TLDR: We have to give a rookie the best starting advice and let them develop. If they don't get started with learning to inspect their brass, they will never learn when a difference becomes big enough to flag it.
Since the OP is new, they will inevitably want to learn how sensitive they are in their own context to things like case weight and volume.
No need to confuse the thread with how case weight does or does not correlate to volume since you take the empty case weight to get the tare value when weighing the water-filled case. Any rookie who plans to shoot small down the road, had best get started learning what their components are doing as soon as possible.
Once you achieve your goals, it is often the case where you don't need to check things as often because you have already learned they are stable or don't affect you. You can then cut back on checking as often and maybe learn to spot check or just sample when new batches arrive. Till then... assume you will need to gather the skills and tools to inspect your brass prep.
It usually takes more than a 3 grain weight difference (within a common batch of brass) in something like a 5.56 case before we can see it on the target at 600 yards, and since that study has been run countless times there is no reason to confuse a newbie. He will need to decide for himself.
With studies of 556, 308, 30-06, etc., it has been fairly easy to show a good linear correlation between case weight and volume. The main point of dwelling on it for another minute is to say that the correlation coefficient does depend on having some significance in the weight difference before we would even see a volume difference.
In so many words, if you run a study and don't see a correlation, it is a good thing because that means your brass weight difference is likely in the noise and there is nothing to complain about.
On the other hand, if you are playing with mixed headstamp 223 or 308 brass for example, there is a fair chance you will eventually see a case weight difference, and that difference will correlate to volume. The real question then becomes is it important to sort out or can he even see it in his style of shooting?
A rookie needs to watch two ways. One is the big changes you can get when mixing brands of brass. A second way is to watch the difference within a common batch of brass. Those weight/volume changes are often different and may or may not matter to them.
If a rookie has a science/engineering background, we can speak about internal ballistics and sometimes we can show rough math to explain how things change with weight or volume. However...
While there is some easy math that shows how much of a bullet weight change is needed to see a difference on the target, there is no easy way to show how case volume affects velocity without resorting to complicated models.
That means details in brass prep that affect neck tension or case volume are better to test than to explain.
The OP will need to learn how much difference is too much and we can only share experience to suggest starting points. But first, we would need to know more, or at least I would....
In his post, all I know is that he is running a 105 grain bullet, but I don't think he has shared what cartridge he is running. If he did, I apologize for missing it, but that prevents a suggestion of when a weight or volume difference is too much and should be tested.
We might assume it is a 6mm, but if he wants better advice on case sorting, it would be good to share what case we are discussing.
If this is assumed to be a 6mm Berger 105 Hybrid, he doesn't need to sort bullet weight till he starts shooting Master or High Master at 600 or beyond because he won't see it.
If we assume a 6 BR variant, again, it takes a fairly big case weight difference before a rookie can demonstrate the difference at 600 yards, that is within a common batch. Change the headstamp and you should test.
Keeping his workmanship under control is important, and he should learn to track the vital stats on his components but not dwell on them too much till he gains experience. Learn to inspect your brass and track the vital dimensions. If you don't, then you will never learn.
When a new batch of primers, powder, bullets, or brass comes along, it should be at least roughly checked to see if there are any significant differences. It takes getting started with that discipline early to have a chance of learning when it is important later on. A rookie who plans on being good, should keep detailed load diary notes, as well as shooting climate notes.
A rookie needs to learn to set their own first order tolerances and goals. I recommend the OP measures his workmanship and includes a sample of his lightest and heaviest brass, and checks the volume too. That way, when he tests he will know if he can even see the difference. Carry on. YMMV
