Take a slide from a functioning M1911 and put it on your gun. This will allow you to say definitively whether the problem is in the slide or the frame.
If it is the slide then:
http://www.ventureairsoft.ca/item.ph...ca74141527311f
Or you can convert your M1911 to a 4.3:
http://www.ventureairsoft.ca/item.ph...658a21fb96c890