Weird Half Moon MArk on Model 66 recoil Shield

[Homerboy]

Just got a 66 no dash. Gun is very clean and tight. On the recoil shield, right above the firing pin hole, there is a half moon that is etched into the metal. It perfectly follows the existing faint mark caused by the cases coming back on firing. Gun functions fine, but I've never seen anything like it with it being actually eteched into the metal. Anyone ever see anything like this or have any opinions?

 

[Jim K]

It is the recoil shield, a semi-permanently assembled part of the frame. S&W uses it to take the shock of recoil of the cartridge case. If it is battered, it can be replaced (by the factory) without scrapping the frame. Most of the time, the fitting is so precise that its presence can't be detected, but perfection eludes us all and that one can be seen.

Jim

 

[357 Terms]

You say "ethched" can you feel it when you run a finger accross it?

That is a lil strange.

 

[Homerboy]

It's very shallow, but it is etched into the metal. Follows the exact shape of a casing.

 

[RevolvingGarbage]

It is the recoil shield, a semi-permanently assembled part of the frame.

Doesn't seem like that's what the OP is talking about.

If it is what it looks like, then someone touched off a very hot loaded round in that gun, probably one that had a thinner than normal rim (giving it more room to rebound).

*EDIT*

It could also possibly be from a round that had a case rupture during firing, causing the hot gasses to spill out of the back of the chamber, and etching or eroding the metal not covered by the rim of the case.

 

[Homerboy]

So does it make the gun unsafe to fire? it handled like a dream when I shot it the other day.

 

[357 Terms]

So does it make the gun unsafe to fire? it handled like a dream when I shot it the other day

As long as everything else checks out ok I would't worry about it.

 

[RaceM]

Yup, could be from a ruptured case. Had a CCI Blazer 357 round split on me once and it left a line down the inside of the chamber (really torqued me off cuz the gun was perfect up until then). Don't recall if there was enough blow-by to do the recoil shield though.

 

[Jim K]

OK, take a look at any other new S&W revolver and if you look carefully you will see that by some strange coincidence they were all fired with extra hot loads and had case ruptures.

S&W used to use a bushing that was only slightly bigger than the primer, but with their stainless steel and alloy frames they extended the hardened bushing to the size of the cartridge rim.

Jim

 

[rcmodel]

Clean it real good.

The hammer nose bushing on a Model 66 is the ring in the middle you can plainly see in the photo.

I have never seen a primer nose bushing as big as the cartridge rim on any S&W, stainless or otherwise, as it would hang over into the ratchet cut in the frame and take another milling operation to trim the bottom edge off after it was pressed in the finished frame.

The outside mark on your gun is crud or corrosion of some kind that I betcha will clean off if you try using a lead way cloth or a bronze bore brush & power solvent.

No case leak is going to flame cut the recoil shield like that, ever.

rc

 

[MutinousDoug]

What do the rims of your cases look like? That's where the wear on the recoil shield appears to be coming from, doesn't it?
Am I missing something?

Doug

 

[Homerboy]

RC, I cleaned the hell out of it, and now it looks like a clean half moon mark eteched into the metal.

Doug, I dumped the brass into a bucket filled with .38 brass, so I can't tell which ones were actually shot with this particular revolver. The cases all dumped out nice and smooth from the cylinders when I was reloading, though.

 

[rcmodel]

It could be a factory defect.

The recess for the hammer nose bushing is cut with a reamer through the barrel hole in the frame before the barrel is installed.

Perhaps it was Monday morning, and the reamer guy ran it in till the outside stop or a chip on the reamer marked the recoil shield.

That would be my best guess.

There is simply nothing going on at the outside edge of the cartridge rim that would cause that. Not leaking back around the case, not a split case, not a blown primer, nothing.

If the rim or case itself split or cracked, you could possibly get a carbon stain right at the split, but not halfway around the rim.

However, I do not believe a single case failure could possibly damage a recoil shield to that extent on a stainless steel revolver.
I also do not believe if 200 cases failed and gas cut the recoil shield, they would all fail only at 11:00 to 1:00 O'Clock in the chamber.

If a primer leaked, you would get etching on the HN bushing, not at the outside edge of the rim.

So, I think it is a factory defect that has been there since day one.

The only other possible explanation is, it is normal for powder residue to foul the recoil shield there.
Perhaps due to a odd set of circumstances involving no cleaning, humidity, etc, the recoil shield got some corrosion under the powder fouling.

However, that also seems far less likely then a Monday morning reamer slip-up when they made it.

rc

 

[briansmithwins]

Any flame cutting? Any chance this is just wear from the revolver being shot a whole bunch?

BSW

 

[F-111 John]

Put a spent casing in each cylinder, and check the gap between the back of the cartridge and the back of the frame. Check all six chambers.

You may find that the gap is smaller at the top than at the bottom of the round because the recoil face of the frame is not perfectly square with the rear of the cylinder. If so, then when a round is fired and the case recoils back into the frame, the top of the round hits first, and has peened a small groove in the recoil face.

All of my revolvers have a nearly full round mark just like your half moon mark, caused by case recoil.

I wouldn't worry about it, as the groove that has been created has probably evened out the recoil face, so now your rounds are hitting squarely on the recoil face.

 

[Remllez]

I think F-111John nailed it...it's a high spot that's taking the brunt of the recoil. As he said"all my revolvers show a case outline in that spot ", yours is only showing 1/2 because it's not square.

There shouldn't be any problem shooting that gun in regards to the outline on the recoil shield. In fact the more you shoot it the more pronounced that mark will become, it may end up with a full circular mark as the round count goes up.

 

[PabloJ]

Looks like artifact of mass production. I would have competent gunsmith look at it before further use.

 

[Jim K]

Gee, me and Rodney D. just don't get no respect! I tell you folks what it is, and everyone just ignores that and keeps talking about flame cutting and hot loads.

It is there on all the newer revolvers, including the 642 I have in my hand. In the picture, you can even see that it extends down into the ratchet clearance cut because it was installed before that cut was machined. Case head battering could not reach that part of the frame. Just look, darnit!

Jim

 

[evan price]

A guess- the hammer nose bushing hole was incorrect, so they reamed out the frame and built it back up and redrilled the HNB hole.

 

[Homerboy]

Jim, the 66 in question is a no dash model made in 1974. And that etching is nowhere on any revolver I currently own, or any I have ever owned (and I've had at least 15 revolvers pass through my safe over the years.) A light mark, yes. A half moon actually etched into the steel? Never seen it. And the etching itself only extends to parallel with the firing pin hole. It becomes a light mark, not an etching, after that. The gun locks up tight and shot like a dream, but it's off at S&W getting checked out. I bought it used and it otherwise looks almost new, so I'm thinking a factory goof when it was made.

 

[Remllez]

Sorry, I was looking at the mark around the firing pin. If that's not what your talking about then I can't see the mark you describe.

 

[Slamfire]

I hope it is not an example of peening.

If the headspace of the cartridge is too much a cartridge will peen the recoil shield. The case gets too much of a running start and hits the recoil shield too fast.

If the whole area is depressed, that could be it.

 

[Homerboy]

Sorry, I was looking at the mark around the firing pin. If that's not what your talking about then I can't see the mark you describe.

It's the big circle around the firing pin, but the etching is only half around. The bottom half is just a faint circle.

 

[Jim K]

Let us know what S&W says.

Jim

 

[F-111 John]

OP's picture with the recoil shield highlighted, and the half moon mark highlighted.