Hello Wolf308,
I don't know about the rifle doing this, but I think it has a free floating firing pin which might cause this with sensitive primers. CCI makes a No. 34 primer which is made for semi and automatics. It is harder and should not slam fire. Stay away from Winchester primers as these are sensitive and have been know to cause slam fires.
Grafs and Sons sells boxer primable cases for the 7.5 French. There may be others, but this is where I got my 8x56R cases. You can also find the CCI #34 primers at some gun shows. If you don't reload, I cannot tell you about the commercial offerings.
The best thing to do is clean the bolt and make sure there is no grease in the firing pin hole. only a trace of light oil on the firing pin.
Before trying new ammo try the following using French military ammo then run the same test with new ammo and compare the physical results:
To test French miltary ammo and new ammo point the gun down range, put the safety on and place only one round of ammo in the magazine and let the bolt release (allow to return to battery) and fly home. If the gun does not slam fire carefully extract the round and look at the primer for indentations. A very tiny one can be normal, but more than that can cause the round to go off. Other semis will do this including FN49s and SKS.
If you eventually load more than one round in the magazine and it goes auto say Hi "Bubba"
. BTW I did have this happen with an 8mm FN49-w/Winchester primers and two rounds in the mag. Totally unnerving for a few minutes.Hope this helps
!! Research can truly be frustrating. It seems like every answered question begets five more. 
Thanks all!
