I've got Tenex from the 80's, never stored right (in my shop, freezing in the winter, 85-100 all summer) 1/4 of the bullets are loose in the brass case. Weird looking white waxy film for lube.
Still shoots a 3/8" ragged hole at 50 yards.
Yes, but it should be shooting 3/16. My experience with this issue is that only when you have a rifle and ammo combo capable of consistently grouping in the 2's will you be able to see any statistical change. I always kept most of my ammo in the garage. It would be 100F in the summer and sub-freezing in the winter. I could not tell a difference because the most accurate 22 that I owned struggled to group 1" at 50y even from a bench. The variance in the ammo was getting lost in all of the noise from other variables like a stiff, creepy trigger and a dirty bore, poor sights, etc. Then I bought a Winchester 52 and a year later a Remington 540XR. Both were sub 1/4" rifles with good match ammo off of a bench. I would test and search and found a lot of ammo that was shooting in the low 2's and high to mid 1's with the Remington. Great. I bought a bunch of it and left it in by garage for two years. Got it out and was dismayed to find that it would not group nearly as well or as consistently as before. Whey? Theory: "The heat of summer cooks off some of the chemicals in the propellant and/or primer mix. This varies from box to box and rd to rd and in some cases you get a slow round." The only way to prove this would be to chrono before and after. Just shooting it introduces all of the other variables in the gun and the shooter. Wind, eyesight, trigger pull, grip, etc. I am pretty sure that winter is less harsh on ammo but again, just a theory. I had some of the Federal Ultra dimple primer Olympic ammo from the 1990's. It was amazing stuff. But after 15yrs of storage in my home (not garage), it was barely able to group 1/2". Also, I think that carrying around match ammo for long periods in your car or truck is also a bad idea. There are wide swing heat/cold cycles and extreme heat at times. But most importantly, is vibration. I think that over time this can slowly cause some of the primer mix to crumble and fall down into the powder blend. There will usually still be enough wedged into the rim to still fire the rd when called upon but it might??? slightly slow the ignition and affect the velocity of the bullet. My theory. Yours may vary. The idea of conducting a semi-scientific study is interesting. The do so we should eliminate as many variables as possible. Take one brick of match grade ammo. Remington bulk pack is not going to cut it. Lapua, Eley, RWS. Anything else is BS. Fire a 6x5 challenge with it with your chosen rifle. Chrono the rds and score it. Then take two boxes and put them out in the garage or shed exposed to ambient temps for 1 full year. Place two more in the car or truck and place the remainder in a cool, dry, comfort conditioned space. After one year, fire a 6x5 using the same rifle under similar wind conditions all on the same day. Use the Chrono and measure the variance in velocity and SD, as well as the 6x5 scores. Use the ammo stored indoors as the control. Don't be surprised to see that it has deteriorated some also but not quite as much. I will predict that the worst ammo of all will be from the lots stored outdoors in your vehicles.
When I shoot precision matches, I always try to use fresh ammo that has been stored indoors and is less than 6 months old. At my club we currently have 6 of the top 10 ranked shooters in the nation in the ARA's new factory rifle class. This is one of the most level playing fields of all because it requires each shooter to use a new factory stock rifle valued at less than $1000 (rifle only), any optic and any ammo. A list of older mid to low cost rifles is also allowed. They exclude all of the Annies, the Rem 40x and mod 37, all of the Win 52's and 75's the coopers, etc. Some of my colleagues also store their ammo in a cooler so it will not change temperature from card to card. Does it help? I dunno. The five time national sporter class champion does not do it. But he also had a magic John Langley rifle with an Ekke (spell it) bbl. I am using a 50yr old Remington with a $300 Sitron scope and am among those top 6 using Lapua CX ammo. It is not my best rifle but is one of the best that matches the criteria. Matches are currently suspended due to virus limitations. Hope to resume soon.
