In a sufficiently short case, it is possible that initial penetration of pyrotechnic plume can reach far enough into propellant charge so that essentially the entire charge is contained within the primary ignition volume. It is also possible that in a relatively large case, charged with a sufficiently small volume of a sufficiently easily ignited propellant, primer plume can ignite essentially the entire charge but see the following paragraph.
Readers should note that any smokeless propellant could become sufficiently brittle under arctic conditions as to make firing the gun patently unsafe. Several years ago, our esteemed Editor forwarded a letter to this author from an Alaskan shooter who was experiencing unusually high pressures with his 300 Winchester Magnum load using a charge of 4350 that should have produced perfectly normal pressures – as I recall, the correspondent had to hammer the bolt open. He was testing in the dead of winter at temperatures near minus 40-degrees. I wrote him a long explanatory letter and begged him to cease and desist such testing – since I have not heard back, I have to wonder if my letter arrived in time! Shooting in temperatures below about minus 40-degrees is particularly dangerous, in this regard, and also because the steel of the gun becomes progressively more brittle as temperature drops – a classic double-edged sward.