K-Frame Forcing Cone

[Stephanie B]

The Ayoob Files

The book is now a collector's item. Paperback copies are going for around a hundred dollars and up.

[deputyG23]

Forcing cone erosion is an issue in heavy use revolvers of any caliber when lighter than standard weight bullets are driven at higher than standard velocities. You're literally blasting the forcing cone and top strap with high velocity blasting media and you're wearing out the machine. What's more troubling than that is forcing cone splitting. The K-frames in .38 and .357 are more susceptible to this because the barrel root is much thinner than the N or L frame cones and doesn't withstand the wear the larger frames do. When the forcing cone splits, that barrel is done. Erosion can be addressed by setting back the barrel a thread and re-cutting the cone. Splitting requires a new barrel.

More concerning is the growing lack of pistolsmiths who actually know how to do those processes well (or at all) in this 21st Century AND the growing lack of spare parts.

If you have one (or many) of these treasured revolvers, I'd suggest you shoot standard loads, with lead or plated bullets and to not see if they'll digest as many rounds as your Glock 17 will. Those of us old enough to remember carrying and training with them also recall we didn't do 500-1000 rounds per day with them. There was a reason for that.

About 200-250 rounds a day was the limit for us back when we were doing revolver training in Basic Jailors School here in VA. With the low bid 158 grain soft lead swaged SWC reloads we used, the guns got sluggish to the point that they became harder to manipulate due to all of the burnt powder, lead splash, and bullet lube. The Smith Ks and later Ls usually lasted longer on the firing line before requiring a good scrubbing than the Ruger Six series that some deputies bought for work. One female officer had a Police Service Six that would not go past 150 rounds without becoming inoperable.
It would have been interesting to see how long those revolvers would go now with the 130 grain jacketed ammo now in common use.

[03RN]

Forcing cone erosion is an issue in heavy use revolvers of any caliber when lighter than standard weight bullets are driven at higher than standard velocities. You're literally blasting the forcing cone and top strap with high velocity blasting media and you're wearing out the machine. What's more troubling than that is forcing cone splitting. The K-frames in .38 and .357 are more susceptible to this because the barrel root is much thinner than the N or L frame cones and doesn't withstand the wear the larger frames do. When the forcing cone splits, that barrel is done. Erosion can be addressed by setting back the barrel a thread and re-cutting the cone. Splitting requires a new barrel.

More concerning is the growing lack of pistolsmiths who actually know how to do those processes well (or at all) in this 21st Century AND the growing lack of spare parts.

If you have one (or many) of these treasured revolvers, I'd suggest you shoot standard loads, with lead or plated bullets and to not see if they'll digest as many rounds as your Glock 17 will. Those of us old enough to remember carrying and training with them also recall we didn't do 500-1000 rounds per day with them. There was a reason for that.

How safe do you think 158 hardcast bullets going 1100-1200 fps are?

[Wayne Dobbs]

How safe do you think 158 hardcast bullets going 1100-1200 fps are?

In a K-frame, they're not great from a wear standpoint. If you limit them to a few, that's not bad, but there shouldn't be a steady diet of these loads in guns that there are no more parts for to speak of. Edit: Please tell me you're referring to .357 Magnum loads, too.

[OlongJohnson]

My research on the topic in preparation for care and feeding of a Ti cylinder indicates that powder selection makes a big difference in flame cutting.

Li'l Gun and H110/W296 are double-base powders, and burn much hotter, tending to generate flame cutting, while delivering the highest velocities in .357M and .44M.

4227 is a single-base powder. It wants to be near high-end loads to achieve more complete burn (will still leave some unburned debris behind at max in .357M), but is cooler burning and will significantly reduce the rate of flame cutting. It releases less energy and won't deliver the top-end velocities of the ones mentioned previously. Longer barrels may leave less unburned 4227 material.

A heavier bullet is charged with less powder, which helps. The longer bullet accelerates more slowly and has farther to travel before the base clears the throat and exposes the cylinder gap to the burning charge, so it's a win-win as far as giving the charge time to get more burning done and minimizing flame cutting.

My strategy on .357 loads that will best preserve a non-consumable revolver is 180gr bullets on top of 4227. Haven't worked it up yet, but have put money down on materials. That's primarily in context of an N-frame and GP100s.

I figure the double-base powders and top velocities are for Contenders, carbines and revolvers that are regarded as consumable sporting equipment.

A better long-term strategy for K-frames is just to run .38SPL (or +P) level loads with 158gr bullets. You can still do this in .357 cases to avoid the carbon ring in a .357 cylinder, and it can be done with old school powders that won't cause problems with erosion.

If I was going to go high-volume on a K-frame, I'd search for a non-defective 67-6 (current revision, starting in 2004). There are quite a few reports around that the two-piece barrels on the -6 are actually more accurate than the one-piece on -5 and earlier.

[03RN]

In a K-frame, they're not great from a wear standpoint. If you limit them to a few, that's not bad, but there shouldn't be a steady diet of these loads in guns that there are no more parts for to speak of. Edit: Please tell me you're referring to .357 Magnum loads, too.

Yes,. 357

I typically run pretty conservative on reloads. I'm just looking for good working loads.

Frank Glenn was pretty adamant that standard velocity .357 won't cause any undo wear on the m19 I already had him fix.

I'm also not talking 1k round days. I think 2-300 us the most I'd shoot at a USPSA around here. Typically it's a 50-100 round range session per week and I've found 6.4 of unique to give a mild but more than a .38 load that I figure is pretty close to 1100fps and shooting a mid range load DA really feels like I'm working but isn't overboard.

I just shot some reloads with a 158 swc over 13.5 of 2400 that felt milder than factory federal 158 JSP. Skeeter rated them around 1200fps.

[revchuck38]

@03RN - Way back when, I loaded 6.8 grains of Unique under a 158-grain hardcast LRN for IDPA ESP, and it ran ~1080 fps from my 4" 681.

[03RN]

@03RN - Way back when, I loaded 6.8 grains of Unique under a 158-grain hardcast LRN for IDPA ESP, and it ran ~1080 fps from my 4" 681.

Thank you, it seems the most current unique runs a bit warmer. Looking at data from 10 years ago shows lower numbers than current. I really need a cronograph.

But even at 1000fps ish I'm happy.

[Totem Polar]

One way to deal with the issue is to buy a bunch of K-frames. Just saying.

[willie]

Sluggishness from lead bullet loads is almost always a result of debris under the extractor star. Range guns already have enough looseness not to be slowed down by crud on fronts of cylinders. Holding revolvers with barrel pointing to high noon and smartly hitting extractor rod alleviates the problem somewhat when ejecting empties. Cleaning under extractor stars is mandatory. Crud will accumulate. If instructors do not make students clean here, then they will not. Some instructors are unaware of the problem and how to alleviate it.