Re: How "important" are certain details when reloading?
Crimping DOES affect accuracy because if you experience bullet setback it will affect accuracy and possibly safety.
That is why a lot of factory ammo is factory crimped.
If you carry ammo to the range in a plastic ammo case and load the rounds one at a time like benchrest shooters do, then no chance of recoil affecting the seating depth and alignment.
For those of us who hunt with several rounds in a hard recoiling rifle, a factory crimp is a good idea. Magnum rifles with short case necks are the most at risk.
The amount of crimp applied to the neck varies with case trim length. It's usually best to trim just under max case length when factory crimping.
Compressed powder loads also push outward on the bullet. Good idea to factory crimp those rounds as well. A hard push in a high vibration environment tends to move things around a bit.
When pulling lots of bullets that has been loaded for several years, it's amazing how much difference in force is needed to pull the bullets. Some bonding ocurs between the two metal surfaces, and it is not consistent round to round. If you had pulled as many hundreds of bullets as I have done, you would know this for a fact. A factory crimp is a more constant force to overcome, and tends to swamp out the metal bonding force to some extent. This is another thing that factories know and another reason they crimp. On quality Nosler ammo, they will probably leave that to the customer to apply the amount of crimp they want, if any at all.
If I buy cheap ammo for the brass, it is shot straight away with no crimp applied; otherwise, it goes straight into the Lee crimping die. A perfectly round factory crimp that I apply, with the case rotated 45 degrees and then crimped again to remove the 4 little crimping marks at 90 degrees from each other, applies a gas tight seal to the round. Hardly any use to apply sealing compound to bullet and primer if primer pocket is clean and tight and the bullet is factory crimped as I do it.
A factory crimp works on bullets without a cannelure, or with a cannelure. It is considered mandatory on ammo loaded for semi-auto rifles. If not considered an accuracy issue, it is still a safety issue.