Barrel dots/dimples explained...

[Forrest Halley]

So years ago I knew all about this, but time passed and I have forgotten. What is the significance of the dot system on the bottom of the barrels? More specifically what is the difference between a one dot and a two dot. I recently acquired a one dot and have not fired it yet, but have been quite happy with my two dot which seems to favor the the 147 grain bullets. Is the one dot going to be looking to shoot lighter weight projectiles? 

 

Thank you for the wisdom. 

[Forrest Halley]

[gnappi]

AFAIK there is no dot "system", what I "think" you may  be  referring to may be hardness testing punches? 

 

There was a Star and or a dot system on shotgun barrels to indicate the choke / constriction, but I know of none on any other firearms. 

Edited April 12, 2022 by gnappi

[P Taylor]

I have read on slides it is a way to mark which machine the parts come from for QA tracking if there is a problem. No idea if it is the same on barrels.

[gnappi]

Being literally raised in a machine shop, dimples are the QC dept way of assuring it passes the Brinell test for hardness. Two dimples usually means the manufacturer AND the client who ordered the part (or subbed it out) tested it. Now if there were three (I really doubt it on a commercial part) dimples, I'd suspect the third was military, four? Not a way I can see logical. A "system" of two levels (or more) of "quality" makes no sense. They either pass or not. 

 

 

 

 

[SteelCityShooter]

Both my  5" M&P9 2.0 and 4" Compact 2.0 have one dot on the barrel hood and I assume they are QC hardness test mark.  I can't believe any volume manufacturer could afford the time and expense to determining which bullet weight is more accurate in every barrel.   That explanation makes no sense.

[Johnny_Chimpo]

On 4/1/2022 at 10:03 AM, Forrest Halley said:

So years ago I knew all about this, but time passed and I have forgotten. What is the significance of the dot system on the bottom of the barrels? More specifically what is the difference between a one dot and a two dot. I recently acquired a one dot and have not fired it yet, but have been quite happy with my two dot which seems to favor the the 147 grain bullets. Is the one dot going to be looking to shoot lighter weight projectiles? 

 

Thank you for the wisdom. 

 

They are marks from the hardness tester, an inspection step to confirm one of the qualities of the heat treatment process.  They have absolutely nothing to do with what bullet a barrel will like.

[ryan45kim]

This is what I’ve been told.

 

the original barrels were 1/16 twist and do not have dots.

when s&w went to a 1/10 twist they began marking the barrels with dots.

there are one dot and two dot barrels, they indicate which machine the barrel was made on. 
 

 

[Jhp147]

I took a tour of the S&W plant in 2007.  The guy doing the tour was a 30 year employee of the factory, doing this as a volunteer.  While showing us where they were shaping or cutting M&P barrels, he mentioned some dots or maybe dimples on the bottom of the barrels or chambers as though he got asked about them often.  He said they were not any kind of secret code, they were a way of measuring tool wear.  I guess these are the dots you mean, but I’m not sure.  Then again, that was 15 years ago.

Edited May 2, 2022 by Jhp147