We've all heard about the cracked forcing cones that come from shooting hot 125 grain jacketed ammo in a Model 19.
Does that problem happen with other, lightweight projectiles in the Model 19?
I'm wondering, how fast can I push the Lee 105 grain SWC, powder coated, out of my 357 without compromising the forcing cone?
This bullet is very accurate out of anything I've shot it out of. So far, I've kept it to 38 Special loadings. Don't know if it would be wise to push it to 357 speeds.
It would be the middle bullet in this picture.
Thoughts?
Cracked forcing cones do happen in K frame .357 Magnums, not just the Model 19, but the fact that the Model 19 is most associated with the phenomenon speaks to how the myth that it’s caused by 125 gr bullets got started.
The Model 19 was a very common law enforcement revolver when the 125 gr bullet came into more common use in law enforcement. In fact the Model 19 was designed for law enforcement use, and significantly, it was designed at a time when virtually all practice was done with .38 Special with .357 magnum normally reserved for duty use.
However, two things happened around the time the 125 gr load became the preferred law enforcement load in .357 Magnum.
First, law enforcement agencies started to get sued for under training their officers by training with .38 Special and carrying .357 Magnum. Consequently they switched to practicing with the same ammo they carried, and the Model 19 (and the other derivative K frame .357s) were not designed for a steady diet of .357 Magnum loads.
Second, powder companies started making colloidal ball powder that were inexpensive (they could be made from WWII surplus canon powders), quick to make (about 10 days compared to two months) and different lots could be mixed to produce powder to a wide range of specific specifications.
These same colloidal ball powders also happened to produce around 50-100 fps more velocity in magnum revolver rounds like the .357 Magnum in 3-6” barrels so they became popular from a performance standpoint.
Given the powder charges were also about twice as much as the medium speed flake powders that had been used before they also produced about 1/3rd more recoil, and of course when shooters felt that increased recoil they felt they had a much more powerful round, even though the velocity increase was frankly minimal.
However, the use of colloidal ball powder now meant a lot more powder was flowing through the comparatively thin forcing cones of those Model 19 revolvers in a mix of plasma, gas, partially burned, and unburned powder grains. Those partially burned and unburned grains were also quite course.
The 125 gr loads had the most powder due to the lighter projectile weight with powder charges in the 20-21 gr range. The heavier 158 gr loads had powder charges in the 15-16 gr range, about 25 percent less with a consequent 25% reduction in forcing cone erosion. It was still a lot more erosion than with the older flake powders but it was 25% less than with the 125 gr bullets, and the 158 gr bullets were not as commonly used in .357 Mag law enforcement loads at that time.
That forcing cone erosion matters as the V shaped cuts caused by the increased erosion of those large charges of course colloidal ball powders creates stress risers that ultimately create cracks in the thinner area of the forcing cone where the outside of the forcing cone was milled flat to provide clearance for the crane.
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At some point some gun rag writer noticed the correlation between forcing cone cracks and 125 gr bullets and came to the poorly informed conclusion that it was the shorter 125 gr bullets causing the cracks.
He or some other gun rag writer decided that it was caused by expanding gasses racing around the shorter bullet, reaching the forcing cone first and preheating it, creating more damage when the bullet arrived and impacted the forcing cone. That person clearly had little or no information on thermodynamics or heat transfer on those millisecond timescales, and clearly put no thought into the powder being used and shear volume of powder now being used.
Thus a myth was born. The powder companies using colloidal ball powders probably had it figured out pretty quickly but they were not going to cop to it, mess with their profit margins and potentially face not only loss of sales but potential product liability.
After all the erosion caused by large changes of colloidal ball powders doesn’t just affect Model 19s or even S&Ws but also caused excessive erosion in Ruger Speed/Service/Security Six series forcing cones as well, it just rarely if ever caused cracks as the forcing cones were so much heavier. Ultimately S&W responded similarly with the L frame and its heavier forcing cone without the relief cut.
Few people seemed to ever ask why if cracks were the result of the shorter 125 gr bullet (compared to the 158 gr bullet), why didn’t 110 gr bullets cause issues with cracks? The fact that what do not is more proof that it’s the powder not the bullet or it’s length. The reality is that loads using those lighter bullets are just not efficient with those slow burning colloidal ball powders so they are just not used to any great degree. If you doubt that look at a reloading manual from a bullet manufacturer and note the lack of loads using Win 296/H110 for 110 gr bullets.
Today over 50 years later that myth that it’s the bullet and not the powder still persists. On the positive side even with Model 19s (and other revolver) modern metallurgy has reduced the erosion from those colloidal ball powders so the problem isn’t as severe as it used to be (or still is with vintage revolvers).
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The short version is that if you worry about forcing cone cracks, stay away from loads using colloidal ball powders. You’ll give up maybe 50-100 fps in velocity but you’ll also have about 1/3rd less recoil and you’ll be reducing forcing cone erosion and cutting off the top strap to almost nothing.
