Bugger,
The only problems I've seen with Sierras have been when they were driven too fast and then used at short range.
Most cup-and-cores or any type work best when driven no faster than about 2800 fps at the muzzle, and 2700 with a heavier bullet is usually better, because the bullet will retain more velocity at longer ranges so still expand, yet not have as much tendency to come apart up close. Have shot many animals with the 160 Sierra GameKing from the 7x57 at around 2650-2700 and never had a problem from 100 yards to almost 400.
Have seen the 130 Sierra .270 GameKing come apart a few times when driven at 3000 fps or more on closer game, though it usually works fine from 200 yards out. In general, if I want 3000 fps out of a cup-and-core and might shoot something under 150-200 yards, the Hornady Interlock is the choice.
When I used the 105 Speer Hot-Cor in the .243 the muzzle velocity was around 2800 fps, and only one bullet came apart--but the core still penetrated and killed the deer. When I used the 140 Speer Hot-Cor in the .264 Winchester the muzzle velocity was around 3200, but I only used it for deer in open country, minimum range about 200 yards, and the result was always a wound channel and exit of about 1".
Have only seen one softpoint cup-and-core not expand (or at least not expand much), a 120-grain Nosler Solid Base from a .257 Roberts at about 2850 fps. Shot a big mule deer buck in the lungs broadside, just behind the shoulder, and he went 200 yards before falling. The hole through the lungs was very small, as was the exit. In fact only found one tiny drop of blood, right where he was shot.
But anything is possible, and you never know when some bullet company tweaks the design, or somebody on the assembly uses the wrong lead alloy for the cores, or does something else to screw up some bullets. But those are the exceptions and not the rule.
