How to measure groove dia on 5 groove bore?

[63 Shiloh]

Hello to all,

I am interested in hearing how people are measuring the groove diameter of a slug pushed through a 5 groove barrel, such as my 686.

Any ideas of tips welcome.

Mike

[chris in va]

Here's how my brain works...

I'm sure there's a much better way of doing it, and the others will tell you. But I'd put the slug on a drill and spin it. Carefully place the calipers on the slug as it's rotating.

It's late, I'm tired...but just a thought.

[Trifocals]

Normally this is accomplished using a "V" micrometer. This type micrometer is most often used to measure the diameter of five flute reamers. There is another method involving the use of a "V" block, but I am not familiar with the procedure. LOL

[legi0n]

I've seen somewhere a hole gauge for sale. It had quite a few holes based on a given diameter. Like .357-001", .357-002", .357", .357+001" .357+002"... Quite expensive though.

[oneokie]

Hello to all,

I am interested in hearing how people are measuring the groove diameter of a slug pushed through a 5 groove barrel, such as my 686.

Any ideas of tips welcome.

Mike

To measure without specialized equipment:

# 1 Use a piece of flexible, but fairly stiff shim material (a strip of soda or beer can works well). Measure the thickness of the shim material and double this number.

#2 Wrap this piece of material around the slug and measure the diameter of the wrapped slug. Use a light touch with the measuring instrument, so as to not obtain a false reading.

#3 Subtract the measurement obtained in step #1 from the measurement obtained in step #3.

This gives you the groove diameter of the odd number rifled barrel.

[DWM]

Hi , if someone post how to use the V blok I'll appreciated , I read about this metod but never how to use the block..

Thank you

DWM

[Nobade]

I bought a V anvil mic on Ebay for cheap. I use it for bore slugs as well as measuring throat reamers and other 5 flute cutting tools. Seems there is less demand for mics like this than normal ones, so it didn't bring much money. New ones are really pricy.

[Rocky Raab]

I've used the "turn it by hand and adjust the mic until you can no longer can" method. Do it a few times on different places of the soft slug to avoid smearing and average the results. While not absolutely accurate, it is certainly accurate enough for our needs.

[runfiverun]

i'd just get close on the bore, and worry about the cylinder throats that's what's gonna make or break you anyways.
if your getting say 358ish with rocky's or nolan's method.
but 356 or357 on the cylinder throats you got issues to deal with.

[mdi]

I've used the "turn it by hand and adjust the mic until you can no longer can" method. Do it a few times on different places of the soft slug to avoid smearing and average the results. While not absolutely accurate, it is certainly accurate enough for our needs.

I've used this method as a machinist to measure parts that were slightly out of round or had chatter. Works surprisingly well...

[Pepe Ray]

Measureing a spinning object is a great way to ruin your calipers or injure your self -OR - both,

Watch for P.M. Shiloh.
Pepe Ray

[Rocky Raab]

Did you perhaps miss my "turn by hand" qualification?

[geargnasher]

Rocky, I think that was directed at Chris in Va, not you.

+1 on gently rotate the slug through the anvils of a micrometer, using a feather touch. The "lands" of the slug itself are usually wide enough to almost overlap a cross-sectionional measurement and can be felt accurately enough. Too much pressure on the thimble and they get rounded-off easily, though. Calipers aren't good enough in my book for meausuring slugs, for a tolerance of +/- .001" at best can give you a measurement far enough off to cause trouble. Even using calipers as a comparator doesn't come close enough in my book since .0005" over- or undersized can make a difference in accuracy, safety, and function.

As has been mentioned, I wouldn't sweat the groove dimension much, the cylinder throats are far more important for boolit size in revolvers. I only use the barrel slug as a point of reference for determining if the cylinder throats need to be reamed and, more importantly, if there is a restriction at the forcing cone from the barrel thread crush. Forcing cone restriction can be determined by driving one slug all the way through from the muzzle, and another one to within 1" of the forcing cone and back out the muzzle again and measuring the difference.

Gear

[Char-Gar]

I have been measuring slugs pushed through 5 groove smith and wesson pistol for many years with an ordinary 1 inch Starrett micrometer. I have read time and time again where, it can't be done but it can.

There is one very small spot of the trailing edges of the slug where there is full groove diameter. I open the jaws of the mike until it is a a couple of thousands smaller than grove and slowly rotate the slug with one hand and open the mic jaws with the other until there is just a kiss of a feel as the slug fully rotates past that sweet spot. It takes a little practice to get the feel.

Don't horse the slug through the jaws as you can mash the slug just enough to get a false reading.

I have done it scores of time and it works. To check, I have had folks check my measurements with their supper duper specialized tools and it is always the same as my method.

It continues to amaze me how many folks just take other folks word that this or that can't be done, when most of the time the folks that told them that are just repeating what they read or heard from somebody else. If everybody took no for an answer before they tried it for themselves, we would still be living in caves.

P.S..... I can save you all that measuring stuff. Just size you bullet as per below, drop the loaded round in your cylinder and it the plop right in go shooting and never look back.

38/357 MAG ... .358 or .359 is your mold is large enough to allow it.
44/44 Mag.... .431 or .432 if you mold is large enough to allow it.

[geargnasher]

Uh, Chargar, nobody was disputing that here, in fact you back up my post quite nicely. The only time I could see it not working is if the barrel had abnormally narrow grooves, which Smith's don't.

Gear

[Rocky Raab]

Reading back, I see that post that Pepe was probably referencing. Thanks, geargnasher.

I do think that a caliper that reads to .001" is plenty good enough, however. How often have we heard "When in doubt, size it a thousandth or two larger" when discussing the right size for cast bullets? If that's reasonable advice (and I think it is) then a caliper that reads to .001" ought to give us all the accuracy we need. We aren't fitting precision parts here. Lead is soft, deforms easily - in both directions - and we probably change its diameter when we cram it into the case, anyway.

[chris in va]

I'm not saying spin the sucker up to 1000rpm, just enough to keep the caliper from settling in a groove.

[BCB]

If you are a member of Cast Bullets Association and receive “The Fouling Shot” magazine, there is a gentleman in there who will measure the diameter of odd number rifling boolits for free…

Years ago I sent him a couple of slugs that had been imprinted with the rifling of a barrel that had odd number of grooves and he did the measuring…

Good-luck…BCB

[mpmarty]

and we probably change its diameter when we cram it into the case, anyway.

According to quantum theory we change the diameter by measuring it.

[felix]

Yeah, and the barrel changes diameter every time we shoot a boolit through it. ... felix