S&W 5 groove: measuring diameter

[Jumping Frog]

Well, I finally bought a real sizer instead of using the Lee tumble lube approach.

Need to order a sizing die for my S&W 629 (.44 Mag), so I figured I'd check the dimensions.

The 6 chambers were easy. I slugged those all between 0.4289" and 0.4292", and was happy to see all six were within 3 ten-thousands of an inch.

After driving a slug through the barrel, I can't figure out how to get a decent measurement for my bore size. With the 5 lands & grooves configuration, trying to measure the diameter is a problem. When there is a raised spot on the bullet where the groove is, the opposite side of the bullet (180 degrees) is a recessed pot on the bullet where the land is.

Now, I am not going to go buy some fancy $150 measuring fixture just to satisfy my curiosity. But does anyone know of a simple approach that will give a decent answer?


Footnote: I assume since the chambers are all around 0.429, I should try buying a 0.430" sizing die, right?

[captaint]

Froggy - You need to find a thin piece of metal to wrap around the slug. It will need to be thicker than, like, aluminum foil. So, wrap it around, carefully measure with mic's and subtract the thickness of the metal wrap twice - once for each side measured. OK ??? Let us know how you make out. enjoy Mike

[EdS]

I had the same problem, but tried the following: I tried dropping the slug from the barrel through the cylinder throats of several revolvers until I found one where the slug passed through with a little resistance. The diameter of this throat should be just slightly larger than the barrel's groove diameter. -Ed

[JonB_in_Glencoe]

Froggy - You need to find a thin piece of metal to wrap around the slug. It will need to be thicker than, like, aluminum foil. So, wrap it around, carefully measure with mic's and subtract the thickness of the metal wrap twice - once for each side measured. OK ??? Let us know how you make out. enjoy Mike

Yep, I do it this way. Using popcan aluminum.

[wkelley70]

I had the same question about how to measure my 5-groove M&P 40. Here is the link to a nice write-up on the CMP forum: http://forums.thecmp.org/showthread.php?t=3255.

[buyobuyo]

Here is the method that legi0n posted on how to measure a 5 groove slug. It requires a little math, but it is all covered in the thread.

http://castboolits.gunloads.com/showthread.php?t=119952

[H.Callahan]

Try using a thin, flat feeler gauge as the wrap-around. You will then be able to just subtract 2x the thickness of the gauge from your micrometer measurement to find the slug diameter.

[Jumping Frog]

Well, I found a piece of metal shim stock 0.0041" thick, wrapped it around the bullet, and measured it 4 times at various orientations around the bullet with my micrometer.

I come up with a 0.426" diameter. Seems smaller than it should be. Perhaps the barrel is "squeezed" at some point, like where it is screwed into the frame.

Is this something I should be concerned about?

[captaint]

Froggy - Did you notice any extra resistance when the slug got to the "frame" portion of the barrel ?? If so, you probably do have some "thread choke". This will size the boolit smaller for the rest of the journey down the barrel - thus - leading. enjoy MIke

[Jumping Frog]

I am going to re-slug the barrel, being sensitive to any change in resistance.

[10x]

Here is the method that legi0n posted on how to measure a 5 groove slug. It requires a little math, but it is all covered in the thread.

http://castboolits.gunloads.com/showthread.php?t=119952

a home made V block
neat!
I learn something new every day.

[Pepe Ray]

Ken (45Nut) has had the "V" blocks for sale for a long time.
I keep posting a reminder whenever this comes up but the gang all seem to be bent
on fumbeling a metal wrapped boolet/slug between the mike jaws. Oh well---

Sorry Ken.
Pepe Ray

[10x]

Ken (45Nut) has had the "V" blocks for sale for a long time.
I keep posting a reminder whenever this comes up but the gang all seem to be bent
on fumbeling a metal wrapped boolet/slug between the mike jaws. Oh well---

Sorry Ken.
Pepe Ray

Link to the V blocks for sale please?

[Pepe Ray]

No LINK
Just P.M. Ken. ie. 45 Nut
Pepe Ray

[45nut]

I have 4 left available here.

[Jumping Frog]

Have a v-block on the way to my house! Ya-hoo, more tools.

[Jumping Frog]

Ken (45Nut) has had the "V" blocks for sale for a long time.
I keep posting a reminder whenever this comes up but the gang all seem to be bent
on fumbeling a metal wrapped boolet/slug between the mike jaws. Oh well---

Sorry Ken.
Pepe Ray
Glad you mentioned this, as I followed up and purchased the v-block from Ken (45Nut).

Big difference!

I was using metal shim that was 0.0041 inch thick, wrapping it around the bullet as suggested. As noted above, I measured it as 0.426 inches, but I never felt like it was a good measurement.

Once I got the v-block, I measured two different slugs, using the average of all 5 groove diameters. Using the simple v-block formula, both slugs measured out at 0.429 inches, within two ten-thousandths of each other.

I believe the act of measuring the diameter with the shim stock pressed some of the stock into the corresponding bullet land and gave distorted measurements.

Now I've got a number of other barrels to measure!