Brass storage affecting brittlness?

[skin]

 I found a brand-new bag of win brass in my closet in the house. I found another out in the non-climate controlled garage. Bought both of them at the same time, about 10 years ago. Same lot number. I decided to load up both bags. Started with the bag from the garage. Had two split necks in the 20 that I resized. Switched to the bag from inside the house. No split necks. The only difference between the two are the hot and cold cycles of the one bag. Wandering if that's enough working of the brass to cause cracks? Never had split necks from new brass before.

[SI VIS PACEM PARRABELLUM]

Are the cases discolored or corroded in any way? I'd keep the bags separate for the time being and size them that way. I have a couple thousand .38 spl cases that I have been loading and reloading for over 20 years without issues. Prior to that they spent 25 years stored in a garage loft that was hot and muggy in the summer and freezing in the winter.
A couple bad cases could mean nothing but obviously if 2 turns into 200 there's an issue.

[skin]

 Original unopened bags. I'm going to anneal the rest.

[Wobbly]

Besides the thermal, there are a lot of chemical interactions you also can't see.

For instance, the garage could have (at one time) a bag of fertilizer. Innocent enough, but the ammonia in the fertilizer can also attack the brass. The bag was not sealed against thermal attack, who's to say it was hermetically sealed against every chemical in a garage setting ?

 

[Radom]

Besides the thermal, there are a lot of chemical interactions you also can't see.

For instance, the garage could have (at one time) a bag of fertilizer. Innocent enough, but the ammonia in the fertilizer can also attack the brass. The bag was not sealed against thermal attack, who's to say it was hermetically sealed against every chemical in a garage setting ?

 

I would suspect this is the underlying cause: some sort of chemical reaction, or just a bad production lot.  Several of us here have noticed variations in Winchester bagged brass over the years.  I believe armoredman has run into this several times.  I did once with new 10mm cases.

I have stored dirty, once-fired brass in a garage or shed for most of my life without noticing any problems.  Usually these cases were in ammo cans or even just metal coffee cans. 

I'm not saying it wasn't caused by temperature, but that would make it a bad production lot by accepted industry standards. 

[M1A4ME]

My attic gets pretty hot in the summer (110 to 115F on a really nasty day.  Takes your breath away to walk in there.  My wife has dug her Christmas decorations out in December to find candles melted/sagged over/bent (no idea how hot candle wax has to get to sag/mush) so we started storing the Christmas decorations under the house (that's no fun getting them out and putting them back every year.)

Anyway, on several occasions over the years I've run across ammo (my reloads and factory ammo) stored up there for 20 to 25 years and taken it to the garage to get included on the next range trip.  Shot it all up (all that I've brought down, still have some cans of .45 acp and .308 up there, somewhere) with no failures to fire and no cracked brass.

Now, about 7 or 8 years ago, I did have some old (reloaded in the early to mid 80's) .44 magnum brass crack when we shot it in the Dan Wesson.  I don't remember what brand the brass was.  I do remember it was loaded with W296 and 240 grain jacketed bullets.  It was the .44 magnum stuff, not the light/plinking/range fun reloads.  That would have been stored upstairs for 20 years or so, too.  Not sure why the .44 brass cracked and the .223 (much higher pressures) didn't.  Same for the .357 magnum ammo (factory and reloads) as none of it cracked when we shot some of it.