Brass stretches primarily through the full length sizing process and simply has to be trimmed. Don't like trimming?
You have to if you're a handloader. Neck sizing only can prolong the matter, but you'll have to full length size eventually. Bump the case mouths in a sizer, just enough to straighten them out. New cases come dinged up from the factory. New brass doesn't always come from from the factory in uniform lengths. Just trim them all to minimum. Time envolved is a wopping 10 seconds per case after you're set up and running. Make sure you set your trimmer properly. It's really depressing to ruin 50 cases before you realize your mistake!
Then champfer and deburr the case mouth. Mandatory.
For you new handloaders: Where does the extra brass come from that makes the case neck longer? If you don't know the answer, you need to research it until you understand case resizing, case stretch, and head space.
What is an incipient (partial) case head seperation? It's a split (upon firing) at the web of the case because the brass has become thinner during the firing and resizing process. (The crack starts on the inside of the case and you can't see it) Guess where the brass went. Well, it went to the case mouth,that nobody likes to trim, and made it longer or thicker. If you've HAD to trim 4 or 5 times, you might consider that the limit and discard the cases. The brass has simply become too thin near the case head. You can feel the crack inside with a paper clip bent into a hook shape. You should keep a log and know exactly how many times a batch or LOT has been reloaded. When you learn how many times you can trim a case before cracks appear on the inside, then discard them just before you reach that point.
When a case is fired, the case expands tight against the chamber walls and forms a seal. Except for the thicker part of the case at the rear. There, it can only stretch backwards until it is stopped by the bolt face. The amount it has to travel to do that is generally referred to as the head space (not the technical definition). Too much headpace can cause a seperation, (it can only stretch so far without splitting), and so can normally safe headspace if the brass has become too thin there, as described above. If the shoulder of the case is set way too far back through improper resizing, then it can result in a catasrophic full case head seperation ALL of the pressure escapes into the action and can blow up the gun and the shooter. The safety vents can't handle that much pressure.
NOTE: UNDERSTAND the concept of full length resizing! As in: Just enough for the case to fit your rifle so as to reduce case stretch upon firing.
The less serious, but still dangerous, partial head case seperation amounts to a crack all the way through the case where SOME of the pressure escapes into the action, and escapes out the vents on the receiver peppering the shooters face and shooting glasses with powder residue. Can draw blood. Or cause eye damage if shooting glasses aren't worn. Gun damage usually results in a ruined extractor on rifles like the Rem. 700, but usually not more serious than that. Remember that we're dealing, typically, with 50,000 lb. per sq. in. or more of pressure (PSI).
It concerns me when shooters jump into hand loading without learning the basics first, and when they take advice from well meaning, but not necessarily knowledgeable, fellow shooters. Many shooters on the board are very knowledgeable, and some aren't. Be careful.
