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The All New 357 SIG CartridgeIt's Not A Necked Down .40!

Written By: Marv Stenhammar

Written September 1998 - Updated on 6 February 2000

For several months, and now years, I have been hearing and reading that the .357 SIG case is made from a necked down .40 S&W case. Several prominent gun magazines have reprinted this misinformation, adding to the confusion. The original .357 SIG article released in Handguns (Feb '96) was correct in stating that the 357 SIG is an all new round, and, though similar, it is NOT a necked down .40!

Fact:  The .357 SIG is NOT a necked down .40.  

Fact:  If you use .40 S&W brass to make .357 SIG Ammo, you will most likely damage your gun or yourself.  You may be unlucky and hurt an innocent bystander.

Fact: While the .40 S&W & .357 SIG case head diameter, extractor groove, and primer pocket are by design identical,  the overall length, headspacing, and interior wall profile are completely different. 

To get the facts, I went to a contact at SIG Arms in Exeter, N.H., and asked the question: Is the .357 SIG a necked down .40?  Here is the answer I received from a SIG engineer:

"No, they are not the same case. The .357 SIG is not a necked down .40. As you know, the folks here at SIG were looking to duplicate the .357 Magnum terminal ballistics (1350 fps at over 500 ft/lbs.) in an auto loader. In fact, SIG and Federal leaned heavily on the .30 Luger and the .30 Mauser cartridges of the early 1900's.  Having made several guns in .40 S&W first, this helped them get into the police market and made it simple for the modification to .357 SIG."

More Facts:

I also called, then later met with, an engineer from Federal at the 1999 SHOT Show. Here is some of the info they shared with me.

- The .357 SIG has a maximum average pressure of 40,000 psi, compared to 35,000 psi of the .40 S&W case.  The lower wall of the .357 SIG case is thicker and stronger to handle these higher pressures.  The .40 S&W case will split and come apart if they are "necked down" and loaded to 40k psi.

- The .357 SIG case is somewhat similar to the .40 S&W, but is highly modified. The .357 SIG is bottlenecked, and is slightly longer (.015) than the .40. The lower wall of the .357 SIG is also thicker and stronger to handle higher pressures. The bottleneck causes the pressure and the velocity to be much greater by design, and the thicker case wall in the .357 SIG cases allow for this higher pressure.

- The .40 S&W cartridge length is .850"; the .357 SIG is .865". While the case head diameter, extractor groove, and primer pocket are identical between the .357 SIG and .40 S&W, the overall length, headspacing, and interior wall profile are different.

- The .357 SIG does headspace at the case mouth. Federal said that headspace is easier to control if it is based on overall length rather than midway up the shoulder. However, they added that the headspace of the shoulder must be proper as well. So in fact there are two headspace measurements, the OAL and shoulder headspace.  For experienced, or even new, reloaders this should be no big deal as there are several bottlenecked cartridges out there that require attention be paid to both the OAL and shoulder measurements.

Strategy:  SIG and Federal used the diameter, extractor groove, and primer sizes of the .40 S&W to facilitate the easy "drop in" of .357 SIG replacement barrels in both newer and older guns.  The only modification needed to run .357 SIG in a .40-designed gun is a new .357 SIG barrel.   This designed interoperability allowed SIG and Federal to quickly gain market share in the already established .40 S&W law enforcement (LE) and concealed-carry (CCW) gun market.  It also means that after the .357 SIG design was fleshed out, they only had to drop in the barrels to convert their existing inventory to .357 SIG.  Since several other manufacturers now offer several guns in .357 SIG chambering, the design strategy worked.

Since I originally published this back in September of '98, I have reloaded several thousand rounds for the .357 SIG. Here are a few observations:

The good news is that in the last 18 months, several new manufacturers have come on board with purpose-built .357 SIG stuff, in both components and in plinking and defensive factory loads.  I  have been able to buy dedicated .357 SIG bullets in 124 or 125 grains from D & J Bullets Inc., as well as Wideners, Dillon and a few mail order outfits from Shotgun News and the Gun List. I am most satisfied with the price and quality from D & J Bullets and Widener's, and they are also real gun owners, real shooters and gun activists, as well as being "sales folks."  To me that means a lot, as I often find that when I ask questions about .357 SIG, many of the sales types have no idea what I am asking for.  Admittedly, I am now considered a "subject matter expert on .357 SIG," and I assume that I know more than the average ammo salesman. But when I ask someone who sells ammo for a living, "do you have .357 SIG ammo," and they say, "Sure we have 4 different .357 Mag loads, what do you want?"  or "SIG?.... .357 SIG.... you mean .357 SIG... Ah well duh... is that for SIG's?"  Bone Heads!  Sorry, it still irks me.   Almost as bad as when the Hired Gun Writers say "It's just a necked-down .40!"

The new .355 diameter bullets specifically designed for the .357 SIG are a tad longer and seat better.  I recommend the Federal- or the Speer/CCI-made bullets and cases.  We have had the best luck reloading the Federal cases and have now reloaded several hundred of them for the 20th time.  Please note this is for testing and evaluation purposes only.  We are not that cheap.  The odd thing is that the performance numbers are extremely consistent in all of our .357 SIG loads; typically within a 5 or 6% SD (Standard Deviation) of one other, and I have never had a reload that is that consistent.  Hell, at The Gunnery Network collectively we are hard pressed to remember a factory load that is that consistent!

We have now played with several loads and bullet sizes, and have always found, and then returned to, the original 125-grain bullet for performance and accuracy. The inherent accuracy of the 125-grain projectile traveling at or about 1350 FPS (Feet Per Second) is remarkable. We have also used several "drop in" type .357 SIG Barrels in guns that were made for a .40 S&W, and the group sizes were reduced, typically by 40%, by just using off-the-shelf, "white box" .357 SIG loads (like Winchester, PMC or Speer/CCI FMJ-TCJ Stuff).  Even the Glocks were accurized by dropping in a .357 SIG barrel, and Glocks are not known for tight groups.  Glock owners say that Glocks are great for parking in a snow drift under a 4x4 truck, but Glocks are not inherently accurate.   At least not by a SIG user's standard.  By the way, I have never met a SIG owner stupid enough to drive a 4x4 over their SIG.  If I ever do I will let you know how things turn out.  :)

When we use our hand loads, the group's size typically drops to less than 60% using the exact same gun with a replacement .357 SIG barrel and cheap ammo. As an example, we took an off-the-shelf Glock in .40 S&W that typically fired 3.5 inch groups at 25 yards. We did nothing to it except drop in a Bar Sto barrel in .357 SIG. Now it shoots a 1.7 inch group consistently at 25 yards! It can also now shoot a 5.5 inch group from a bench rest at 100 yards. That's what you can expect in a .357 SIG handgun, and of course, if it has a real SIG wrapped around it, the accuracy is even better.

I switched to .357 SIG early on in it's development, and have been praising it ever since. In the last two years or so, several federal and state law enforcement agencies have made the same conclusion and switched to it as well.  The original load specification calls for a Federal .357 SIG case and a Federal 125-grain bullet. Note that the good old 9mm /.355 diameter bullets will work just fine in a .357 SIG, as long as you get them seated properly, but the new purpose-built Federal and Speer .357 SIG bullets (also .355 in diameter) are a tad longer and are specifically designed for the short crimp space of the .357 SIG case. They are also designed to prevent excessive fragmentation that is caused by the high velocities and impact energy, typically above 1300 FPS and 550 Foot Pounds.

I would stay away from the 147-grain loads as they really defeat the design intent and performance cone of the .357 SIG. I would also strongly recommend the use of Accurate Arms Powder Company for the powder, and especially AA Number 9 if you like to use compressed loads. As of now the AA#9 is unbeaten in our tests. I think the full case helps with the load somehow, but this is far from a scientific conclusion.  In fact, most of the name-brand powder out there will work just fine in a .357 load, but most people who take the time to read this and reload for .357 SIG want the extra performance we have found with AA#9.

If you go with cast bullets or lead you need to cast or buy one of the many .356 diameter bullets as the lead/cast will compress when crimped and this makes it close to the specified .335 diameter.  I do not recommend cast bullets in modern handguns and would advise you all to stay away from lead bullets if at all possible.  TCJ and No Leads are now readily available for pennies more per hundred and your health, the health of you gun and that of your grandchildren may depend on this approach.  Yeah yeah yeah, I know lead occurs "naturally" on planet earth, but it does not occur naturally on you hands, your hair, your beard, your children and your house.  Just say NO LEAD!

The Hot Tip: Since the .357 SIG is a bottlenecked cartridge, you should lube the case lightly before resizing, etc. Afterwards, tumble/dry the completed brass for around 15 minutes to get the lube off. This may at first seem like a bummer, but a lot of competitors lube even straight walled cases, to make it easier for them. In several reloading videos I have, they say that many of the factories pre-lube everything.

FYI: I do not load my own "Defensive Ammo", except for what I call "Contingency Ammo" for my AR-15s and some .308 "Trunk Gun" stuff, as I just like to be extra careful with my handgun defensive loads. We keep a couple of French Foreign Legion type MAS 56's in both of our vehicles, thus the "Trunk Gun" Reference.  I have had to use my SIG 2 times in the last year alone and have had to use it way too many times in my career. Better safe than dead on the defensive/CCW loads. 

For defensive and CCW .357 SIG ammo, I buy and use Speer Gold Dot in 125 JHP, and when I can find it, I buy PMC/Eldorado Star Fire in 125 grain. I also use the Federal PPD and Federal Hydra Shok's as they are most commonly on the shelf, but find that the perceived recoil and flame in these rounds is excessive.  Could you use Federal PPD as CCW ammo?  Yes, but the Speer Gold Dots, Federal Classic in 125 JHP and the PMC/Eldorado Star Fires are just as effective ballistically and are more pleasant to shoot.  I get about an 18-inch flame from the new Federal PPD stuff, as well as much more perceived and measured recoil.  A well designed and well loaded .357 SIG round should not feel much different than a defensive 9mm round when fired and you should feel less perceived recoil than a .40 S&W round.   I would stay away from the Armchair Commando Ammo [read COR-BON, Triton, MagSafe & Glaser].  Please see the article by Shawn Dodson, Director of the Firearms Tactical Institute on this at URL: firearmstactical.com or at Todd Green's excellent Calibers Web Page at  http://greent.com/40Page.  The M.D. Smith Reloading Page has some good, safe and effective load data online for the .357 SIG, and I have used and still use a very similar formula in my "Action Shooting and Plinking Loads." You can find his page and several sources of reloading supplies and info at:

URL: http://www.GunneryNetwork.com/reload.html

WARNING. After you initially set up your .357 SIG dies, be sure to use the thumb pressure test. Put the bullet end of the cartridge on a hard surface and press hard from the primer end. Make sure the bullet does NOT move. Since the .357 SIG only has 1/8 inch of neck to grab the bullet, make sure not to expand the neck more than necessary to seat a bullet. And make sure to apply a firm taper crimp. If the bullet moves down/back into the case, severe pressures will result.

Editors Note: An article has been added titled "357 SIG handload reliability...controlling headspace".  Written and Copyrighted by Joe D'Alessandro.  The Article is at URL: http://www.GunneryNetwork.com/sig/001.htm, it was originally published at www.RealGuns.com and is re-published on "The Gunnery Network" with the author's permission.   The Staff of GunneryNetwork.com wishes to Thank Joe for his contribution.

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