I've got a 9mm p94.  Can i throw a 40 sw 94 slide assembly on that frame and have it function correctly?

That swap sounds better than some I have heard in the past.
If you have the owners manual handy, check the part numbers on the ejectors (9MM vs. .40)...that would be one clue.
Of course, magazines, even though close looking, may not be totally reliable, if the "conversion" made it to that point.
I wouldn't run out and buy a slide assembly, but if a good friend had one to try out, I would go that route first, testing functions before even loading up a mag full.
Final answer...interesting, but I don't know.

Sounds good, i'll check that out when i get home.  I beleive my buddy has a 40 cal 94 so after i check the part numbers on the extractors i'll see if his slide fits and functions.

Ejector...the part you have to flip forward to disassemble, is what I was refering to.
I know Ruger wouldn't approve.
I have swapped lots of parts on like models of the same calibers. Taking a blue MKII .22 and swapping just the little parts with a stainless gun or using the most accurate barrel from several P-89s to build a keeper.
I never swapped slides from one caliber to another. Good luck, be safe and fill us in on your results.

ejector, sorry, I wasn't paying attention. yeah I'll definitely let you know how it works out.  thanks very much for the information.

Kyle

I've always wondered this too.  I would think it would be possible.  I'm sure Ruger wants to "fit" all slides to frames, but if the ejector is the same, it probably could work.  To be safe, you better call Ruger, although I doubt they would tell you that it's possible for liability reasons.
 The elevan round .40cal preban magazines (P-17) are less expensive than the P-18 preban mags (9mm) too.
The problem, if this would work, would be cost.  It's not just a barrel swap like a .40S&W to a 357SIG, it's the whole "upper" as you describe.  Since Ruger P94s are relatively inexpensive guns, the cost of a conversion would probably be 1/2 to 2/3rds the cost of a new gun in .40S&W.

I too have HEARD 'Ruger' wants slides "fitted" when change happen's, to both same calibers as well a task like this.