That's what I figured. Trying to narrow it down a little before I outlay $40 per mag.   thankyou for the input.

What aftermarket mags work best in the R I A  10mm.   Full size

Went to the range today after getting the weapon back on Tuesday
Gun performed pretty much flawlessly. All the spent cases I could find were good.
No mangled cases out of the 100 rounds I put through it .  Couldn't find a whole lot since they were Being ejected into low earth orbit .   RIA's customer service was great. Short turn around.   Tech note said they tuned it.   😬😬😁😬.  Happy and relived.  Looks like they put a new slide on it too.   

Pretty quick turnaround.   Gun is being delivered tomorrow.  We will see if she spits those spents correctly tomorrow .   Fingers crossed 

Yep that's what they looked like.  I'm not comfortable doing my own tuning.  I'll just wait till it comes back.  I've got a couple of boxes of sig ammo for it to eat when it returns.   Just hope it spits out the empties correctly

Unfortunately Im not comfortable yet with doing any of my own smithing work.  Thanks for all the info on possible fixes.   I knew going in the gun may need some tweeks  but Im going to give Armscor the first shot at correcting the issue.  I ve talked to a few guys at the gun shop I purchased it at and they had no problems with theirs right out of the box.   Excited about joining the 10mm ranks.  Especially after shooting it for the first time.  fun fun fun

Sellier and Bellot and then I put 70 rounds of sig ammo through it.

its going back to them.  Thank you for your input.  The ones that do eject properly fly a long way   

They are similar to this

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Well   Field stripped the weapon.   Brass particles everywhere.  Looks like the slide in scarred in a few spots and  heavy brass residue at the front of the ejection port.  did the tensioner test.  Not a lack of tension.   It will be on its way back to Armscor to see what its major malfunction is?  Hopefully it gets taken care of this time.   Miss it already :'(    Guess Ill have to shoot the 45 till its returns.

New to the forum.  Just purchased my first 10mm. A RIA Ultra FS in 10mm .    Took her out for a test drive the other day and only had one fte but had a dozen out of 50 rounds with the casings crushed at the top end.  I have read that others have had this issue and it was a extractor tension issue.   Should I give up and call Armscor and send it back or should I put another fifty of a different ammo brand through it and see if it continues.  was shooting Sellier and Bellot.   Gun was dead on and handled great otherwise.