I have a G27, wife has a G26, went to the range yesterday and fired maybe (5) 9mm rounds through my 27, it was not cycling the action, I thought we had a bad batch of 9mms then realized what was happening. Should I be looking at anything in particular for damage from this?

just look down the barrel when you disassemble(sp?) it. check to see if the rifling is intact and doesn't have any flat spots, which i doubt it will. otherwise, i wouldn't worry about it. remember, it's a glock, and their pretty darn tough.

Good God...  

Uhhhhhhhhhhhhhhh I did the samething.
put a 17 mag in my 22 . man that thing sounded funny!

No harm .

You were lucky.  During range qualifications for work last year another officer got a 9mm round in his mag.  Fed it into his 22 and fired - the spent casing failed to eject.  He manually racked the slide - without removing the mag first - and managed to push the casing for the 9 INTO the barrel with the next round.  Beat the casing out with a cleaning rod and a mallet and finished the qualify.  Ended up buying a new barrel.

Dave

If you look at the primers of 9mm cases fired in a .40 cal pistol they very often show pierced primers. So look for any gas-cutting on the breech-face. 6 rounds very probably did not harm your gun but since a 9mm case is quite a bit shorter than a .40 it means only the extractor was holding the round in the chamber.
Inspect the cleaned barrel's chamber and be sure a good .40 round slides in and doesn't catch. Finally just an FYI: Since the 9mm case can not expand and seal upon firing the gas if free to be forced back into the feed ramp, breech, etc. even into the striker channel.
Hot gas at these very high pressure leves can really do a number on the best of pistols after XX number of rounds!  
There is an Idiot at a local range that consistantly fires 9 in his .40, would love to
tear his gun down and examine it!

i thought about what happened,now pretend its midnight,you hear a bump you grab your 27 and for some reason you have to reload what would happen if you mistakenly load her 26 mag as a reload hmmm scary.i faced this prob once but i live rural and was after coyotes not as deadly as 230 lb ex con but never the less we should ponder our defense tactics to include murphy.

I don't think there's ever been a combat/tactical situation that Mr. Murphy missed.  I plan EVERYTHING around him.

Krez:
Have you considered trading your 27 for a 26?  Then you both have the same weapons and everything interchanges.  Is the .40 that important to you?  Just a thought.

S&W figured it out years ago...the 4006 mags won't swap with the 5906.
After a good cleaning/inspection, "roadtest" to verify integrity and function.
Most likely it vented, not building up any significant pressure and the most damage would be just extra dirty.
Good question as it's best to be on the safe side. Glad nobody got peppered.
You may want to mark the mags in a more prominent way (maybe white enamel in the embossed caliber designation) or leave one or the other gun at home.

I have considered converting my G27 to a 9mm, the depreciation of a Glock is too great for me to just go and trade, I will probably receive half of what I paid if I trade it.

I would like to thank everyone who has taken time to respond to my question.

I have decided to put a plus one pierce extension on my Glock 27 so I can tell by feel and by sight which mag I am holding.