There were two parts to this.
There was a "Robust-Ideal" low cost model first (in the 30s IIRC) and then the monoblock construction of the Robust was generalized in the 70s I believe.
I don't have my Mournetas handy, but it is well described in it.
Another option would be that the gun would have had issues along the way (such as being buried during WWII) and somebody sleeved it.
More info on the model would help.
I don't think that the "single digit grade" Ideals would ever have that "feature" from the factory.
Best regards, WC-
Here is a link to the gun:
http://www.naturabuy.fr/MAGNIFIQUE-FUSIL-MANUFRANCE-IDEAL-CAL12-item-2133233.html