09-24-2022, 11:13 PM
The Lapua hate in this thread belies the lack of information of why it happened. It could be that the tolerances of the action parts are such that an OOB situation is possible in this rifle, regardless of the brass manufacturer.
The only thing we can say for certain is related to proof of the null hypothesis. If the hypothesis is that Lapua is flawed then the null hypothesis is that Lapua does not fail in all situations. What percentage of failures we are willing to accept is up to the shooter.
Any QL hate also belies how it is a extremely useful computer prediction for the average shooter. For example, how else would we know that the OP's load is 106% compressed at his stated OAL? Crunching powder changes burn characteristics and introduces the unknown, always more pressure, and in this case may be the reason deflagration turned into detonation. Regardless, it is a computer program which is only as good as inputs: GIGO. The 106% prediction is based on the default case volume, which could be more or less based on reality. If the OP weighed the water capacity it would be a better pressure prediction. QL default is 35.99gns of water. My unfired Lapua is 35.13gns (less capacity than default), so predicts 108.4% compressed and higher than default pressure of 67.5K lbs peak pressure. While I accept QL is not exact this is a hot load in any conservative discussion.
From Bill Alexander on Sniper's Hide which 52 was also part of the discussion (March 22, 2022);
[INDENT]The Grendel chamber geometry and bolt was designed in concert with the Lapua case. The chamber "if" correctly dimensioned and with the correct feed cone geometry will allow chamber pressures well in excess of 68k psi without the case deforming. Obviously this is for Proof loadings only and should NOT be used as the basis of any load development. It will damage the rifle! The absolute maximum is 51,800 psi and MAOP pressures are held around 50k psi. Pushing loads to 52kpsi allows zero envelope for pressure excursions, which will and do happen even with the most carefully assembled loads.
Stretching of the case above the web results from either an incorrectly machined barrel or excess residual bore pressure as the case is extracted. I do not have direct experience of the 6mm ARC but simple expansion ratio calculations indicate the timing will need attention. This is not just the size and position of the gas port in the barrel but also the reciprocating mass which includes the impulse from the fire control group.[/INDENT]
If anyone wants to get rid of their unsafe Lapua brass, I will safely dispose of them by gradual destruction over 20 firings.
The only thing we can say for certain is related to proof of the null hypothesis. If the hypothesis is that Lapua is flawed then the null hypothesis is that Lapua does not fail in all situations. What percentage of failures we are willing to accept is up to the shooter.
Any QL hate also belies how it is a extremely useful computer prediction for the average shooter. For example, how else would we know that the OP's load is 106% compressed at his stated OAL? Crunching powder changes burn characteristics and introduces the unknown, always more pressure, and in this case may be the reason deflagration turned into detonation. Regardless, it is a computer program which is only as good as inputs: GIGO. The 106% prediction is based on the default case volume, which could be more or less based on reality. If the OP weighed the water capacity it would be a better pressure prediction. QL default is 35.99gns of water. My unfired Lapua is 35.13gns (less capacity than default), so predicts 108.4% compressed and higher than default pressure of 67.5K lbs peak pressure. While I accept QL is not exact this is a hot load in any conservative discussion.
From Bill Alexander on Sniper's Hide which 52 was also part of the discussion (March 22, 2022);
[INDENT]The Grendel chamber geometry and bolt was designed in concert with the Lapua case. The chamber "if" correctly dimensioned and with the correct feed cone geometry will allow chamber pressures well in excess of 68k psi without the case deforming. Obviously this is for Proof loadings only and should NOT be used as the basis of any load development. It will damage the rifle! The absolute maximum is 51,800 psi and MAOP pressures are held around 50k psi. Pushing loads to 52kpsi allows zero envelope for pressure excursions, which will and do happen even with the most carefully assembled loads.
Stretching of the case above the web results from either an incorrectly machined barrel or excess residual bore pressure as the case is extracted. I do not have direct experience of the 6mm ARC but simple expansion ratio calculations indicate the timing will need attention. This is not just the size and position of the gas port in the barrel but also the reciprocating mass which includes the impulse from the fire control group.[/INDENT]
If anyone wants to get rid of their unsafe Lapua brass, I will safely dispose of them by gradual destruction over 20 firings.