Forcing Cone Erosion

[PaperPatch]

This is my first center fire handgun purchased new in 1985. It's also the first handgun I loaded ammunition for; with many pounds of powder going down the tube. These days, it has begun spraying gas back at me upon firing...and as I understand the eroded forcing cone is the culprit. Time for a trip to Smith and Wesson. Estimated round count likely exceeds 8000.

Anyone else experience this???

[Mescalero]

Wow!
What powder?

[horsesoldier03]

I would gauge the cylinder gap and see how much gap is between the cylinder and the forcing cone. I think the correct term for this is checking the end shake. I think for a Smith the max tolerance is around .007, but, I am no gunsmith.

[Mescalero]

Joe has done the end shake thing on his Model 25.
Maybe he will grace us with a tutorial.
I remember reading how to do it.
That gun has other issues.

[Buck Elliott]

"Spitting gas" is usually more of a timing issue, in my experience..

[Old Savage]

This one has 6,000 rds through it



What I have noticed is that the crane has a bit of play in it. You can see in this picture that there is a slight edge to the fit at the front where the crane protrudes forward. This can be pushed back to flush. I think that is what end shake refers to.

[BigSky56]

Thats 2, for the timing needing adjustment. danny

[Gunnin'Wreck]

My vote would go for it being a timing issue as well. Is it spitting just gas or are there particles of either powder or bullet coming out as well? An easy way to tell would be to hold a piece of plain white paper up close to the side of the gun, fire a round, and see what hits the paper. If it is strictly gas you may just have an oversized cylinder gap. If it shows bullet shavings, you almost certainly have a timing problem.

I would be surprised if you have an erosion problem with only 8000 rounds through your revolver. I have two S&W handguns (a M57 and a M686) that have several times that many rounds through them and don't have an erosion problem, which also makes me think you have a timing issue.

[Chuck 100 yd]

I agree with Buck on timing and that is the first thing to check.
End shake is movement (endwise)of the cylinder, cylinder barrel gap will be measured with the cylinder all the way back. If there is too much end play in the cylinder you have (usually) too much headspace.
End shake and cylinder/barrel gap are related but not the same thing.

[J Miller]

Timing has little to do with forcing cone erosion. The OP's gun might have excessive barrel/cylinder gap and probably excessive end shake as well but it's not out of time. Were it out of time the erosion would be off center to the bore. Most of the erosion is caused by unburned powder being blown out of the B/C gap under extreme pressure. Ball powders are far worse for erosion than most flake or extruded powders.

After close to 8000 rounds my Mdl 28 was worse than that and was spitting badly. I dropped it off at a gunsmith in Phx and had the barrel set back a turn and the forcing cone recut. That fixed that problem.

That revolver has needed retimed and tuned about every 3500 rounds. N frame Smiths, at least the older ones, were prone to end shake problems. And end shake begets end shake. Once it starts it will beat itself looser and looser.

I've pretty much retired both my N frames. They only occasionally get shot. Just enough to make sure they still work.

Joe

[Mescalero]

Told you he'd be around.
That is why I asked what powder.
Joe is right, that stuff that rises to the peak of the pressure curve too quick; is ---- on metal.
Flame cutting is flame cutting.

[PaperPatch]

I forgot to mention that this one is a .41 Mag. Thinking about it...I likely put 2000 rounds thru it the first summer I had it.

The powder I burned most in this is Blue Dot. It was different from all other powders in that, upon firing...the burst of color that emerged from the cylinder gap resembled the blue flame of a properly tuned oxy-acetylene torch. With it, Sierra 170 grain JHC accurately scooted along at very high velocities...the muzzle report I recall is one that bystanders found uncomfortable.

Another favorite is the Speer 220 grain half-jacketed SWC. Accuracy at 100 yards with it was astonishing...and it sure packed a lot of spank!

Many other powders worked well. The only powder I quit using was IMR 4227. Though accuracy was sufficient...kernels of spent powder would accumulate beneath the ejection star, and caused binding during reloading.

I don't shoot it much anymore, and find milder guns to be more useful. It's a keeper though, and I'll let the folks at S&W repair it.

[Mescalero]

It will be worth it.
It will be like new when it comes back.i

[Bullard4075]

" Ball powders are far worse for erosion than most flake or extruded powders."
Curious.
Opposite of what (I thought) I've read and believed.
Thought Ball powders was one of the saviors of the poodle shooter problems in the past
Vietnam adventure. Cooler burning ball powers should reduce erosion.
Would someone amplify on this.
The more I learn the more I find I don't know or ........ know wrong.

[J Miller]

" Ball powders are far worse for erosion than most flake or extruded powders."
Curious.
Opposite of what (I thought) I've read and believed.
Thought Ball powders was one of the saviors of the poodle shooter problems in the past
Vietnam adventure. Cooler burning ball powers should reduce erosion.
Would someone amplify on this.
The more I learn the more I find I don't know or ........ know wrong.

Bullard,

What you are saying about ball powders is true ... in rifles.
But in revolvers if the powder pressures peak at the barrel cylinder gap you get super heated flame, ( IE the Blue Dots brilliant fire balls from PaperPatch's 41 mag. Add the hard balls of ball powder to that and the flame cutting become erosion as seen in the pics. In effect it's like a cutting torch mixed with a sand blaster all in one.
I used to shoot Winchester 540 ball powder in my .357s. Within 3000 rounds I'd have erosion so bad the gun was painful for anyone near by and sometimes me as well due to spitting caused by forcing cone erosion.
I switched to 2400 and the erosion all but stopped. Others at Handloads.com have reported no erosion after thousands of rounds of full house magnums using IMR 4756 ( I'm quoting from memory here, I "might" be off a number. )
So some powders do cause flame cutting erosion, and some don't. The type of loads and bullets used with different powders also contribute to erosion too.
The interesting thing is, forcing cone erosion is mostly evident with high pressure magnum revolver cartridges. My S&W 25-5 with over 8,000 rounds through it has none at all.

Joe

[Gunnin'Wreck]

" Ball powders are far worse for erosion than most flake or extruded powders."
Curious.
Opposite of what (I thought) I've read and believed.
Thought Ball powders was one of the saviors of the poodle shooter problems in the past
Vietnam adventure. Cooler burning ball powers should reduce erosion.
Would someone amplify on this.
The more I learn the more I find I don't know or ........ know wrong.

Bullard,

What you are saying about ball powders is true ... in rifles.
But in revolvers if the powder pressures peak at the barrel cylinder gap you get super heated flame, ( IE the Blue Dots brilliant fire balls from PaperPatch's 41 mag. Add the hard balls of ball powder to that and the flame cutting become erosion as seen in the pics. In effect it's like a cutting torch mixed with a sand blaster all in one.
I used to shoot Winchester 540 ball powder in my .357s. Within 3000 rounds I'd have erosion so bad the gun was painful for anyone near by and sometimes me as well due to spitting caused by forcing cone erosion.
I switched to 2400 and the erosion all but stopped. Others at Handloads.com have reported no erosion after thousands of rounds of full house magnums using IMR 4756 ( I'm quoting from memory here, I "might" be off a number. )
So some powders do cause flame cutting erosion, and some don't. The type of loads and bullets used with different powders also contribute to erosion too.
The interesting thing is, forcing cone erosion is mostly evident with high pressure magnum revolver cartridges. My S&W 25-5 with over 8,000 rounds through it has none at all.

Joe

This a really enlightening thread for me. I bought a M57 - 41 mag. in 1970. I have no accurate way of counting the rounds I have through it, but suffice it to say that an average of 1000 rounds a year would be conservative. Probably 75 or 80% of those loads were mid-range loads utilizing Unigue. The remainder were full throttle loads using 2400 or H110. I don't have an erosion problem yet. It would seem that the type of powder might have a lot to do with it. The only ball powder I ever used was 630-P, and I used very little of it due to inconsistency in pressure signs.