[1]At least seven locking lugs....
[2]Why would you want to replace a perfectly good bolt?
- The two reliability tests started with bolts known to be crack free (all were NDI'd prior to test).
- The bolts were NDI'd every 6000, 8,400, and 12,000 rounds, most of the cracks found in these inspections were probably visible to the naked eye, and those that weren't were detectable under 10X magnification. Some of the bolts showed developed cracks as early as 6000 rounds, some of the bolts were still crack free at 12,000 rounds. Something I failed to mention was none of the bolts were removed just because they had cracks. Parts were removed only when they were the cause of a stoppage. And, those bolts with cracks detected at 6000 round when on to shoot 10,000 or 12,000 more rounds before they were pulled. Also, there were no rifle casualties, ie, non of the guns "blew-up"...
I am fairly confident that even if you crack a lug around 5000 rounds, you can go another 10,000 rounds before it becomes a reliability issue (unless you like to shoot really high pressure loads +62,000 psi).
So, if you feel that you just have to replace bolts on a regular schedule, replace them when the barrel is shot-out.
(Oh, and I replace springs only when they are below the minimum length. For pistols that I don't have technical data on, when they are about 1/2 inch shorter than they were when I got the gun....I haven't had to replace many springs.)
Cracks, you are looking for something like this:
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