Whoe guys.
As the moderator of this forum, I think I need to interject with some advice.
First of all, Using sized or fired brass cases is not a safe or good way to set or check headspace on any gun. The CBA does not condone this practice.
Brass cases are too soft and the camming action of the bolt is very strong. Thus, you cannot reliably tell if the bolt is “just touching” the headspace gage. Buy a hardened and ground hs gage and do it right. They are not expensive an are ground to very tight tolerances. Headspace is a dimension on a chamber print (not a cartridge print) and is a nominal value usually plus or minus .004".
I just finished chambering a 22-243 barrel for a prairie dog gun and did away with the barrel nut. I just made a shoulder on the barrel stub to stop it at the correct distance from the bolt face and used a proper headspace gage to set the headspace exactly to where the gage can be felt slightly as the bolt is lowered gently. In other words, just as the bolt handle stub touches the side rail of the action as it locks into battery, I can feel the slightest resistance. That feeling is when the headspace is maybe .001 shorter than the nominal value of a go headspace gage. You have to develop a feel for it that cannot be felt with a cartridge case. If I want to check it another way, I simply put a small piece of clear tape on the back of the go hs gage that is one and a half or two thousanths of an inch thick and I have a no go gage. Just remember to take the tape back off. I use this method and it works for me. I would advise anyone else to buy a “no go ” gage if you haven't developed a feel for this.
I usually set the barrel stub length to clear the bolt nose by .010” and that has always worked for me. The more clearance you have, the more of the case sticks out of the chamber unsupported. If you get it too tight, it will definitely hurt accuracy and debris can cause problems closing the bolt. Check the clearance of the factory setting by closing the bolt on a piece of lead shot and then measuring it after it squashes down to the clearance. Make sure you lube the lugs so you don't gall them.
Using the barrel nut system, simply use a hardened HS gage and turn the barrel down till you “just feel” the gage and then tighten the nut. Sometimes it takes a few tries to get it just right as it's difficult to hold the barrel from turning toward or from the action while the nut comes tight. This system is really quite ingenious as it is quick to do in the factory and actually pre-loads the barrel threads up in the direction of the force when the gun is fired.
In summary, do it right and be safe and accurate. If you don't completely understand what you are doing, take it to a professional. Check the chamber for debris every time you use the gage. Look in there with a good light every time. I've seen guns blow cases that were headspaced by somebody who didn't know what he was doing or was not super careful. Remember, you are placing your head inches away from a tube with 50,000 PSI in it!!!!!
Tom Gray