Call up Pacific Tool and Gauge and buy a go gauge for your particular chambering.
Then go on MSC Industrials website and order a spool of Starret shim stock in .001". It'll look like silver ribbon for wrapping gifts.
Pull your bolt and strip the fire control out.
then remove any plunger style ejectors and the extractor
the bolt needs to go into the action with no type of spring loading. Just the bolt alone.
Drop your gauge into a clean chamber. cut up some shim stock into tiny little squares that fit on the face of your bolt. use a dab of grease to hold them there. Keep adding them until the bolt just "sticks" as it attempts to close. Do not force it.
David's gauges (David Kiff, owner of PTG) are set to SAAMI minimum standards unless ordered otherwise. So, the way to read this is say your chamber is a go gauge plus three pieces of .001" shim stock. Then your headspace is "GO + .003"
Well within safe limits.
Typically, .006" is the most you want to go before you are technically out of H/S. The gun will more than likely function just fine, but you will experience some elongation of your brass in the web area.
I set all my chambers to a dimension of "GO + .001" That way I can be sure I am moving the brass the least amount while still allowing the gun to function.
It's important to ensure that all your brass cycles properly after you size it. Especially if the gun is on the tight side.
If your gun is long, just be conservative with your dies when you reload. Don't shove the shoulders back. Just do enough to promote smooth feeding/chambering/extraction.
All there is to it. the gauges cost 29 bucks a set. They are precision instruments so don't be clumsy and drop them on a hard floor. Nicks and dings will give you false readings.
Hope this helped. It's worked great for me and I've been lucky enough to build guns for folks that have won in world 1000 yard events so I gotta be doing something right.
LongRifles, Inc. (coming soon!)