Let me add....the attic is also a room in my house that I use. Sort of like my upstairs man cave. So the temps were always pretty stable.If stored properly, which that ammo wasn't, modern ammo is good for at least a lifetime. Ideal place is cool, dry, with limited temperature fluctuation. Your ammo is more than likely still usable, but I wouldn't trust it for hunting, on the off chance it has been compromised. 20 years of the extreme temp. changes may have some effects on ignition or accuracy.
Pop who is 88 now found an old side be side shotgun in the attic rafters of a friend when he was 10 yrs old along with paper wrapped blackpowder shotshells. Had friends uncle strap gun to a tree and tied a string to trigger. loaded and fired. Heard...click ... ...pop.... dink dink dink and OO buck balls roll down the barrel onto ground . fired all rounds with same results. probably turn of centry ammo when he did this in 1941I once bought a soft gun case at a garage sale. It had a zipper pocket and I found some 12 ga.paper cartridge shot gun slugs in the pocket. No idea how old they were. When did Remington Peters stop making paper shotgun gun shells? I was curios so I walked out to the range and fired one. Yup, it went off. Shot center at 50 yds. Kicked like a mule in my single shot Pardner.
Which caliber? The 7.35's are notorious for bad ammo, but not as common as the 6.5mm calibers.I bought some surplus ammo that was manufactured in 1936 for the Carcano just after such guns became famous in November of 1963. The stuff was awful! Some rounds went off when I pulled the trigger, but some rounds took 2, 3, and even 4 hits from the firing pin before she would bark.
It was 6.5mm. It's easy to remember because I still have the gun and still take it for a walk now and then. With modern ammo that carbine makes for a nice little brush gun and it's been responsible for the demise of a few deer.Which caliber? The 7.35's are notorious for bad ammo, but not as common as the 6.5mm calibers.