What is it with S&W...

[Matt_G]

...and their need for cutting barrels with an odd number of grooves!?
<insert long string of expletives here>

All I want to do is slug the barrel to see what I've got.
But Noooooo, we use 5 grooves so you have to have a special mic or play f*** f*** with it.
Grrrr

Sorry, I just needed to get that off my chest.

 

[Petrol & Powder]

There are solutions to measuring a slug with an odd number of lands/grooves, but I'm sure you already know that.
I suspect the needs of people measuring their barrel groove diameter AFTER the gun left the factory was NOT a major concern of the folks at S&W.

 

[Bret4207]

Measuring Groove Diameters of Odd Groove Bores

Details of several techniques to measure the groove diameters of firearms with odd groove bores.

www.texas-mac.com

 

[Matt_G]

Thanks Bret.
That's an interesting read.

 

[Mainiac]

Smith has always been 5 groove,as far as i know,wonder why?
Some old guy must have had a reason,and why change threw the years,,

 

[Dusty Bannister]

It would seem it maybe something related to the width of the lands and grooves with wide grooves providing better grip in these calibers. The two groove military rifle barrels were cost cutting and to expedite production.

 

[popper]

Faxton info kinda makes sense but their words are not clear. Even grooves on opposite sides makes the dia of the bullet there SMALLER and weaker! Any uneven stresses could bend the bullet. Long time ago I did a twist test on a RD 180gr. Always broke the bullet at the grease groove - every time.

 

[StrawHat]

Not all S&W revolvers are 5 groove. The Model 1917 and subsequent ACP revolvers were 6 groove As specified by the Army for the 1917. I believe they stayed with the Army rifling until the late 20th or early 21st century.

Kevin

 

[Petrol & Powder]

Or….probably,…. far more likely………they (S&W) picked 5 grooves early on for some long forgotten reason (it was compatible with the machinery they had, the math worked out conveniently, the machinist liked 5 grooves…..) and that is what they used!



Often these explanations are NOT complicated.

 

[RicinYakima]

FWIW, you made me curious, so I checked my 1989 625-3, 45 ACP, just now. Five groove rifling in that one.

 

[JonB]

my 625 JM has 6 grooves.

View attachment 8355

 

[JonB]

When I've felt the need to measure a lead slug from 5 groove barrel, I wrap a strip of 0.0045" popcan metal around the slug, keep a firm grip on that strip with a pliers, measure with a Mic, then subtract 0.009" and I get a close enough measurement.

 

[Ian]

Groove diameter in a revolver is a useless statistic anyway, never needed it. Size your bullets to the throat diameter, check for thread choke with a flashlight or pin gauges, and if the barrel doesn't lead then the groove diameter is small enough.

I have a few S&W revolvers and don't like any of them, never saw what all the worship and hoopla was about. Flame on. Shot a Colt Police Positive once, now THAT was a nice revolver.

 

[fiver]

i like my little 625 also.
the 629's etc. all got moved along shortly after messing with them for a week or two.
i was super reluctant to buy that 625 too but i really wanted a 45 acp/rim revolver, it's good with some minor disappointment attached, but no real complaints.

 

[Matt_G]

Well, I got that SD40 VE barrel measured thanks to the link @Bret4207 posted.
I used the very last method in that article and it worked just fine.

I really should build a Tri-Rod gauge as described in that article.
Lord knows there are enough barrels here with 5 grooves to justify it.

Of course, the "spin the slug" method works as well but you can't be sure of your number really.
When doing that, if you just add .001 to whatever number you get, you're probably pretty close, assuming you have a decent slug to work with.
I'm picky though and would like a more "trustworthy" number.

<Shrug> Another first world problem...

 

[Petrol & Powder]

First World Problem Indeed.

 

[StrawHat]

I just looked at some of mine. All my 1917s are six groove as are my Model 1950s, and my Model 25-2s. The Model 22-4s that I have are 5 groove.

But, I size to the largest throat on the shooters and load them all with that. I do NOT find a specific load for each revolver. If a revolver won’t shoot with one of my preferred loads, it goes down the road.

Kevin

 

[Petrol & Powder]

I think the OP is referring to a pistol and not a revolver.

But just in general concerning revolvers – YES, the throats of a revolver cylinder are the critical factor in that system. On a revolver cylinder, the throat at the forward end of the chamber is the last sizing die the bullet will go through before reaching the barrel.

When dealing with revolvers there is no sense in sizing the bullet larger than the throat diameter because the bullet will be “sized” by the throat before it reaches the barrel. And there is nothing to be gained by sizing the bullet smaller than the throat, unless you just like poor accuracy, lost velocity, and removing leading from barrels.

In a perfect world………the throat diameter will be slightly larger than the grove diameter of the barrel in front of the cylinder. In that situation, the best practice is to size the bullet to match the throat.

NOW, getting back to the OP, who I believe is inquiring about a pistol barrel with a 40 S&W chamber, he has a different set of parameters.

First, the cartridge must reliably feed into the chamber. Because the 40 S&W headspaces on case mouth, the “throat” is effectively the area just in front of the chamber before the rifling begins. The amount of space here determines how big the bullet can be in both diameter and length beyond the casing.

Second, the bullet must fit the barrel (which is why he is concerned about groove diameter).

Here the criteria are a bit simpler. The bullet needs to be fat enough to fit the barrel but not too fat to go down the barrel.

Fortunately, when dealing with pistol chambers that are integral to the barrel (as opposed to revolver chambers) you only have ONE chamber to deal with.

For a pistol barrel (not a revolver barrel), a bullet seated in a casing that will reliably enter the chamber and that is slightly larger in diameter than the groove diameter, is all that is needed. 40 S&W chambers/barrels are fairly consistent. The SAAMI specifications for a 40 S&W barrel are a bore diameter of .390” and a GROOVE diameter of .4005”. So, a cast lead bullet sized to .401” that will reliably chamber, is probably going to work.

 

[Dusty Bannister]

I would add that the height and width of the lands can make a difference as well. The Glock rifling is a bit different from cut rifling and in my experience the .401" did allow a bit of leading with bullets from a relatively hard alloy. By applying a light coating of Tumble lube, the diameter was increased just enough to seal the bore and leading stopped. Enlarging the bullet size die as little as .0005" resolved the issue in the barrel of my Glock but may not work for others.

 

[Mainiac]

Not all S&W revolvers are 5 groove. The Model 1917 and subsequent ACP revolvers were 6 groove As specified by the Army for the 1917. I believe they stayed with the Army rifling until the late 20th or early 21st century.

Kevin

Didnt know this,thanks!