Weird Half Moon Mark on recoil Shield of 66 No Dash

Homerboy · January 3, 2012, 07:35 AM

Gun is in fine shape. Locks up tight and no front to back movement in the cylinder. But it has this mark around the firing pin hole that is a perfect matcg to a shell casing. it's etched into the metal, not dirt. Any ideas? Gun fired fine yesterday with 158 grain .357 and .38's.

Double Naught Spy · January 3, 2012, 09:28 AM

Cylinder slightly misaligned with barrel?

You can get better closeup pics by moving the camera back slightly so that the marks are at a distance where the camera can focus. Then you can magnify the image to make the impacted area larger or simply crop the image and resize.

Scorch · January 3, 2012, 01:17 PM

Quote:

it has this mark around the firing pin hole that is a perfect matcg to a shell casing

Yep, it is a perfect match for a casing because that is what causes that mark. When you fire a cartridge, the case recoils backwards against the recoil shield as the bullet travels down the bore (that's why it is called the recoil shield). It's that whole Newton's 3rd Law of Motion thing, equal and opposite, you know. The case peens and burnishes the steel on the recoil shield. It's normal, it's entirely safe, it is predictable, and we smiths actually use that wear to tell if a revolver has ever been fired and how much (in relative terms).

Double Naught Spy · January 3, 2012, 04:05 PM

Um yeah, Scorch, I think he understands that it was caused by the impression of the case. Why is it a half moon and not a full moon? What does Newton's law say about imbalanced impressions/depressions?

Scorch · January 3, 2012, 07:15 PM

Newton's Laws don't say anything about ammo loaded out of round and not totaly square to anything. That's for shooters to post about because they don't get it.

Roughedge · January 3, 2012, 08:52 PM

I just checked my 686 that has a few thousand round through it and it has a round stain but nothing like the one in the picture. have you shot some hot loads in it?

johnwilliamson062 · January 3, 2012, 09:33 PM

I like 00Spy's explanation. None of my revolvers have markings anywhere close to that deep.

Homerboy · January 3, 2012, 10:00 PM

Roughedge, I have fired exactly 50 rounds of .38 and 6 158 grain .357. Just got the gun. I'm finding it hard to believe it was shot with super hot loads because the forcing cone is not cracked and the gun is tight. No wiggle front to back or side to side on the cylinder.

jmorris · January 3, 2012, 11:18 PM

Post a photo of the fired case heads.

nogo · January 3, 2012, 11:54 PM

Firing pin has peened hole in firing pin bushing. Clean it up with a stone. Over the years I've seen this on numerous law enforcement ranges. I wouldn't worry about..but if you do, S&W can replace bushing, which would be knocked out, and a new one swaged in.

Homerboy · January 4, 2012, 07:37 AM

Quote:

Firing pin has peened hole in firing pin bushing. Clean it up with a stone. Over the years I've seen this on numerous law enforcement ranges. I wouldn't worry about..but if you do, S&W can replace bushing, which would be knocked out, and a new one swaged in.

You can see that in the pic?

Homerboy · January 4, 2012, 07:45 AM

I'll have to do that next time I shoot it. The cases are in the bin with all my other .38 brass. I have no idea which were fired by this particular gun.

gyvel · January 4, 2012, 08:28 AM

My uneducated guess would be gas erosion from leakage around a case that isn't expanding completely,

Homerboy · January 15, 2012, 07:20 PM

**Update** Just got off the phone with a S&W authorized repair center. They believe it's a tool mark. Gun fired and functioned fine. Timing and endshake are all good. The guy even remarked how the gun looks new, which it does, despite being nearly 40 years old. Guess someone fell asleep at the switch the day it was made. No matter. Gun is still sweet. Looking forward to getting it back.

James K · January 15, 2012, 11:42 PM

Looks like I was wrong, but so were the "erosion" and "super hot loads" ideas.

Jim

January 3, 2012, 07:35 AM	#1
Homerboy Junior member Join Date: June 16, 2004 Location: Pennsylvania Posts: 1,320	Weird Half Moon Mark on recoil Shield of 66 No Dash Gun is in fine shape. Locks up tight and no front to back movement in the cylinder. But it has this mark around the firing pin hole that is a perfect matcg to a shell casing. it's etched into the metal, not dirt. Any ideas? Gun fired fine yesterday with 158 grain .357 and .38's.

January 3, 2012, 09:28 AM	#2
Double Naught Spy Senior Member Join Date: January 8, 2001 Location: Forestburg, Montague Cnty, TX Posts: 12,793	Cylinder slightly misaligned with barrel? You can get better closeup pics by moving the camera back slightly so that the marks are at a distance where the camera can focus. Then you can magnify the image to make the impacted area larger or simply crop the image and resize. __________________ "If you look through your scope and see your shoe, aim higher." -- said to me by my 11 year old daughter before going out for hogs 8/13/2011 My Hunting Videos https://www.youtube.com/user/HornHillRange

January 3, 2012, 04:05 PM	#4
Double Naught Spy Senior Member Join Date: January 8, 2001 Location: Forestburg, Montague Cnty, TX Posts: 12,793	Um yeah, Scorch, I think he understands that it was caused by the impression of the case. Why is it a half moon and not a full moon? What does Newton's law say about imbalanced impressions/depressions? __________________ "If you look through your scope and see your shoe, aim higher." -- said to me by my 11 year old daughter before going out for hogs 8/13/2011 My Hunting Videos https://www.youtube.com/user/HornHillRange

January 3, 2012, 07:15 PM	#5
Scorch Senior Member Join Date: February 13, 2006 Location: Washington state Posts: 15,249	Newton's Laws don't say anything about ammo loaded out of round and not totaly square to anything. That's for shooters to post about because they don't get it. __________________ Never try to educate someone who resists knowledge at all costs. But what do I know? Summit Arms Services

January 3, 2012, 08:52 PM	#6
Roughedge Senior Member Join Date: January 24, 2011 Location: Monroe,NC Posts: 669	I just checked my 686 that has a few thousand round through it and it has a round stain but nothing like the one in the picture. have you shot some hot loads in it? __________________ The man that die's with the most stuff win's!

January 3, 2012, 09:33 PM	#7
johnwilliamson062 Junior member Join Date: May 16, 2008 Posts: 9,994	I like 00Spy's explanation. None of my revolvers have markings anywhere close to that deep.

January 3, 2012, 10:00 PM	#8
Homerboy Junior member Join Date: June 16, 2004 Location: Pennsylvania Posts: 1,320	Roughedge, I have fired exactly 50 rounds of .38 and 6 158 grain .357. Just got the gun. I'm finding it hard to believe it was shot with super hot loads because the forcing cone is not cracked and the gun is tight. No wiggle front to back or side to side on the cylinder.

January 3, 2012, 11:18 PM	#9
jmorris Senior Member Join Date: November 22, 2006 Posts: 3,078	Post a photo of the fired case heads.

January 3, 2012, 11:54 PM	#10
nogo Senior Member Join Date: September 7, 2009 Location: central texas Posts: 215	Firing pin has peened hole in firing pin bushing. Clean it up with a stone. Over the years I've seen this on numerous law enforcement ranges. I wouldn't worry about..but if you do, S&W can replace bushing, which would be knocked out, and a new one swaged in.

January 4, 2012, 07:45 AM	#12
Homerboy Junior member Join Date: June 16, 2004 Location: Pennsylvania Posts: 1,320	I'll have to do that next time I shoot it. The cases are in the bin with all my other .38 brass. I have no idea which were fired by this particular gun.

January 4, 2012, 08:28 AM	#13
gyvel Senior Member Join Date: August 30, 2009 Location: Northern AZ Posts: 7,172	My uneducated guess would be gas erosion from leakage around a case that isn't expanding completely,

January 15, 2012, 07:20 PM	#14
Homerboy Junior member Join Date: June 16, 2004 Location: Pennsylvania Posts: 1,320	Update Just got off the phone with a S&W authorized repair center. They believe it's a tool mark. Gun fired and functioned fine. Timing and endshake are all good. The guy even remarked how the gun looks new, which it does, despite being nearly 40 years old. Guess someone fell asleep at the switch the day it was made. No matter. Gun is still sweet. Looking forward to getting it back.

January 15, 2012, 11:42 PM	#15
James K Member In Memoriam Join Date: March 17, 1999 Posts: 24,383	Looks like I was wrong, but so were the "erosion" and "super hot loads" ideas. Jim