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I ask this as what I used to load is now markedly less in the the latest reloading data tables.
I used to use W760 in 30.06 pretty much to duplicate their factory load.
They still market it as W760 I had no problems with the weight charge I used.
Am I still good to use what worked previously.
I'm no expert and I'm sure some good folk on here will be along soon to help you out but I know when I changed batches of power there was a huge difference and I had to drop 2 grains of powder to get the same result as my previous load.
Loading tables have become more conservative, earlier versions of the adi book just gave bullet weight now a range of projectiles is listed with slightly different weights for each. I understand that monolithic bullets have different distortion and friction coefficents under acceleration so can understand separate data for them.
As to powder changes, they do occur as mnf is a batch process using cotton as a primary ingredient and with any natural material slight variations can occur. Processing and testing will keep these within tolerances set by the manufacturer but changing from one at the bottom of the burning rate spec to one at the top might show a variation.
Double base powders show less batch to batch variation compared to single base ones as the nitroglycerine added can be varied to fine tune the results along with the coating applied.
Different batches of the same powder can perform differently. If your old load was near max then best to back off a grain or two and work up load again to be safe. Powder manufacturers and plants seem to change hands quite a bit so depending how “ old” your old powder was it might be quite different with stuff being made & sold today. W760 and H414 both now marketed by Hodgdon were originally different powders, now a days same powder just different packaging. Be careful
Yes they do change. As others have said, there can be differences between batches of the same powder, but long term the powders can change too, and I'm not meaning during storage (though they change then too).
I found 44gr of AR2208 was too hot in my 308 back in the early 1990's, had really sticky bolt lift. Starting load was 41gr and 45gr was book max back then in Nick Harvey's manual.
Nowadays I'm at 45gr with no issues. New powder (still AR2208 though), different primer and case, but same projectile from same box, and same rifle. The ADI website has the starting load at 44gr and max at 47-47.5.
Reading this and other threads has been an eye opener for me. I knew that powders were not quite the same from batch to batch, but had no idea up until recently that the printed data was changing. I had previously thought of the data as something of an absolute.
Storage can be a problem with nitroglycerin tablets used under the tongue for angina - the volatile nitroglycerin content of the tablets migrated, so tablets and bottom and top had different potency, meaning a poor shelf life. Nowadays it is less of a problem with nitroglycerin tablets as they are individually blister packed.
If you have a double base powder (which contains nitroglycerin), consider shaking it up to ensure it's well mixed so the powder at top and bottom has uniform nitroglycerin content.
Interesting thread.
I'd just supposed there was a bit of variation from batch to batch, but didn't expect a permanent change over years or needing to reprove load safety or optimisation.
ADI states that "Bench Mark 8208 will maintain consistency from lot to lot, meaning that a load developed for this powder will need less tweaking." so it sounds as if there something to this and you might need to redevelop your load every now and then.