Holdopen after last round?
 

Love shooting my new 1941 mismatched mongrel. No fails to eject or feed but doesn't often lock open after last round. What are usual causes for this? I keep well-oiled. Thanks for your help.

There are various. A chipped hold-open, Magazine button not engaging properly.

The majority of hold-open issues are magazine related.

Also check clearance inside the right grip for the mag button to move up and engage the holdopen. If this is suspected as the problem, try removing the right grip and firing the gun... if the holdopen works consistently without the right grip installed, you will need to do some minor inletting on the inside of the right grip to make sure it doesn't interfere with the mag button.

Now that is a nice added bit of knowledge.
Thanks
Jack

I have also heard that stronger mag springs help in some cases.

I have a mongrel that I love to shoot, but had the same problem. I noticed that the hold open was not quite as tall as the H.O.'s in my other guns, so I got one that was a little taller, and voila!