slugging with an odd number

[fiatmom]

What is the best way to slug a barrel with 5 lands and groves.
I can only seem to get one land and one grove?
I tried to catch the edge but that did not work.
The rifle I am trying to slug is a Spencer carbine.
Nick
PS
I slugged a 30 cla barrel and found it to be 308.5 to 309 (onr land was larger) would a 310 sizer be appropriate.

[The Double D]

All the engineers and machinist will give you some pretty fancy ways to do it. The way I do it was taught me by an old mill wright. He taught me to work to tolerance called MIF- make it fit.


Here how you do it. You need a dial caliper. Hold the slug in the loose jaws of a dial caliper and roll it around between the jaws of the caliper. keep light thumb pressure on the jaws and watch the dial jump up and down. Note the high reading that repeats. That is the major diameter of you odd sized slug.

[Bob S]

I wrap the slug with a piece of thin shim stock, .003 to .005. Mike it first because it's not always "as advertised". Wrap the slug tightly and carefully mike the resulting "assembly". Subtract twice the thickness of the shim stock; that's the groove diameter.

Resp'y,
Bob S.

[mdi]

All the engineers and machinist will give you some pretty fancy ways to do it. The way I do it was taught me by an old mill wright. He taught me to work to tolerance called MIF- make it fit.


Here how you do it. You need a dial caliper. Hold the slug in the loose jaws of a dial caliper and roll it around between the jaws of the caliper. keep light thumb pressure on the jaws and watch the dial jump up and down. Note the high reading that repeats. That is the major diameter of you odd sized slug.

This is the way I've always measured round or semi-round parts. Worked as machinist for about 12 years.

[462]

flatmom,

I'm not a machinist, but I do it the same as The Double D and mdi.

Just a guess, but if the slug is of soft lead, tightly wrapping it with metal may cause some distortion and result in a false reading. Perhaps something like tape might be better. Again, only a non-machinist's perspective.

[The Double D]

The problem with wrapping with shim stock around small objects is that if the shim stock is thin enough to wrap around it will also collapse over the land and give a small reading If it is rigid enough to resist collapse it won't closely lay on the slug and read large. Then there is all that math and fussing , when you could just direct read out from your dial.

Ther are other ways. To measure a five groove slug with a V-mike you need a 72 degree anvil. Ring guages will work if you have a set. Sine blocks can also be set and the slug measured.

[machinisttx]

The correct way is by using the appropriate V anvil micrometer. look here, you want one for a five flute and not three (http://www1.mscdirect.com/CGI/NNPDFF?PMPAGE=1294&PMITEM=06232953&PMCTLG=00)

Alternatively, right angle trigonometry would get you very, very close.

[StarMetal]

You make a small metal V out of a little strip of metal say 3/8 inch wide and inch or so long. You bend it to a 90 deg V. You want the metal thick enough because you have to file that outside pointy elbow of the V flat, concentric to the two legs. After you finish you take a 30 caliber bullet and mic it. Write that figure down. Then you take that V and put that 30 cal bullet inside it and you mic the two together. See where that flat is important? The flat is against one anvil of the mic and the other movable anvil is against the bullet. Write that figure down and subtract the two. Next mic the five groove bullet you want to know the groove diameter of. Then merely subtract that difference you got initially between the V and 30 cal bullet and just the 30 cal bullet. Example: Say your 30 cal bullet mics .308. Then in the V tool it mics .333. The difference is .025. Now you mic your five groove bullet in the V tool and you get say .339. Subtract that .025 difference and your five groove bullet diameter is .314. Lot more accurate then calipers and lot less expensive then a V mic.

Joe

[Morrison Machine Shop]

All the engineers and machinist will give you some pretty fancy ways to do it. The way I do it was taught me by an old mill wright. He taught me to work to tolerance called MIF- make it fit.


Here how you do it. You need a dial caliper. Hold the slug in the loose jaws of a dial caliper and roll it around between the jaws of the caliper. keep light thumb pressure on the jaws and watch the dial jump up and down. Note the high reading that repeats. That is the major diameter of you odd sized slug.

This would be the way I would do it, machinist for almost 23 years.

[Jbar4Ranch]

A V-anvil FIVE FLUTE MICROMETER (http://cgi.ebay.com/Mitutoyo-5-Flute-V-Anvil-Micrometer_W0QQitemZ250499288386QQcmdZViewItemQQpt ZLH_DefaultDomain_0?hash=item3a52ebcd42&_trksid=p3286.c0.m14) is soooo much easier.

[Rocky Raab]

An anvil and a special purpose micrometer? To measure ONE slug? You guys work for the government?

This isn't a life-dependent measurement, for Pete's sake. Close is more than good enough. And if it turns out not to be, the only expense is one more sizing die. Peanuts.

Yet another example of allowing our brains to get wrapped around an axle while losing sight of reality.

[largom]

An anvil and a special purpose micrometer? To measure ONE slug? You guys work for the government?

This isn't a life-dependent measurement, for Pete's sake. Close is more than good enough. And if it turns out not to be, the only expense is one more sizing die. Peanuts.

Yet another example of allowing our brains to get wrapped around an axle while losing sight of reality.


Called "Pole vaulting over a mouse turd"
Larry

[StarMetal]

My little V-tool is so much cheaper and accurate...it's free if you have the piece of metal to make it from. Here's a pic to give you an
idea of how it works.

Joe

http://i245.photobucket.com/albums/gg51/starmetal47/V-Tool-1.jpg

[Rocky Raab]

In calibers .30 and above, groove depth is usually .004" (.300" bore has a .308" groove diameter). So measure the slug from groove to the opposing flat, add four thousandths and call it good enough. Gnat's ass precise? Nope. Precise ENOUGH? Heck, yes.

[StarMetal]

In calibers .30 and above, groove depth is usually .004" (.300" bore has a .308" groove diameter). So measure the slug from groove to the opposing flat, add four thousandths and call it good enough. Gnat's ass precise? Nope. Precise ENOUGH? Heck, yes.

Probably why you don't shoot small groups....not precise enough.
:kidding::kidding:

Joe

[405]

Agree with shim stock method. Just wrap once and pinch lightly between fingers so as not to depress shim into "grooves" on slug. Measure, subtract 2X shim thickness=~ groove diamter. Do it a few times to get feel for it and insure accurate/precise measurment. For bore dia. just take plunge tip (depth gauge) on caliper and measure height of "land" on slug. That is groove depth. 2X that meaurement and subract from groove diameter already taken=~ rifle bore diameter. Also, spinning a slug between jaws of mic or caliper works. Requires more touch and feel. And do it a few times to insure precision. A mic or caliper with a floating dial indicator (with a light spring!) works best for this as it gives visual indicator of high measurement.

I don't think that .0001" or better precision is required for this stuff. Size bullet to about .001" over measured groove dia. and fire!

And I don't use a .0001" mic to measure the diameter of a cinder block but my good guns are pretty accurate anyway.:kidding:

[Larry Gibson]

I also use the shim method. A strip of beer can works fine, just mic it to get the actual thickness. I had access to a shop mcrometer once that was very accurate and made some comparisons to the shim method. I found I ws within +/- .0002-3. Most often I was on the + side which meant the bullet was actually .0002-3 smaller than my measurement.

Since the general concenses was to size .001 over groove diameter I thought I was good to go. I then found, through extensive testing, that .003 over groove diameter almost always gave the best accuracy. Then I found, like many others, that the groove diameter is nice to know but but the real diameter to fit the cast bullet to is the throat. Thus I generally no longer "slug bores" but instead slug the throat and fit the cast bullet to the throat.

Larry Gibson

[machinisttx]

An anvil and a special purpose micrometer? To measure ONE slug? You guys work for the government?

This isn't a life-dependent measurement, for Pete's sake. Close is more than good enough. And if it turns out not to be, the only expense is one more sizing die. Peanuts.

Yet another example of allowing our brains to get wrapped around an axle while losing sight of reality.

Actually, I do work for a DOD contractor. That said, I started out as a machinist in a toolroom making stuff for stamping dies and die cast molds...typical tolerances of +/- .0002" and occasionally going to +.0001 -0.00 or the reverse. The right tool for the job makes life so much easier.

Personally, I'd use my friend, Mr. Trigonometry, rather than spending $300 on a new mic that I would rarely use.