Gunsmithing AICS Chassis will not hold a magazine

[Pinmaster]

I picked up a used 1.5 AICS long action and it will not retain AI or Magpul mags. The release spring seems plenty strong. Even with the action out of the chassis the magazine seems too small.
Any ideas?

It also swallows AI 338 MAGS

 

[Rubicon Precision]

Try a CIP mag.