I no longer have any of the early info I once collected regarding many of the velocity comparisons.
I think your second statement is about as generally appropriate as anything else that's been offered.
From Winchester's catalog ...
X3576P 125gr .357 Magnum, 4" Vented barrel:
1450fps @ muzzle; 1427fps @ 5yds; 1338fps @ 25yds
583fpe @ muzzle; 497fps @ 25yds
RA357SIGT 125gr 357SIG, 4" barrel:
1350fps @ muzzle; 1331fps @ 5yds; 1262fps @ 25yds
506fpe @ muzzle; 442fpe @ 25yds
These are the same figures listed for both the Q4309 (125gr FMJFN) & the USA357SJHP (125gr JHP)
A couple of things have always stood out, at least to me, since I first started reading all of the articles, reviews, ballistics tests, etc. for the 357SIG ... and especially after shooting the cartridge.
Many magazine article authors have always said that the solid barrel of the semiauto pistol provides the advantage of lacking the barrel/cylinder gap of a revolver ... and it does ... but they've often also claimed that this is why the semiauto caliber can achieve the performance of the rimmed revolver cartridge.
That being the case, why did earlier ballistics testing of service length 4" revolvers often show a velocity of 1400-1450fps for 125gr .357 Magnum ammunition, and yet the average major ammunition manufacturers ... such as Winchester, for example ... often show a tested velocity of only 1350fps from 4" barrels in the 357SIG?
Sure, the unburned powder (responsible for the greater muzzle flash in 4" barreled service revolvers) in the revolver cases DID provide for even higher velocities in longer revolver barrels, and some of the revolver round's potential was unrealized in 4" barreled revolvers.
But why is the average major factory ammunition only generating in the low-to-mid 1300's fps with the 125gr 357SIG load from solid semiauto barrels?
I guess what the magazine writers really meant was that the new 357SIG was able to attain the "lesser" potential .357 Magnum velocities realized out of short service length revolver barrels ... which is what a couple of authors actually implied, if not directly said.
So, the 357SIG does almost reach the velocities of the .357 Magnum, but only in the Magnum's lesser performance envelope, when fired out of shorter revolver barrels.
Since this was the common service length barrel, and the barrel length involved in most of the earlier anecdotal "street performance" statistics, it makes sense that it would be appropriate to "compare" the new semiauto pistol caliber to it. It DID have many magazine authors' approval as being the defensive hangun caliber "King of the Street", as one author called it ...
Actually, I used to have some older chrono listings for some 125gr .357 magnum loads fired out of 2.5" & 3" revolvers ... and the velocities listed showed a broad average in the low-to-mid 1300's fps ... just about where a 4" 357SIG pistol seems to exhibit velocities with 125gr loads.
Of course, many of the smaller ammunition companies are offering faster velocities in 357SIG, although most of them are using bullets that have been designed and tested for slightly lesser optimal velocities. That doesn't mean they may not perform well at the highter velocities ... but neither does loading them to faster velocities necessarily guarantee "better" performance. That's what standardized, carefully controlled testing can determine for us ...
So, the fans of the 357SIG will naturally say that none of this matters, because the cartridge is better when it comes to perceived recoil & controllability ... but that might be more the result of the platform in which it's being used.
It also can be carried in greater capacity magazines. True.
Then, there's the bullet design issue. Revolvers aren't sensitive to "feeding" issues ... and the revolver caliber does offer a lot more versatility in regard to bullet weight & design.
But it still seems to me, anyway, to always come back to the how the 357SIG is kinda, sorta, supposed to duplicate the performance of the more powerful revolver round's "statistical street results" ... when the revolver round was fired from the shorter service length barrels.
As I remember when I used to carry an issued .357 Magnum revolver, it was explained to me that we issued the shorter 4" barreled models ... instead of the longer, and potentially more powerful 5"-6" barreled models ... because it was more comfortable for the smaller statured cops that started entering L/E in the 70's. Nobody really wanted to argue that the longer barrels might not offer a bit more "performance" than the shorter barrels, though ... It was more that the shorter barrels seemed to offer "enough".
Of course, it didn't hurt that the M19 was reportedly Bill Jordan's favorite balance of platform size, weight and caliber performance ... but he was probably a bit "better" when it came his presentation and shooting skills than most folks wearing badges hither & yon ...
I've always wondered what Bill Jordan might've said if someone told him he HAD to carry a Level 3 security holster, instead of his "antiquated", unsafe ... from a modern "officer safety viewpoint" ... preferred pouch holster.
So, I think the 357SIG probably WAS intended, at least partially, to duplicate the "popular" American .357 Magnum 125gr load ...
Did it achieve its goal?
Well, if you consider the average velocities of the major American ammunition manufacturers ... probably not quite ... not at velocities in the 1300's fps.
Is it "performing" well? Well, the anecdotal results seem to indicate it's working as well as the other 3 major calibers in use in L/E ... and that's an entirely different, and muchly debated, topic.
Just to leave you with this final thought ... a recap of the earlier Winchester data, with the RA9TA 127gr +P+ 9mm load listed ...
125gr .357 Magnum - 1450fps
125gr 357SIG - 1350fps
127gr 9mm +P+ - 1250fps
So, I suppose velocity-wise the 357SIG is about halfway between the 9mm +P+ (and a couple of other 124gr +P loads, which are more easily available to non-L/E) and the .357 Magnum ... but only when fired from a short barreled revolver.
I've always LIKED the .357 magnum cartridge, but then I spent a lot of range time toward developing my skills with it. I carry the 9mm in the hotter major factory loadings because I feel it's adequate for my defensive needs ... and it's also issued to me ... but the 357SIG leaves me a bit lukewarm.