How do you determine bore diameter in a 5 groove barrel?

[woody2]

Just tried to slug the barrel on my new S&W 9mm and discovered that it is a 5 groove barrel. How the heck do I determine the correct diameter to size boolits?

[292]

You can wrap a thin feeler gauge around the slug, measure and then deduct twice the thickness of the feeler gauge. I just measure at the widest point, which is slightly larger than groove diameter and size .001" over that. The second method has worked for me on 2 Smith handguns. Is your gun a M&P?

[woody2]

Thanks, 292, using your second method I'm getting about .3553. I have .356 and .358 dies so I'll try the .356 first. The gun is a 1911.

[woody2]

Just tried the first method using some .003 shim stock and got measurements of .357 to .358, including the shim stock. This indicates the bore is in the .351 to .352 range. Not real close to the other method that indicated about .355. Is this a normal variation? If the .351 is correct will shooting a .356 bullet be a problem?

[captaint]

woody - Based on my limited experience with the 9mm, the .356 die may well be too small. Check to be sure the .358 sized boolit will chamber OK, then go shoot some. I size mine at .358. enjoy Mike

[292]

Just tried the first method using some .003 shim stock and got measurements of .357 to .358, including the shim stock. This indicates the bore is in the .351 to .352 range. Not real close to the other method that indicated about .355. Is this a normal variation? If the .351 is correct will shooting a .356 bullet be a problem?

I would say that is not a normal variation. When I used the 2 methods I came up with closer measurements. I use a .356" Lee push through with gives me .35675" boolits. They work in my M&P.

[buyobuyo]

Here's another recent thread covering the same topic: http://castboolits.gunloads.com/showthread.php?t=169178

[Artful]

http://www.practicalmachinist.com/vb/attachments/f24/15820d1253910083-measuring-5-groove-slugs-100_1848_crop.jpg

[gofastman]

woody - Based on my limited experience with the 9mm, the .356 die may well be too small. Check to be sure the .358 sized boolit will chamber OK, then go shoot some. I size mine at .358. enjoy Mike

yep, my 9mm barrel is .357" (Taurus 709)
I size to 358"

[Jbar4Ranch]

Buy a V anvil micrometer.

[Pepe Ray]

artfull;
A mis type perhaps?
The included angle is 108* not 180*
The V block mikes are WAY too expensive for most ordinary casters.
Get the "V" block guage from Ken. (45 Nut)
Pepe Ray