I think DocGKR had a good response to the 357 Sig round in the 4th page of the thread " Observations from actual shooting". His response as Follows:
patscrazy--I am curious why you would think .357 Sig penetrates common cover better than other calibers; didn't your agency conduct testing or at least review the results from other agencies, such as the FBI BRF, prior to selecting you new caliber?
While .357 Sig is a very reliably performing 9mm bullet, it is does not offer significantly better terminal performance compared with the best current 9mm ammunition. When firing through heavy clothing, automotive steel panels, automobile windshield glass, interior wall segments, exterior wall segments, and plywood, both the 357 Sig Speer 125 gr JHP Gold Dot and 9mm Speer 124 gr +P JHP Gold Dot exhibited nearly identical penetration and expansion results THROUGH ALL THE DIFFERENT BARRIERS, as demonstrated by both our testing and that of the FBI BRF. Most 357 Sig loadings, unless they fail to expand, do not offer excessive penetration; in fact, the exact opposite, under-penetration, can be a problem. Several .40 S&W and .45 ACP loads offered superior terminal performance through barriers compared to the 9mm and 357 Sig loads. In addition to having tested virtually all the handgun ammo available in lab settings, we have also had the opportunity to analyze numerous OIS incident forensic results and have not observed any greater incapacitation in actual shootings with users of 357 Sig loads compared to those users of 9 mm, .40 S&W, or .45 ACP who are using equivalent modern, well engineered ammunition.
The 357 Sig is not a bad cartridge, it just does not seem to offer anything that is not already available, at the price of less ammunition capacity than the similarly performing 9mm, as well as having greater recoil, muzzle flash, and wear on the weapon compared to other service pistol cartridges. On the other hand, since the 357 Sig is a modern cartridge benefiting from the latest engineering concepts, the bullets loaded with it have generally all been designed and tested using the latest FBI, IWBA, etc... testing protocols. This results in more robust terminal performance, less failures to expand, and thus greater tissue damage than will be found with older projectile designs. In addition, since according to data from Fackler and others, approximately 50% of shooting victims are incapacitated by psychological mechanisms, it is possible that the increased blast, flash, and noise of the 357 Sig enhances psychological perceptions of being shot.
In discussing this issue with an experienced ammunition engineer at one of the major ammo companies, he stated that he didn't particularly like the 357 Sig from an engineering perspective and described their difficulties in designing and producing 357 Sig ammunition which consistently performs as well as their ammunition in other service calibers. In particular, he felt his company's 357 Sig loads offered no better performance than their top 9 mm loads and stated their .40 S&W loads were superior in every respect to their 357 Sig ammunition. He firmly believes their .40 S&W offerings are the best performing duty ammunition his company produces.
Contemplate this--Prior to transitioning to .40 S&W, the CHP used a variety of .357 Mag loads, depending upon what was available via the state contract. According to the published CHP test data, the .357 Magnum load used immediately prior to the CHP transition to .40 S&W was the Remington 125 gr JHP with an ave. MV of 1450 f/s from their duty revolvers. Yet despite the decrease in velocity, the CHP has continued to report greater success in OIS incidents (both better terminal performance, as well as intermediate barrier ability) with their .40 S&W 180 gr JHP than with the .357 Magnum 125 gr JHP they previously issued.
Lets compare apples to applesbelow is factory test data from various Winchester LE loads in different calibers, Ranger-T as well as Ranger Bonded. How does the .357 Sig compare to the other service calibers with respect to intermediate barrier penetration?
FBI Test Protocols:
Bare Gelatin at 10ft
Denim, 4 Layers at 10ft
Heavy Clothing at 10ft
Steel, 2 pieces of 20 gauge at 10ft
Wallboard, 2 pieces of 1/2" gypsum board at 10ft
Plywood, 1 piece of 3/4" AA fir plywood at 10ft
Automobile Glass, 1 piece 1/4" laminated safety glass set at a 45 degree angle with an offset of 15 degrees at 10ft
9mm 127gr +P+ RA9TA at 1250fps:
Bare Gel: 12.3/.64
Denim: 12.2/.68
Heavy Cloth: 12.2/.68
Wallboard: 12.1/.66
Plywood: 12/.68
Steel: 20.5/.40
Auto Glass: 9.4/.48
9mm 147gr RA9T at 990fps:
Bare Gel: 13.9/.65
Through Denim: 14.5/.66
Through Heavy Cloth: 14/.66
Through Wallboard: 15/.67
Through Plywood: 14.8/.62
Through Steel: 17/.45
Through Auto Glass: 10.8/.52
357Sig 125gr RA357SIGT at 1350fps:
Bare Gel: 10.9/.63
Denim: 12.1/.66
Heavy Cloth: 10.7/.69
Wallboard: 15.4/.48
Plywood: 12.2/.66
Steel: 23.4/.41
Auto Glass: 10.3/.49
.40S&W 180gr RA40T at 990fps:
Bare Gel: 13.8/.60
Denim: 14.3/.70
Heavy Cloth: 13.4/.64
Wallboard: 13.1/.66
Plywood: 15.1/.64
Steel: 17/.52
Auto Glass: 12/.61
.45ACP 230gr +P RA45TP at 990fps:
Bare Gel: 13.2/.79
Denim: 15.2/.78
Heavy Cloth: 15.7/.78
Wallboard: 13.8/.75
Plywood: 14.6/.77
Steel: 20.6/.53
Auto Glass: 13.6/.60
How about bonded bullets?
9mm 124gr +P at 1180 fps:
Bare Gel: 12.6/.68
Denim: 18.7/.54
Heavy Cloth: 18.2/.56
Wallboard: 11.9/.64
Plywood: 15.8/.57
Steel: 22/.42
Auto Glass: 12.7/.58
9mm 147gr at 995fps:
Bare Gel: 14.7/.62
Denim: 16.5/.59
Heavy Cloth: 15.8/.58
Wallboard: 16.7/.56
Plywood: 16.5/.59
Steel: 19/.42
Auto Glass: 12.6/.55
357Sig 125gr RA357SB at 1350fps:
Bare Gel: 12.5/.59
Denim: 15.9/.57
Heavy Cloth: 16.9/.55
Wallboard: 14.7/.62
Plywood: 16.0/.60
Steel: 21.7/.44
Auto Glass: 12.8/.62
.40S&W 180gr at 1070fps:
Bare Gel: 14.8/.67
Denim: 21.8/.51
Heavy Cloth: 19/.59
Wallboard: 16.7/.61
Plywood: 15.5/.62
Steel: 14.8/.55
Auto Glass: 12.4/.63
.45ACP 230gr RA45B at 905fps:
Bare Gel: 14/.73
Denim: 15.8/.67
Heavy Cloth: 15.8/.68
Wallboard: 14.7/.69
Plywood: 16.5/.74
Steel: 14.8/.56
Auto Glass: 12.5/.66
As can be seen above, basically all the standard service calibers work when using good quality ammunition. The platform picked tends to dictate the caliber.
Don't over-think this subject; projectiles, particularly handgun bullets, simply poke holes in things, just like arrows, spears, daggers, or shivs. The only difference is that bullets allow you to poke the holes from further away... Since shot placement is the key with handguns, if given the choice, I'd much rather be defended by a guy who practices with 500 rounds per month of 9mm, than one who caries a .357 Sig, but only shoots 500 rounds per year.
As always, the most important things to focus on are:
-- Cultivate a warrior mindset
-- Invest in competent, thorough initial training and then maintain skills with regular ongoing practice
-- Acquire a reliable and durable weapon system
-- Purchase a consistent, robust performing duty/self-defense load in sufficient quantities (at least 1000 rounds) then STOP worrying about the nuances of handgun ammunition terminal performance.