Hey guys your right about slow powders and over pressures with mild or light loads.
Do you guys remember when savage came out wth there smokeless muzzle loaders???
Well I got two of the original or ML1 which used a module to hold the 209 primer used for ignition, I knew savages PR guy at the time and I heard thru the grape vine they were going to release them and upon qestioning him he said want to work to test loads??
I was more than happy too.
Well we who were in on the beginning did about 5 years worth of R&D on different powders and there loading screen and even did pressure reads on loads.
We found some very interesting things happen, as I tell you our findings you will understand where a very reputable bullet, brass, and ammo manufacturer developed, or should I say bought the rights to a type of loading screen that give much higher velocities over standardized loads without high pressures and heat.
  Well we first started using fast powders: 5744, 4759, lil gun, 4227 in .50 cal. Gun. 4227 was listed last because it was always hard to ignite and gave poor accuracy in most guns 
  Now guys started to thinking what about slower powders ?
Well we started to look at loads for cartridge guns and trying them
Imr4198 and h4198 were tried but they were very erratic with accuracy. Loads for these were 300 grain hornady XTP's with sabot
And a favorite load of 5744 was 40-45 grains by weight. This was very accurate and recoil was light but this was the limit load wise for the faster powders but it did exactly what the inventor of this system wanted - a light recoiling muzzleloader with good killing power for his wife,nlittle did he know he had opened pandora station box!!
Well we started to look closer at what was happening??
I don't remember who did this first but they took a weighted amount of fine sugar and poured it in and then there then seated a saboteur bulle, 300 gr. XTP.  Then loaded up a 209 primer and fired it. It moved 1-1/2" to 2-1/2" up the bore !