Yes it can be a headspace issue. Were the cases fired in this rifle before you loaded them? If fired in a rifle with tighter headspace they would not fit snug in your chamber. Any cases fired with light loads should be set aside and not used for full power loads as they can develop excessive headspace. The firing pin can drive the case forward, the primer will detonate and back out to the bolt face. If there is insufficient pressure to overcome case wall friction in the chamber and push the case back, it will develop excessive headspace.
I never mix cases. This may be overkill to some, but I keep my cases segregated by rifle and only fire them in that particular rifle. I load rifles for accuracy and dependability, not volume of rounds.