1911 Quick Check-Up
I'd check the sear/disconnect (not sure of the technical name):
1. Make sure there is no round in the chamber and no loaded mag, then rack the slide. Double check; a mistake here will cost you your hand.
2. Then, holding the gun with your regular one-handed grip, push the slide a 1/4-1/2 inch backward with your other hand, thus taking the gun out of battery.
3. Then try to fire while you are holding the slide out of battery.
If it fires when the slide is out of battery, the disconnect is not functioning properly. If that's the case I'd consult a gunsmith or one of true 1911 experts on this forum. I know a bit about 1911s, but I am not an expert.
I'd also test the grip safety"
1. Make sure there is no round in the chamber and no loaded mag, then rack the slide.
2. NOT using a normal grip--but gripping it any way you can WITHOUT depressing the grip safety--point in a safe direct and pull the trigger.
If it fires without the grip safety being depressed, consult an expert.
I hope your new-to-you 1911 passes these little safety checks.