i second destructo6's recommendation re locking shoulder and headspace issues. save yourself the headache (unless you are mechanically include, have the right gauges and micrometers, etc).
"...and which is worst of all, continual fear and danger of violent death, and the life of man, solitary, poor, nasty, brutish, and short."-Thomas Hobbes, Leviathan
...What he meant to add was, "unless, of course, all responsible citizens are armed to the teeth."