Let's look at that a little more closely
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smokeless powders do in fact burn much slower than BP. Smokeless is produced in various compounds by all the makers with a broad range of burn speeds. Even the faster burning such as 231 burn slower than BP. The key to smokeless efficiency is in fact the slower burn rate. Peak pressure of smokeless is delayed by its slower burn rate . BP burn rate is much quicker. The pressure curve is near instant. However, it is not an efficient propellant. That's what allows us to use such a broad range of BP loads in our guns. Smokeless on the other hand has a much higher efficiency but due to its slower burn rate it doesn't release its gasses as quickly. However, the burn rate of smokeless increases as pressure increases. That's why one must carefully scale smokeless and not go beyond established limits. It doesn't take much over those limits to result in destruction of the gun.
I don't know who has done that testing but I'd like to have seen it.....from a distance.
Yeah, I was thinking that exact same thing