11-23-2021, 11:55 PM
BC,
The important thing is you are OK. It's not pleasant to have that happen.
I have seen this in Blackout in a Remington bolt gun. The guy was shooting about three benches from me and loading at the range. He loaded a heavy bullet (subsonic) on top of a charge meant for a light bullet (supersonic). So a 220gn bullet when the charge was meant for a 110 or 115 bullet. A bigger than normal boom. Smoke all around him and people looking at him. The bolt was sticky and the base of the case split away and looked exactly like yours. It was hammered into the bolt face so tight he never got it out. Maybe he could have been more gentle but I saw big gouge marks in the bolt face where he had used tools and an order for a new bolt.
Yours looks similar but less pressure perhaps if that case base was not welded into the bolt face and came out of the bolt face without too much fuss.
That appears to be an overpressure incident at the time of firing. The only place overpressure can go when the bolt is in battery is the thin unsupported void between the front of the bolt lugs and the start of the chamber. Obviously it could simply overwhelm the bolt lugs but they held firm at whatever pressure the case split.
Using the volume of a Lapua case after sizing (35.92gns water) in Quickload your load predicts 58.7K psi and 105.5% compressed. It is over SAAMI but I would not expect such a catastrophic event. Plus, if you have fired the same load previously and it was verging on case splitting then there would have been other indicators; sticky unlocking, flat primers, unusual recoil in the earlier rounds. That sheared case is equivalent to a deliberate overproof test to destruction by a manufacturer.
If you poured powder up to the case mouth and compressed a bullet into it then maybe, but you would have seen and felt this when reloading.
I do not have data for the 120AMax but I do for the 123AMax and the bullet's OAL to touch lands is no different than most others. What I mean is, the spike pressure that happens when a bullet is jammed in the rifling is unlikely to be the case here. Do you have an idea of the throat in that rifle? The headspace might be fine but the throat is tight. Or the case OAL is too long for the chamber's neck and it crimps into the bullet when it goes into battery.
My money is on a bullet that could not move at the time. Neck of the case crimped into the bullet, or a throat/barrel obstruction. Maybe the diameter of the bullet was too wide for the bore (manufacturer error).
How easy was it to get the case base out of the bolt?
Where was the offending bullet hole on the target, and was it a nice round hole (stable bullet)?
What is the brand of bolt - very impressive that no lugs broke? I wonder if the bolt is now weakened.
You could measure the diameter of all the rest of the bullets in that box.
Also, I would check the OAL to know exactly when those bullets touch lands.
If a heavier bullet was loaded into the case accidentally you would know this already - whether you even have them and how close are they to the 120box on the shelf etc.
Again, all good that you're OK but you do need to know what happened to restore faith in the gun and ammo or it will happen again.
.
The important thing is you are OK. It's not pleasant to have that happen.
I have seen this in Blackout in a Remington bolt gun. The guy was shooting about three benches from me and loading at the range. He loaded a heavy bullet (subsonic) on top of a charge meant for a light bullet (supersonic). So a 220gn bullet when the charge was meant for a 110 or 115 bullet. A bigger than normal boom. Smoke all around him and people looking at him. The bolt was sticky and the base of the case split away and looked exactly like yours. It was hammered into the bolt face so tight he never got it out. Maybe he could have been more gentle but I saw big gouge marks in the bolt face where he had used tools and an order for a new bolt.
Yours looks similar but less pressure perhaps if that case base was not welded into the bolt face and came out of the bolt face without too much fuss.
That appears to be an overpressure incident at the time of firing. The only place overpressure can go when the bolt is in battery is the thin unsupported void between the front of the bolt lugs and the start of the chamber. Obviously it could simply overwhelm the bolt lugs but they held firm at whatever pressure the case split.
Using the volume of a Lapua case after sizing (35.92gns water) in Quickload your load predicts 58.7K psi and 105.5% compressed. It is over SAAMI but I would not expect such a catastrophic event. Plus, if you have fired the same load previously and it was verging on case splitting then there would have been other indicators; sticky unlocking, flat primers, unusual recoil in the earlier rounds. That sheared case is equivalent to a deliberate overproof test to destruction by a manufacturer.
If you poured powder up to the case mouth and compressed a bullet into it then maybe, but you would have seen and felt this when reloading.
I do not have data for the 120AMax but I do for the 123AMax and the bullet's OAL to touch lands is no different than most others. What I mean is, the spike pressure that happens when a bullet is jammed in the rifling is unlikely to be the case here. Do you have an idea of the throat in that rifle? The headspace might be fine but the throat is tight. Or the case OAL is too long for the chamber's neck and it crimps into the bullet when it goes into battery.
My money is on a bullet that could not move at the time. Neck of the case crimped into the bullet, or a throat/barrel obstruction. Maybe the diameter of the bullet was too wide for the bore (manufacturer error).
How easy was it to get the case base out of the bolt?
Where was the offending bullet hole on the target, and was it a nice round hole (stable bullet)?
What is the brand of bolt - very impressive that no lugs broke? I wonder if the bolt is now weakened.
You could measure the diameter of all the rest of the bullets in that box.
Also, I would check the OAL to know exactly when those bullets touch lands.
If a heavier bullet was loaded into the case accidentally you would know this already - whether you even have them and how close are they to the 120box on the shelf etc.
Again, all good that you're OK but you do need to know what happened to restore faith in the gun and ammo or it will happen again.
.