I put a norinco in a wood us GI stock and the mags. won't lock in. Put it back in the original chinese stock and they lock in fine. What could be the reason? Mags are both GI & checkmate.

There can be a couple of different reasons for this problem. In general the Chinese M14 should fit, sometimes you have to make some adjustments to the stock. How was the trigger guard/trigger group lock up? In addition, can you do a function check of the rifle without the mag loaded?

The lock up seemed OK, it snapped right in. The mags won't roll back enough to lock in.

GI mags lock up fine in my Poly in a GI synthetic. The Korean
mags take a little extra effort, but do lock.

Make sure your weapon is clear, then cycle bolt to the rear and release into battery. Then pull the trigger, and repeat the bolt cycle to see if the hammer follows. The problem can be, something with your trigger group, op rod guide, or relation of your receiver to trigger group (height). There is a measurement (spec) but unfortunately I dont know what it is. You could probably google m14 stock fitting? This likely the issue.

The Chinese made guns have a shorter connector lock pin, which the Chinese stocks are cut for.  USGI stocks are cut to fit the longer connector lock pin that US made rifles use.  The extra gap causes the pin to work loose, and when that happens the operating rod spring guide slips out of position and the mags won't lock into place. The connector lock pin holds the spring guide into place.
If one uses a USGI stock on a Chinese rifle, one must either replace the connector lock pin with a USGI pin, or use some form of spacer glued into the stock where the pin is.  A piece of popsycle stick works well.  One can use that, or a use a small blob of epoxy. If one chooses to replace the pin, the USGI pins are a very tight fit, unless they are polished to remove the parkerizing.