re: Advice on Breaking in a S&W 40 cal Shield Needed

Any new semi I like to shoot 50 to 100 rounds at a time at first, until about 500 rounds are through it. Clean and lube every time home from the range, no exceptions.

You want to record any ammunition or operating problems during the period, in case you have to make a warranty claim - as well as figure out what ammo it likes best.

After the 500 are through it, you want at least 100 rounds of your preferred carry ammo through it - with the magazines you intend to use as primary and reloads. The tolerance for failure for 100 rounds is exactly 1, no more. As soon as you get the second failure, assuming there is no other issue, re-evaluate your choice of carry ammo, pick another one and get 100 rounds through it, again, tolerance for failure is exactly 1 (this assumes you are using name brand domestic or high quality foreign ammo, that has no known significant issues with your platform).

That's my break-in procedure.