Folks,
I have a letter from P. O. Ackley that states that the 99 Savage is one of the safest action types to be behind as far as being safe from an overload were gas is released into the rear of the action. Safer than any bolt action from his viewpoint.
The 99 design is excellent, likely the best of the lever actions, but with an extreme overload any action type can be unsafe. I have reloaded for close to 50 years and have yet to blow a primer, and I have used dozens of different powders. IMR, Hogdon, Norma, Hercules, Vihtavuori, Winchester.
The point has been well made to start with the minimum load in a good loading manual and work up a grain at a time to be safe, powder like everything else varies a little from batch to batch, though hopefully not enough to damage an action with maximum loads, the worse thing that generally happens is a loose blown primer.
I try to load as close as possible to a full case load of powder by selecting the powder type that works well with full denisity loads, In some chamberings this means H380 works, other require H450 or IMR4350, if you can't get an accurate load with one of these three powders in most chamberings than something is wrong with the firearm. I also use the Norma Powders, especially N203 and N204.
If someone was hurt with a Savage 99 action load, it was not the fault of the Action or it's design, it was a grossly excessive overload that would have destroyed most any action type. And I have seen Model 70 Winchesters and 700 Remingtons and 788 Remingtons blown up. In the case of the 788 Remington the load was so excessive that it stripped the bolt lugs off of the bolt and sent it back into the shooters face. This was in the 1980's just before the 788 was discontinued by Remington.
The Savage 99 is a rear locking action and should give high pressure signs earlier than a front locking action due to the compression of the locking breech block and or stretching of the receiver. You should see high pressure signs early enough to avoid any major event is the point with the 99 action, if you go up a grain at a time with the proper powder being used.