers, while not quite as long lasting as older corrosive compounds are still going to hold up for at least 40 years, even under less than ideal storage conditions.

Keep the ammo dry and avoid extreme heat (over 100-110 degrees) and it will last longer than you will.  

GI surplus ammo cans work great for storage, provided the rubber seal and hinge pins are intact.   We took 4 ft of storm surge in our walk out basement during Irene, and out of the several thousand rounds of ammo I had stored there, only three boxes got wet, and they were stored in a an ammo can with a missing hinge pin that consequently, leaked due to a less than perfect seal.

I have M1 Garand 30-06 that shoots just fine after 70 years.

The problem with trying to determine the long term life of anything is that a significant quantity has to be stored for twice as long as the 'age'
you are trying to demonstrate.

Back in 2002 or so, I shot 1 mag full of .45acp ammo from 1917.  It was kind of dirty, but it shot just fine.

Not too worried about the ammo I have stored away in cans, that stuff ought to outlast me. My carry ammo, I change out when the clocks change. Heard once that sweat and being that close to your body can affect ammo and for the cost of couple boxes twice a year, its worth it.

Store in a cool dry place and above average quality ammo will outlast you.

I have ammo from 1938 that I've shot in my Steyr.  No problems, other than corrosive.

About two years ago I acquired some ammo from a pawn shop that had been traded in with various firearms. In the lot was a box of Peters High Velocity Rustless .22 LR ammo. Out of curiosity I decided to see how old it might be.... I found the box on a collectors website and it said that box was used from 1932-1934.

There were 30 rounds left in the box.....I shot them all at a steel plate out of a Ruger MK II pistol. Every one went bang and cycled properly, they all hit the plate. I have no idea how the ammo was stored in it's 80 years of life....but it all ran fine.

About 6-8 years ago there was a bunch of USGI .45 ammo that came into the country from Russia- either Lend Lease or Recapture stuff from WWII. I bought a couple of cases, it was dirt cheap as it was corrosive. Ammo was 65-70 years old. I shot every round of it without any issues. That stuff was made during wartime- who knows how it was stored in all the intervening time...

Ammo produced today, given good storage should easily last 100 years and still be effective in my opinion

That.  At least several decades.

What do you mean by shelf life? If it will go bang, probably for a century.

Now how long it will maintain optimum accuracy?  Powder does deteriorate slightly with age and I wonder if it will go bad at different rates in different rounds - just a little off means it's no longer match grade ammo.

I shot a shit ton .303 and 8mm that was head stamped early 1940's in the early 2000's

Duty ammo? I shot an entire box if Ww2 .45acp five years ago. Not one dud - so that's what? 60 years?

I just fired 30 rounds of .38special 158Gn LSWCHP (+P) that i was given in 1994. all worked fine.

The only problem i personally have had with old ammo was misfires with Federal lead free primers after the ammo was about 10-years old. I'll never knowingly buy ammo with lead free primers again.

up untill recently the ONLY ammo available for the 8X56R was NAZI surpluss ammo. It had been stored in God only what conditions and always went bang. I think cartridges from the era of the very first cartridge ammo are still shootable.

I shot some 8mm from the 1890s and it worked fine & didn't group badly. So if it doesn't get wet, at least 120ish years.

Kept cool, in a sealed metal  box, with dessiccant.... probably several centuries.

So what about improperly stored? Say, sitting in a dresser drawer?

This, even longer... if it's stored high and dry your great grandchildren could use it.

Still shooting WWII surplus 30'06

Stored cool and dry it will last a lifetime and more.

How humid is your house/area?  Is it in the same area/room as a hottub?  Humidity is what kills the ammo Faster. more humid, The quicker it will deteriate, Dryer the conditions will allow it to last longer. More than likely it will still go bang, Your accuracy/dependability will suffer.