ORIGINAL: driftrider
The recommended load for XMP-5744 is 44 grains. Bridges had shot and undisclosed number of shots at 48 grains (9.1% over max by weight) before firing the 49 grain load (11.4% over max by weight) that blew the gun up.
With smokeless powders, burn rates and pressure levels depend on both the amount of powder, the design of the powder (powder specific burn rate) and also the pressure it's burned at. When pressure levels in a smokeless firearm reach a certain level the burn rate and pressure levels can spike erratically. That's why load manuals for smokeless arms have MAX loads that should NEVER be exceeded under any circumstances by a reloader who lacks a fully equipped ballistics lab with pressure test equipment. The Savage is no different.
I looked up the load data on the Savage site. The chart gives a weight range of 41-44 grains for the XMP-5744 powder. However, these are referred to as recommended loads and no where is there any mention of a maximum recommended load for it or any of the other powders listed. You could assume the 44 grains is the maximum recomended load, since it is the highest figure listed, but Savage confuses things somewhat by adding a statement that says one should try 1 or 2 grains more, or less, for a particular load. With this in mind, the maximum load listed would be 46 grains, but wouldn't it be clearer, and safer, for Savage to plainly and clearly state a maximum recommended load.
If you read the whole article, you find that one of the other failures was caused by a powder that is not on Savage's load recommendations, yet it was stated that the load was recommended by a Savage engineer. Of course we can't know for sure if it actually was. However, the article does point out another statement in Savage's load recommendations which states that the rifle is "designed, engineered and built to handle the higher pressures of modern smokeless propellants such as those listed". This is somewhat ambiguous and I think Savage should be much clearer on acceptable powders and maximum recommended loads for each.
The thing that really concerns me is that there appears to be a perception among some Savage users that it is virtually impossible to overload the rifle to create a dangerous pressure situation, when using plastic sabots, because the sabots will fail from the high pressure and act as a safety release, therefore avoiding any dangerous pressures in the barrel. I have read this several times, from different persons. Toby was specifically testing for sabot failure and the 48 grain load apparently showed no signs of extreme pressure on the spent primer or recovered sabot, yet the first attempt with the 49 grain load blew up the barrel. With the other pressure related failures, it certainly appears that the sabot will not fail before creating a dangerous situation. There are also stories all over the internet about how Savage purposely abused their rifles, with extreme loads, and could cause no damage. Such stories only add to the dangerous perceptions of some and increase the possibility of an accident.
Lastly, some, including representatives of muzzleloader manufactures other than Savage, have stated that using smokeless powder in a muzzleloader, even one designed for it, is a set up for some serious accidents. Many passed this off as sour grapes statements, but I believe it is fair to say that there is much less room for loading error, with smokeless powders, than with blackpowder or substitutes. Since Savage can not control the loading procedures of all those who buy and use their rifles, these statements do have some validity. Therefore, I believe it is paramount that Savage starts to do a better job of safety education, including much more specific load recommendations and actively countering any public misconceptions .