Observe:
The environment- Cold, snow.
The failure- excess pressure within or failure of bolt carrier to contain pressure.
The gas rings- distorted and expanded out of slot.
The position of bolt cam- rotated just under gas tube.
The gas tube- no distortion indicating primary effects of overpressure, possible slight bending caused by secondary effects.
IF this is not the result of a bad handload such as excess loading or wrong powder, some possible causes might be:
The cold- causing lubricant failure to slow movement of bolt and excess pressure to build within bolt carrier.
The cold- causing depressed primer ignition and allowing unburned powder to pass through gas tube into bolt carrier, possibly accumulating and/or ignited by a subsequent firing.
The snow- inadvertant contact with muzzle causing obtruction to barrel and excess back pressure into gas system.
Notice that the bolt is rotated nearly out of battery. This could be because of firng before fully in battery but more likely the bolt was not prevented from rotating because of normal chamber pressure, or excess chamber pressure was not enough to jam bolt against barrel engagement. The bolt carrier began its normal rearward movement, rotating bolt to its present position, almost disengaged from barrel. As pressure built, bolt carrier failed and expanded. The expansion was sufficient to disengage carrier from bolt cam before bolt rotated sufficiently to disengage barrel. The bolt stopped rotating and remained engaged,and chamber pressure did not escape into reciever. All of the observed effects of over pressure are either from excess pressure through gas system into bolt carrier, or a secondary detonation within the bolt carrier, or failure of bolt carrier to contain normal pressure.
Alternativley, excess chamber pressure could cause bolt to jam rearward, increasing friction of rotation slowing rearward movement of bolt carrier and causing excess pressure to build in bolt carrier.