Al, I will address this topic. There is of course spring back when you fire a brass case in a rifle chamber, good thing too as if there wasn’t we would never be able to extract the shell from the chamber. In the resizing process we deal with the expansion of the brass from the firing, the spring back is so small that the Brass still does need resizing though. What we do when we resize a case as compared to a case being fired in the chamber is insignificant. Now with that said there is a small bit of spring back if you do not let the case “REST” in the die for a moment. Wynne is correct about 10 seconds seems to be the correct amount of rest. I do leave mine in the die longer as I use that time to clean the primer pockets and de burr and chamfer the necks for the next piece of brass.
I have measured brass so many times and in so many ways that it is not funny. To get a correct, or maybe I should say accurate measurement you are going to have to use an accurate tool. 99.9% of all reloaders will use a Dial Caliper for this purpose, and I say with no reservation, that if that is what you are doing it is almost a waste of time. Dial calipers are just not accurate enough to measure even at .001 and certainly not any smaller than that. I have dial Calipers made by the best ==Starret, Advanced Scientific Measuring Tools, A-Tec, long Island Indicater Service there prices run from a couple of hundred dollars to a $1,000 a set. Luckly I didn’t have to buy them myself. None will measure to a “CONSISTANT” .001 each and every time. As a matter of fact you can measure the exact same piece of brass 10 times and come up with 6 different readings using a Dial Caliper. I say this for some “JOBS” there are times when a Dial Caliper is the right tool to use, looking for a .001 difference on a piece of brass is not the place for them.
If resizing a case is done correctly, the difference is so small as to be of any worries at all. Benchrest shooters especially 100 and 200 yds are known for tuning there loads at the range thus the load at the range and do not pre load for a match. I know at least a dozen very successful shooters who have 30 to 40 firings on there brass, and not a single case has ever been annealed not once. If brass gets so work hardened that it will not resize due to spring back it would have split long ago.
I was at one time a big advocate of annealing brass. Even bought a Machine a Bench Source Annealer for this purpose and still have it just don’t use it very much. I was a firm believer that annealing after every firing would make my brass more consistent. So I put this theory to a test. I took 50 cases and annealed them after every firing, at the same time I took 50 cases and never annealed them at all. I always judge my results from what I see on paper, after I had 30 firings on all of these 100 cases I observed there was absolutely no difference on the target not in group size or in score NONE.
Another observation I made was one of the best pieces of advice I have ever received was to leave the brass in the die for a period of time to let it relax and thus conform to the die. Once I started doing this one simple thing the amount of pressure ( measured with a setting pressure gauge on my press ) became extremely consistent.