This topic constantly surfaces and is often brought up especially when members buy their first K magnum, it's always been the consensus opinion to avoid light magnums but mostly from anecdotal stories.
Yesterday in a thread discussing this same question member Hairtrigger posted a link to the best most thorough explanation of every angle of the issue, how it surfaced , when, why and what the solutions were, it is a long read but the story is not simple to explain.
If you have 20 minutes to read the whole story but it's almost impossible to tell the tale in a short thread except yes avoid light loads.
Enjoy.
The Smith & Wesson L-Frame Story – RevolverGuy.Com
That linked story was a great read. Lots of interesting info there.
One thing they mentioned that caught my eye was that in the mid / late 70s (which is when K frames cracking forcing cones became a bigger issue it seems...) that the winchester 125gr jhp load was using a bullet sealant that could sometimes create a ton of pullet pull. Something like that can REALLY spike cylinder pressure. They mentioned one cartridge example that required 385 lbs of force to pull bullet. An outlier statistically of course, presumably most werent nearlythat bad, but shows they (high bullet pull from sticky case sealant) were out there.
They mentioned a "former SW employee" in that time frame who saw a new K forcing cone crack in 11 rounds of that ammunition.
That made me think of something i dont -think- has been mentioned in this thread / in that article (apologies if so). Ok, so it was common for police agencies (and civilian shooters too), to shoot a mix of 38 special and 357 mags. Shooting 38s in a 357 cylinder does leave fouling at the end of the chamber, particularly if the 38 load is a soft (unjacketed) lead bullet. That fouling builds up and at some point it will make it difficult or impossible to put 357s in wo cleaning the cylinder, since the longer 357 case runs into the fouling at the end of chamber.
If the cylinder is fouled from shooting 38s, and someone puts in 357s, and they have some resistance but not enough to seem like a real problem (if you have to use a hammer or other object to push cartridges in, it would be a sign to any reasonable person that something was off). But lets say the fouling is significant but not enough to make it too hard to put cartridges in. Well, what im wondering is if there would be enough fouling there to make it harder to get bullet out of case when firing.
If case has a harder time releasing bullet due to insufficient clearance around case to open up, it can really spike chamber pressure. I wonder if that was one of the factors that contributed to K frames cracking forcing cones? (There were obviously a multitude of factors...which is why sometimes it happened early, sometimes never happened... just determined by whether the "swiss cheese holes" happened to lineup just right... or not).
I know for a fact (seen it in my own rifles), that a chamber w a neck thats just slightly too tight* can really spike pressure. Can make a big difference. *and too tight doesnt necessarily mean that extra force is required to seat cartridge, that theres interference / no clearance. Chamber can be almost exact same size as cartridge neck, maybe a few .0001s of clearance, but not a thousandth or two thousandths of clearance that most rifles seem to like as a minimum (and we're talking target rifles, handloaded ammunition, being fired on a range... not in field / hunting scenarios, let alone combat conditions.. with who knows what ammo.. those need more clearance).
Need a bit of room for case neck to expand, smoothly release bullet or you'll see pressure spikes.
Anyways, didnt mean to write such a book but just seemed interesting to me
Wonder if fouled chambers from 38s helped contribute to this.
