First time you have to carry and shoot it, you will wonder where it's been all your life. All those individual roll mark Colts are probably the last...
And that really is the only "is it time to start shooting yet?" litmus test we have. Which is why it's been gradual rather than the "big round up."
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I've got an old Burris Fastfire mounted on a Midwest Industries red dot mount which co-witnesses with the irons, and it's still working. Not the best...