First, are you using a magnum case or standard bottle neck case? Headspace is different on magnum, they measure on the belt. Bottle necks measure from base to datum line (about half way up the shoulder). When you turn down the bolt, is there stiff resistance? If so, you probably need to bump. Try to bump a minimal amount, not more than .003". Deprime the case, put the empty in the chamber. First remove firing pin if you can. If you feel hard resistance, turn your F/L die down a quarter of a turn at a time, keep resizing and turning down a quarter, until the case chambers with just a very small resistance. That tells you the case shoulder is touching the chamber shoulder and is just right. Going further creates dangerous excess headspace, and other problems as well.
so there is a way to check it and how do I check it what about putting a little clay on a vergin round chamber it (dont shoot it) pull it out and mic. it see were I am at now clean it off (shoot it) and recheck the case and do the math would that give me my head space ( I biuld car motorcycle HD engines so I got all kinds mic inside out side mics. and things for getting things with in .001
"Try to bump a minimal amount, not more than .003". Deprime the case, put the empty in the chamber. First remove firing pin if you can. If you feel hard resistance, turn your F/L die down a quarter of a turn at a time, keep resizing and turning down a quarter, until the case chambers with just a very small resistance."
Gene, your idea is correct but your suggested adjustments to attain that .003" bump are off. Dies have 14 threads per inch. A quarter turn changes it a tad under .018". The .003" change you accurately suggest would be lost some six times in a single adjustment, moving the die a one quarter turn can take a case from not quite enough to way too much shoulder set back, aka excess headspace.
My suggestion of a 1/16th turn covers almost .0045" thou, so even that is way more than would be ideal to attain a shoulder set-back of 2-3 thou. But it's closer!
I move my size die in even more tiny increments once I'm within maybe 5-8 thou from where I want to be.
"...so there is a way to check (headspace) and how do I check it..."
CVA, the clay should get you close, but why care? There are no tools to do that because few care. All we really need to know is how to resize our cases to fit our rifle. Even precision riflesmiths don't much care about the absolute figure, they only care if the chamber headspace is within the normal +/- specs. They confirm it with a simple, two item set of "go/no go" gages.
"until the case chambers with just a very small resistance. That tells you the case shoulder is touching the chamber shoulder and is just right. Going further creates dangerous excess headspace, and other problems as well"
Not sure I understand this idea either....dangerous if you don't have resistance to closing??? Maybe some others like resistance to chambering but....not me...not for my hunting loads.
Boomtube, you are correct; I did not give much thought to that statement. And I don't turn em down a quarter turn myself. I turn the die down just a fraction, try and if not enough do it again. There is a need for someone to design a shoulder bump measurement tool. You can have your gunsmith make one; think I paid $60 for the last one in 30BR. Harrels includes them (some guys call them a "thingy") with every new F/L die they sell. But, I have trouble getting consistent readings with it. The idea is you put a small thimble over the case mouth so that it touches the datum line (center of shoulder) , then use your calipers to measure base to the top of thimble before and after bumping. But this is real tricky. I have used a 45 ACP deprimed case to do this, but it is not much better.
Headspace is probably THE MOST important dimension on a case and chamber. There is nothing futile about headspace measurements.. Maybe for someone who knows what they're doing on they're rifle then it is an 'understood' issue. To this person, it is futile, but never forget, if you inadvertantly over bump or over size the case body, and forget to check, then uh-oh. I will do a check on headspace with a vernier micrometer and will check before neck sizing, usually they're tight at around +.002 to.003" over ANSI/SAAMI, there is a range of about ten thousands of inch, but this check just lets me know where I am in the case lifespan, and if I do bump the shoulder, I have a reference point . .