Here we go. From Berger's website.
Limitations to the Bullet's Structural Integrity
Another thing that happened when we released these bullets to the public is that they were fired in cartridges that are more energetic than the .338 Edge which I used for the initial evaluations. Upon exposure to the extreme pressures and accelerations produced by some of the larger cartridges, some negative results were observed; poor groups, and lower observed BC (even lower than the revised values above). Our current working theory is that the poor precision and reduced BC are a result of nose slump. Nose slump is when the bullet is accelerated so fast that the base of the nose can't support its own weight, and bulges out to fill the barrel. This produces a bullet with a longer bearing surface and a shorter nose which explains the compromised BC. Since this deformation doesn't occur exactly the same every time, poor precision also results.
The exact threshold of pressure/acceleration that will cause nose slump with this bullet is not known. There are a number of small to medium capacity cartridges that shoot these bullets very well, with extremely good precision and a repeatable BC. So far there have been no reported cases of nose slump with cartridges in the following class: .338 Winchester Mag, .338 Norma Mag, .338 RUM, and .338 Edge, etc.
The .338 Lapua Mag seems to be a borderline case which may or may not produce nose slump. Factors that affect pressure/acceleration will affect the likeliness of nose slump occurring. For example, ball powders are typically faster burning than stick powders, so they produce higher peak pressures, and are more likely to produce nose slump. Tighter bores can also cause elevated pressures and tip the scales toward nose slump.
Cartridges like the .338 Lapua Mag Improved and larger are virtually assured of producing nose slump when loaded to their potential pressures.
If you're working up a load with these bullets and having difficulty finding a precise load, it's likely that you're exceeding the pressure threshold where nose slump happens. In small to medium cartridges, the hybrid ogive design makes it quite easy to find an accurate load. The bullet is quite insensitive to seating depth. If you're working with a large capacity case and having poor results, you should consider reducing the powder charge until good groups are achieved.
When designing a bullet for use in hunting applications, the toughness of the bullet is always a trade-off. Terminally, you want a bullet that is capable of reliable expansion/fragmentation at low impact velocities. However, the bullet can't be so thin-skinned that it doesn't survive being launched at very high speeds. This being our first time working with a bullet this large, a construction was selected which we felt would strike the best balance between toughness and terminal performance. Simply put, we erred too much on the side of terminal performance. The result is a bullet that's perfectly suited for small to medium capacity cases, but simply isn't tough enough to survive being fired from the more energetic magnums.
The good news is that the situation has been identified and several solutions are already being worked on. We know the design needs to be 'toughened up' for successful use in larger cartridges, and we're considering the best way to do this.
