"Colt Super .38 Automatic" , as it says on the slide. The s/n is 57XXX
I think you have a vintage slide on a knock-off receiver. I don't see any Colt marks on the frame above the grips, nor do I see a Colt s/n on the frame. If you can, post a clear, large, detailed pic of the right side of the frame visible (leave the s/n intact or if you feel the need, x out only the last digit or two and nothing else).
The problem is:
1) lack of Colt markings on frame
2) your stated s/n is not compatible with pre-war commercial Colts (should have a prefix)
3) your s/n is not compatible with a Colt military frame with those 1911a1 features (would be a 1911 frame, not an a1)
Also, the fact it has military contract grips on it means it has been altered at some point in it's life. Unless an alloy frame, the frame/slide finish should age identically, and those are slightly different. A confusing thing is it looks like the small parts on the frame are correct to a pre-war Colt. Seeing better angles on the MSH, trigger, and detail on the slide stop would help make sure. So maybe it was a rebuild on a non-Colt frame for a gun that had a frame failure at some point? Just a guess as a possible explanation, trying to come up with the simplest explanation for what you see is usually the best answer.
I bet it hasn't had a box of ammo through it in it's life.
The slide at least has had much more than that through it. The wear on the dust hood clearance cuts on the slide means that girl has been making quite a few cycles. Commercial Colts of that vintage were usually fit tightly enough at the factory that wear like that did not occur; which is another thing that makes me think the slide is not original to the gun as a factory unit, regardless of the markings.
I would say if the gun is mechanically sound and the slide/frame and barrel are fit really well, it might be worth $500 to $600 as a shooter to someone who really wants a .38 Super.