I've checked the hole size against the FP from my other 1911 and have found the hole is too small for it.
I find this statement interesting, and if I were you, before modifying my slide, I might start a new post in hopes of finding out what the actual original 1911 spec is for the hole diameter. Then you would know whether the problem actually lies with the slide or not.
If you have no luck here, you might try a 1911 forum. Someone has this info.
I have no experience with steel cased ammo, as I handload my own using range pick-up brass
However, I have read of problems from the lacquer on steel cases (usually relating to rifles, but not always).
Please let us know what you find out.