I lived in norcal a few years back and my .45 1911 was my standby.
I went to a local store and purchased 45 acp shells and didn't look at the box.
I went walking on my property and as my dog barked (I dismissed my dog) I was standing within 25 yards of a black bear.
I racked my slide and experienced my first ftf with my trusty Springfield 1911.
I chased the bear down the road, thinking I was safe...
I got back home and started investigating why I had a ftf and realized my local gun shop gave me 45 gap vs 45 acp...
I felt dumb to say the least.
If you force 45 gap, it will chamber into 45 acp...fyi
45 gap sucks, :)