Sig Compact Failing to Return to Battery on Last Round of Magazine

[MemLaw1234]

Hi, guys. I bought my first 1911 recently, having been a Glock guy for years. It is a Sig Revolution Compact C3 (officer frame/commander slide) alloy 1911.

I shot the pistol today for the first time and put 200 rounds through it. I cleaned and lubed it prior to shooting it, and I used only the two factory magazines.

About half the time, the slide failed to return to battery on the last round of the magazine. This only happened on the last round of the magazine, and it happened with both of the factory magazines.

Any ideas on why this is happening and what needs to be done to fix it? My first thought was the magazines, but it seems odd that both brand new factory magazines would be causing this.

Thanks in advance for your help.

[MemLaw1234]

To clarify my original post, the slide is not locking back. It is going part of the way forward, then stopping. Sometimes it goes farther than it does other times. Sometimes the last round is partially in the chamber after this happens and the rest of the time it's just sitting in the ejection port on top of the magazine where it will just fall out if you pull back the slide and turn the pistol upside down. I guess you could characterize it as the last round in the magazine not chambering or not fully chambering.

Thanks for any suggestions that you may have.