K Frames: Is it the light bullets or the high pressure causing problems?

[Thunderball]

I'm sure this subject has been beat to death before, but here goes anyhow.

After reading the article at

Use of Magnum Loads in S&W Model 19 and Other K-Frame Magnums

I am more confused than ever. it seems like this guy states that the problem with light bullets is there relatively short length and that short length allows gas to prematurely escape......well this is what he says: "The bearing surface length of the 125 grain bullet is shorter than the bearing surface of the 158 grain bullet. This difference means that as the 125 grain bullet leaves the case there is a gap between the leading edge of the bullet sealing surface and the cylinder throat. As the short bullet makes this jump, combustion gases and powder are permitted to blow past the bullet and prematurely escape into the barrel. The 158 grain bullet essentially seals off the cylinder as it leaves the case and enters the cylinder throat. More complete combustion of the powder is accomplished. Temperatures of the gas as it enters the barrel are lower and the combustion environment in the barrel is not oxygen rich as is the case for the prematurely escaping combustion gas. Checking the dimensions of my 19-3 confirms that for the 158 grain HP bullet, the leading edge of the bullet is engaging the lands as the base of the bullet has just left the case mouth and is flush with the cylinder throat. For the lighter HP bullets of 115 to 125 grains, there is a gap of approximately 0.15 to 0.12 inch, respectively."

Does this mean that a 115 grain .38 loaded at normal pressures is more harmful than a 158 grain .357 magnum loaded to full magnum pressure?

 

[Alk8944]

The issue is with S&W K-frame .357 Magnum revolvers using full power, jacketed, 125 grain ammunition. Not .38 Spl or any other .38 caliber anything.

There is a lot of speculation as to the true cause, but the result is the barrel shank cracking at the bottom where there is a flat cut for yoke clearance. There is a large amount of anecdotal evidence that there is a real problem with this combination as well as frequent posts starting, "Where can I get a barrel for my Model 19, it has a cracked forcing cone?" The short bullet allowing blow-by is a red herring. If that were true, than the 110 gr. bullets would be at least as bad a problem as 125s, and they just don't seem to be.

It is the overall dynamics of the load placing too much stress on a weak portion of the barrel. Doing anything to change the load, lower velocity, lead bullet, heavier bullet, etc, and the hazard seems to go away.

 

[WR Moore]

The model 19 was designed & produced at a time when most qualificaton and/or practice shooting was with .38 wadcutters or something similar. There were very few magnum rounds actually shot from the weapons, even in police service.

The Newhall incident in the mid 1970's changed police training and qualification forever. Practice and qualification was with full power issue ammunition. No more patty-cake rounds, if magnum ammo was issue, it had to be used for all practice, qualification and training. Given this type of usage, forcing cone failures became more frequent.

The development and adoption of the 125 gr JHP load happened at about the same time. FWIW, this load produces much higher pressures (or at least it did in the references I checked) than the 110 gr load.

 

[dasandman]

So does this mean that reduced loads such as the Hornady 125 gr. critical defense load are ok to use in the k-frames?

 

[flop-shank]

The short bullet allowing blow-by is a red herring. If that were true, than the 110 gr. bullets would be at least as bad a problem as 125s, and they just don't seem to be.

Most factory 110s are downloaded. Really they're somewhat like managed recoil loads along the lines of Speer SB, but perhaps a little hotter. I'm not saying you're wrong, Alk, but do you know whether or not full house 110 gr. JHP loads, such as Corbon offers, bust K frame forcing cones too?

 

[Alk8944]

Most factory 110s are downloaded. Really they're somewhat like managed recoil loads along the lines of Speer SB, but perhaps a little hotter. I'm not saying you're wrong, Alk, but do you know whether or not full house 110 gr. JHP loads, such as Corbon offers, bust K frame forcing cones too?

Never heard of one, have you? Never heard of any anecdotal accounts of this either that I recall.

Current 110 gr .357 may be downloaded from what it used to be, but the same can be said about just about all current .357 ammunition. I never have made a practice of shooting light-for-caliber bullets in any handgun, but have shot some. Back in 1991 or 2 when a local store was having financial problems and dumping some inventory I did buy several boxes of 110 gr. Winchester ammunition for just about what the brass would cost. That stuff was pretty warm. The muzzle blast was virtually identical to .30 Carbine in a Ruger Blackhawk. Since I had no intention of buying more, and really didn't care, I didn't chronograph it. Wish now I had just to know.

 

[flop-shank]

Alk, thanks for the reply. I've never heard of 110 gr. problems in K frame .357s. If I did carry a K frame I'd avoid the 125 gr. issue entirely by using 145 gr. Silvertips, or a handload with a heavier bullet such as the Sierra 140 gr. JHP.

I've fired Winchester's and Remington's 110 gr. JHP loads. I would describe them as a 7/8 power load based on how they felt to me. You may be on to something in that the dynamics of the 110 gr. loads are different and probably don't hurt K frame guns.