S&W forcing cone damage

[PinnedAndRecessed]

On another forum I was told that the K frame Smiths were subject to forcing cone damage with high velocity, light weight bullets.

It seems that when the Model 19 was introduced police departments favored the magnum loads with 125 grain bullets. Turns out the magnum 125s hit the forcing cone faster than heavier bullets and thus destroyed the forcing cones.

So Smith said to only use 158 grain mags since they start slower.

My current favorite load is a 125 grain plated bullet ahead of 8.0 grains Unique which gives me only plus P velocities. I think. I've never actually clocked it.

My question: if I'm using 125 gr plated bullets (note: that's softer than jacketed) at plus P velocities, that shouldn't produce the same damage as full-charge magnum bullets, should it?

#2: How many rounds of full-charge magnum ammo does it take to destroy the forcing cone?

#3: If it's the velocity + light bullet that kills the 19, then why isn't this a factor in the N frames?

thanx.

 

[Jim K]

I will give it a try, though I am not sure how satisfactory my answers may be.

On #1, 8 grains of Unique is a fairly hot load (1275 fps or so) but I would have no concerns about any revolver damage for anything like the foreseeable future; barring anti-gun laws, your grandchildren should be firing that gun. The loading manuals show 10 grains of Unique as maximum with that bullet. (You do have loading manuals, don't you? If not, why not?)

I am not sure I can answer #2; it is not certain that any given cone will ever be destroyed, just that cases are known where they have been.

I can answer #3. The L and N frames are larger, allowing a thicker barrel and hence a thicker area around the forcing cone. This does not prevent erosion from hot loads, but it does prevent the splitting sometimes seen with the smaller frame guns.

Jim

 

[PinnedAndRecessed]

Thanx Jim.

My Lyman manual says 7.0 Unique is minimum (at 990 fps) and 9.7 is max at 1359 fps.

My Speer manual says 8.6 is minimum (1313 fps) with 9.1 max (1390).

An old Hercules manual just gives one load: 9.6 at 1585 fps.

So I just tried to grab a middle of the road load at 8.0 gr Unique and guessed it was about 1000 fps.

I guess I'll load the next batch down to 7.0 grains. I hesitated doing that because that's much lower than what Speer says is minimum.

 

[4thHorseman]

PinnedAndRecessed my reccomendation to you is to just shoot away. The amount you'll need to damage a forcing cone with factory loads will be considerable.
To take a wild guess to help solve you question, probably in the neighborhood of 20,000 rounds you'll start to see damage that may need attention. If you are like most of us with a lot of guns that we alternate at the range, it's unlikely that'll happen anytime in the near future.
Shoot away, and isn't that why you got it to begin with? Enjoy your S&W pal.

 

[buttrap]

Yep it will go out of time shooting hot loads before you have forcing cone issues.

 

[GooseGestapo]

The forcing cone erosion and/or splitting is primarily an issue arrising from HEAVY use of the 125gr .357mag "factory" level loads.

A K-frame gun can occasionally after many thousand rounds crack the barrel at the forcing cone on the bottom because of a relief cut to allow the gas ring of the cylinder to clear it upon closing the cylinder (Have cut some rebarreling for PPC revolvers w/heavy barrels). At this "thinned" area, after some erosion has set in, the metal will also become stress harded allowing/causing the barrel to crack. If the crack is not too deep, the barrel can be "set back" a thread or two and the forcing cone and barrel/cylinder gap re-cut, putting the barrel back into use for another round of action.

A lot has been made of this, but I was an active duty L.E. officer from late '70's till '04 and only saw a few that have cracked. They were all range guns used for training and qualifying new recruits by agencies that trained and qualified with magnum ammo. I was told once by a range officer/armorer that it was happening at around 25,000rds. He kept several barrels on hand, and it takes about 15-20minutes to replace the barrel. (providing you have the equipment and spare barrel on hand- some discontinued models can be difficult to impossible to get replacement barresl for)

[I have cracked a one myself, but from "firing out" a squib load. NOT something I recommend doing. I only did it because it was a PPC regional match and the entry fee alone was greater than my cost to replace the barrel. Even with a 148gr WC match load, this will buldge a heavy match barrel and can DESTROY a J-frame revolver. I have gotten away with shooting out a couple of squibs. Even won a couple of the matches where its occured, making the "gamble" worth it.]

Even with the L and N frame guns, I've seen modest to considerable throat erosion (forcing cone looks like it has been sand-blasted through a magnifying glass, and the edge of the barrel face will show rounding off [bore side, not outside edge] but accuracy and velocity is not significantly affected.

Forcing cone cracking with the K-frame was just something that occasionally "happened" when shooting a large volumn of Heavily loaded lightweight jacketed bullet Magnum loads.

But, from my personal perspective, I much prefered to carry the K-frame guns to the L-frame or a Glock M22 and "46!" rds of ammo, that I never needed!!!. After 12-15 hours on duty, 8-10 ounces up to to 2+ pounds "extra" on your gun belt will make a HUGE diffence! A slightly worn "eroded" forcing cone matters not a whit !!!!!
(I never even needed ALL of the 18rds I carried with the revolver, although I occasionally DID use the extra couple of .38 lswc's or shot capsule loads I carried in my pockets!)

I then, and now, still prefer the revolver!

All my carry and hunt guns are revolvers. By choice.

(I have 3 S&W Perf. Ctr. SemiAutos I shoot in competition. I won't risk losing a $1,250 gun while getting in/out of a boat, ect. My $125.00 Ruger Sec.6 is a whole different matter!)

 

[Old Fuff]

P&R:

I don't think you have to worry about throat errosion with the load/bullet combination you are using. However I would suggest that you experiment a little to see if you couldn't find something that was more accurate. In general, S&W barrels that have a slow rifling twist do better with heavier bullets. Other manufacturers use a faster twist. Anyway, it might be fun to try something else with maximum accuracy in mind.