Slugging a 5- or 3-groove barrel

[noylj]

Got the May-June American Handgunner and Mike Ventorino mentions using a v-block to determine the "diameter" of a slug run through a 5-groove barrel.
Now, I am the first to admit that I am not a machinist and have no idea how universal such a block would be, but it just seems, mentally, that the angle of the block would need to "exactly" match the angle of the grooves being measured.
I know that there are v-angle micrometers, but again, the angle would need to match the grooves, such that a single block or micrometer would only be applicable to a specific number of grooves and may also need to be matched to a small range of diameters.
Does anyone know: is there a universal block that would work from 0.220-0.500" and both 3- and 5- groove barrels? I see the micrometers as ringing in the $900+ range, so see a block or two as a better, affordable alternative.

[grouch]

I've always wondered why it wouldn't work to push an approriately sised bullet nose into the muzzle and measure the diameter where the lands/grooves just touch.
Grouch

[goofyoldfart]

just a thought--- take your bullet and some ,001 or .002 shim/feeler stock, wrap tightly around the bullet and measure with an inexpensive Mike. total dimensions minus 2X the thickness of the wrap material equals the groove depth. God Bless to all.

[303Guy]

I've always wondered why it wouldn't work to push an approriately sised bullet nose into the muzzle and measure the diameter where the lands/grooves just touch.That's exactly what I do. I confirmed the correctness with a turned brass rod. Measuring the grooves is something else again.

I also used a boolit the just about fit the bore and pushed it in with a cup nose brass rod that stopped it from turning and was able to get a good measurement. Pushing it all the way through allowed me to measure the narrowest portion of the bore too. Too soft a boolit doesn't work.

One could, by using a slight tapered boolit, push it into the breach until it has started to engrave the rifling then remove it and measure the diameter at the point were the boolit has fully engaged the grooves on another identical boolit. Bear in mind that deformation could skew the results.

[ku4hx]

I see the micrometers as ringing in the $900+ range, so see a block or two as a better, affordable alternative.

Back when I got mine they were waaaay less costly than that. But before I got one, or even slugged a bore for that matter, I bought a number of sizing dies for my Lyman 450: .355", .356", .357", .358", .359" and .360". At the time my interest was 38 Spcl, 357 Magnum and 9mm.

The purchase of those six dies did two things: allowed me to very cheaply "dial-in" by experimentation the optimum diameter for each gun and I got more toys. A short while later I did the same with 45 ACP and 44 Magnum.

Dies back then were $5 each and over the years this $60 or so turned out to some of the best hand loading money I ever spent. At $900 today, I'd still think buying several dies and experimenting would be far cheaper and you get to claim the need to experiment if you need that.

[10x]

The v block method works well. You can build one from a small block of aluminum using a file if you are careful. you calibrate it with a 30 caliber bullet to discover how much the block adds, then when you measure the slug from the bore using the block you subtract the difference from the block. So long as the rifling rests on the flats of the block you are good to go.
You just have to ensure that the block itself is true and that isn't too hard. to do.

A $10.00 micrometer from Harbour Freight will get you into the ballpark as well.

[Reload3006]

Got the May-June American Handgunner and Mike Ventorino mentions using a v-block to determine the "diameter" of a slug run through a 5-groove barrel.
Now, I am the first to admit that I am not a machinist and have no idea how universal such a block would be, but it just seems, mentally, that the angle of the block would need to "exactly" match the angle of the grooves being measured.
I know that there are v-angle micrometers, but again, the angle would need to match the grooves, such that a single block or micrometer would only be applicable to a specific number of grooves and may also need to be matched to a small range of diameters.
Does anyone know: is there a universal block that would work from 0.220-0.500" and both 3- and 5- groove barrels? I see the micrometers as ringing in the $900+ range, so see a block or two as a better, affordable alternative.

I am a machinist-Tool n Die maker now I am working in a calibration laboratory. V anvil micrometers and V blocks measure Diameter and they are very accurate. The angle is not as important as you may think because it measures from 3 points not 2 which will allow the odd number of rifling to work. Using a V block and a plunger type of Dial indicator on a surface gauge if you have a rod of known diameter you can very accurately measure the diameter of any bullet by simply adding the indicator reading to the known size of rod .. or subtract as the case may be.

[yovinny]

This guy has both the 60* & 108* V mikes for under a C note.
Chinese made and in thousands, not tenths, but none the less a decent deal for what it is.
http://cdcotools.com/

I have one I bought probably 10 years ago and it's not a bad piece of kit, though I've never had to use it for measuring a bullet, just grinding endmills and such.

Cheers, YV

[Pepe Ray]

Heads up yall.
The "V" block for a 5 L&G slug must be a 108* V.
They are available from your own 45Nut
The formula for calculating the measured result is stamped in the block
for your convenience. Reasonably priced.
SUPPORT YOUR TEAM
Pepe Ray

[Canuck Bob]

I carefuly measured the point on the throat slug were the taper shows evidence on the rifling. It isn't dead accurate but should be quite close.