Another cause, though somewhat unlikely, could be the system is grossly over gassed, and/or have an improperly cut chamber.
If the barrel is a carbine length gas port location with a particularly large gas port size (something like 0.075"+), especially if that barrel is 14"+ long, primary extraction may begin while the case is still holding residual pressure. This can result in case head separation.
This is usually seen in rifles who's bolts have the black O-ring in the extractor assembly specified by NSW Crane, as it makes it very difficult or impossible for the extractor to jump the case rim.
This problem arises more with cheaper rifles & barrels. Usually the cause is a concert of errors. Oversized gas port resulting in increased gas flow. Short "commercial" spec (0.4636") headspace combined with a short barrel lead resulting in the projectile sticking in the rifling increases chamber pressure initially. Usually these rifles also have a standard carbine or maybe a H1 buffer which doesn't help matters much.
Basically the most likely culprit is a combination of several out of spec parts leading to a dirty and tight chamber, higher than average chamber pressure, higher bolt velocity, and case head separation. I could go into more detail on at of these points individually, but this is already a long post.
I do not believe the admittedly poor shooting technique to be at fault.
If the barrel is a carbine length gas port location with a particularly large gas port size (something like 0.075"+), especially if that barrel is 14"+ long, primary extraction may begin while the case is still holding residual pressure. This can result in case head separation.
This is usually seen in rifles who's bolts have the black O-ring in the extractor assembly specified by NSW Crane, as it makes it very difficult or impossible for the extractor to jump the case rim.
This problem arises more with cheaper rifles & barrels. Usually the cause is a concert of errors. Oversized gas port resulting in increased gas flow. Short "commercial" spec (0.4636") headspace combined with a short barrel lead resulting in the projectile sticking in the rifling increases chamber pressure initially. Usually these rifles also have a standard carbine or maybe a H1 buffer which doesn't help matters much.
Basically the most likely culprit is a combination of several out of spec parts leading to a dirty and tight chamber, higher than average chamber pressure, higher bolt velocity, and case head separation. I could go into more detail on at of these points individually, but this is already a long post.
I do not believe the admittedly poor shooting technique to be at fault.