This last week I was reminded of why we should do a functions check anytime we change something on a firearm or anytime we take the firearm apart. I had reversed the magazine release on a Glock and reassembled it. I did make sure the magazines seated in it and could be released afterwards. After going to the range, I found that the slide would not lock open on empty. When the magazine was empty it should engage the slide stop and lock the slide to the rear and it was not. This was a step I skipped during the functions check.
The rule of thumb is anytime that we change a part on a gun we should do a functions check after reassembling. Make sure the safety works, the action moves back and forth freely, it fires when pressing the trigger, the trigger resets, and the action locks open on empty etc. This goes for both handguns and rifles. This should also be done anytime we take our gun apart such as when we are cleaning it as well. This will indicate whether the gun has been assembled wrong or whether a part in the gun has failed or has worn out. Also inspect things that take batteries to make sure they are still working properly and there is no corrosion occurring from the batteries.
Have a good weekend!