Quote:
Originally posted by Billy Shears
Joshua,
I'm no expert on these things, but I "think" there are two main "ingredients" in muzzle blast:
1. When the bullet breaks the sound barrier...roughly 1150 fps at sea level; and
2. When unburned/still burning powder is still rapidly expanding as it leaves the muzzle.
This is why in my previous post I suggested slower bullets and faster powder.
I believe it is mainly this second reason that gives the .357 its notorious ear-splitting blast and is easily replicated when handloading. A load of H-110 is FAR louder than a load of Unique.
9mm cartridges are typically loaded with faster burning powders than factory .357s. Therefore, even though the bullets are theoretically moving at the same velocity, and should have similar levels of sonic boom, the revolver round is still "exploding" as it leaves the muzzle. That's the source of your sinus clearing blast.
I'm sure this explanation is both incomplete and partially incorrect, so hopefully others with far more knowledge will be along shortly.
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This is, I believe, pretty much correct. It's not so much the velocity of the bullet as it is the amount of burning powder and gas coming out of the barrel. Think about it for a minute: a gun with a short barrel is almost always louder than a gun of the same caliber firing the same ammunition from a longer barrel. If the velocity of the bullet were directly related to the loudness of the report, the situation would be inverse since the guns with shorter barrels usually produce lower velocities than guns with longer barrels.
The difference between a 158gr .357 Magnum and a 124gr 9mm +P is that, even though they produce roughly the same velocity, the .357 Magnum is burning a lot more powder to get there. For example, my standard "full power" .357 Magnum handload consists of a 158gr LSWC bullet over 14 gr of Alliant 2400. While certainly not a starting load, it is still well below current book maximums though I hold it a bit lower since I'm using Winchester primers. That being said, I rarely see 124 gr 9mm loading data with any powder/primer combination using a maximum load of over 8-9 gr and some of the faster powders are even a good bit less.
The reason that I think the full-power 125gr .357 Magnums are so ear splitting is not because of their higher velocity, but because they use even larger charges of powder than the 158 gr loadings do. For example, the book maximum powder charge for a 158 gr .357 using 2400 is less than the starting load for a 125 gr .357 using the same powder. While I've never pulled them apart myself, people who've been ambitious enough to do so have reported that full-power factory 125 gr .357 Mag loadings often contain powder charges similar to maximum or near maximum book loads of slow powders like H110 or Winchester 296. Per Hodgdon's website, the max load for both of these powders is
22 gr. By comparison, the heaviest maximum charge they list for any 124 gr 9mm loading is only
6.6 gr of HS-6, so the .357 Magnum is burning over three times as much powder.