I am about to venture into reloading 357 magnum for a model 19 and a model 66. I intend to use Hodgden tight group only due to its ready availability. I have loaded 44 mag 45 ACP, 9 mm and all of the shotgun gauges. I intend to download 158 grain semi wadcutter's. so as not to over stress the K frame and forcing cone. Any thoughts on the tite group in 357? Any preferable, powders, or suggested loads?
Let's talk about one of the most enduring myths in .357 Mag history.
It has long been asserted that forcing cone cracks in K frame .357's are the result of the shorter 125 gr bullet. The working throry was that the shorter bullet allowed gas to get around in front of the bullet and preheat the forcing cone before that shorter bullet got there. To put it simply that whole theory has zero basis in fact or reality.
Why did it become a common belief? Timing and correlation, between revolver, powder, bullet choice, and training.
Revolver
The Model 19 was designed in the mid 1950s and was introduced in 1957 as the ideal law enforcement revolver, balancing strength and weight, at a time when the l58 gr LSWCHP was the bullet of choice, and medium burn rate flake powders were the norm.
Powder
However, around 1960, Olin started reworking WWII surplus canon powder into small arms powder by dissolving it in ethyl acetate containing small quantities of stabilizers and additives. The resultant syrup, combined with water and surfacants, is heated and agitated in a pressurized container until the syrup forms an emulsion of small spherical globules of the desired size. The ethyl acetate is distilled off as pressure is slowly reduced to leave small spheres of nitrocellulose and additives. This is what gives these powders their common names as "ball powders" or "spherical powders".
These spheres can be modified by adding nitroglycerine to increase energy, rolling to a uniform minimum dimension, coating with deterrents to retard ignition, and coating with burn rate inhibitors or graphite to improve flow characteristics during blending.
The resulting individual powder batches are then tested for their burn traits and are then mixed with other lots to produce the desired burn characteristics in the final lot to the customer specifications.
The advantages of ball powders are:
- they are cheap to produce, particularly with surplus powders, although the same process works with newly made nitrocellulose;
- they are fast to produce, taking about 40 hours compared to about 2 weeks for a flake powder; and
- they are much safer to produce as most of the process is done wet.
In 1962 Olin started making 295P, which was was marketed by Hodgdon as H110. (295P as reformulated in 1973 as 296, and it continues to be marketed ever as Win 296 and H110.) This powder was used in the .30 carbine as well as in magnum pistol cartridges like the .357 Magnum.
***Note this was about 5 years after the introduction of the Model 19 / K-frame .357 revolvers.
By the late 1960s it had become very popular with makers of .357 Mag ammunition as ball powder was much cheaper to purchase, and it also gave between 50 fps (3" barrel) and 150 fps (6" barrel) more velocity. In terms of marketing that was a plus, but a side benefit was the much heavier powder charges used also produced about 35 percent more recoil so it felt more like a magnum load. More on this later.
Bullet choice
By the mid to late 1960s, more and more law enforcement agencies started transitioning to jacketed hollow point 125 gr hollow points instead of 158 gr loads. And of course these new loads, designed for 4" and 6" duty revolvers, used ball powders to maximize velocity as opposed to the flake powders used in the older, traditional 158 gr loads.
Law enforcement training practices
When the Model 19 was designed, agencies using .357 Mag normally trained with .38 Special and only carried .357 Magnum for duty use. Some used it for qualification, others qualified with .38 Special.
Unfortunately in the late 1960s and early 1970s, agencies started getting sued for 'under training officers by training and sometimes qualifying with .38 Special and then carrying .357 Magnum. That led to a training and qualifying with .357 Magnum.
So...the Model 19 (and Model 13, Model 10-8, Model 66, etc) went from a split of maybe 5-10% .357 and 90-95% .38 special to 100 percent .357 Magnum.
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Then forcing cones started cracking...
Perceptions matter, and the only things people saw were the switch to the 125 gr bullet in .357 Magnum loads and the greater use of .357 Magnum loads.
Thus arose the myth that it was the shorter 125 gr bullet that was causing forcing cone cracking.
But it was really the change to ball powders.
Consider a maximum load of a ball powder with a 125 gr JHP bullet. With cannister grade H110/Win 96, you'll see published loads with a max around 20 grains (some sources a grain or so higher but that's not the point). That compares to a max load around 16 grains for a similarly constructed 158 gr bullet.
In other words, the switch to the lighter/shorter bullet increased the powder charge from 16 to 20 grains, a 25 percent increase. That's 25 percent more plasma/gas/partially burned powder flowing through the forcing cone with the same type of powder.
Even more significantly, lets compare the effects of changing the powder.
Let's compare that 20 grain max load of Win 296 with a max load of a medium burn rate (by pistol standards) powder like Unique. A max load of Unique with a 125 gr JHP will be about 8.5 to 9 grains. In other words with Win 296 you'll gain 50 to 75 fps more velocity in a 3" to 4" barrel, but the mass of plasma/gas/unburned powder flowing through the forcing cone is around
225 percent greater.
Another old myth is that pistol powder is completely burned in the case before the bullet ever exits. To be fair that's closest to the truth in cartridges like the black powder era developed .38 Special and it 1/8" longer .357 Magnum derivative, where they both have lots of internal diameter - when they are using a small volume of a faster burning flake powder.
With a very slow burning (by pistol standards) ball powder like H110/Win 296, there is a lot of partially burned and even unburned powder flowing through the forcing cone. Worse, that colloidal ball powder is pretty abrasive.
What happens when you push 225 percent more powder mass, with a much higher percentage of much more abrasive powder through a forcing cone? You get
at least 225 percent more erosion in the forcing cone.
Those little V shaped erosion cuts get bigger with round count and they create a stress riser. In the Model 19, the outside of forcing cone is milled away to a flat spot to allow for clearance of the crane. That flat spot is the thin spot of the forcing cone and the area most susceptible to cracking once forcing cone erosion starts to happen.
If you're brain is saying "that's bovine fecal matter", consider why if its the shorter bullet causing the erosion and cracking, why isn't it an issue with much shorter 110 gr .357 Magnum loads? The reason is that those 110 gr loads are not efficient with the slow burning ball powders, so they are not used with 110 gr bullets. Those loads use medium burn rate flake powders. In addition, they are usually low recoil loads, designed for short barrel revolvers, where ball powders are even less efficient, and where low recoil is a feature, one that would be undercut by doubling the powder charge and increasing total recoil by probably 40 percent.
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In short, the secret to long Model 19 / .357 K frame life is to just avoid colloidal ball powders. Use whatever bullet you want. You'll lose very little velocity in a 2 1/2" barrel, around 50 fps in a3" barrel, around 75 to 100 fps in 4" barrel and around 150 fps in a 6" barrel, but your forcing cone will see almost no erosion, and thus you won't have issue with cracking, and about 35 percent less recoil which also helps overall revolve life.
If you really need maximum performance, use a ball powder but use a heavy 158 gr bullet to reduce the amount of powder and forcing cone erosion. And limit the use of those colloidal ball powder rounds.
