Measuring slug from 5 groove barrel?

[fatelk]

Maybe I'm showing my ignorance, but is there a good way to slug and measure a 5-groove barrel? I don't see a good way to get a real accurate reading across the slug with my micrometer.

As best as I can tell, it looks like about .4305" if I try to line up the edge on one groove with the edge of the almost-opposite one. I'm surprised at that because I've always shot unsized Lee boolits through it (WW alloy, about .430 or slightly under) at magnum velocities, with no leading and good accuracy.

I like this old S&W 629. With the 8 3/8" barrel, I can usually impress people when I hit a 75yd milk jug pretty regular. This whole leading thing sure seems pretty complex. I get leading in my 700fps .45 loads with a boolit slightly over bore diameter, and no leading in 1500fps .44 mags with a boolit that looks to be slightly under?

[qajaq59]

You could try this method.
"Wrap the slug with thin shim stock; mike the shim stock first, it may not be "as advertised". Wrap the slug tightly,
and mike the resulting wrapped slug very gently, so you don't compress the shim stock into a groove in the slug
(which is an imprint of a land in the bore). Subtract twice the thickness of the shim stock, and that is the groove diameter."

BTW, I found that a long time ago and stuck it in a file, so it isn't something I dreamed up. However I don't remember who did.

[462]

The shim stock method is probably more precise, but didn't learn about it until after I measured my slugs by slowly rolling them in a micrometer while closing it, feeling for the least bit of resistance.

[Le Loup Solitaire]

Its in Phil Sharpe's book, "The principles and Practices of....." in the section of the measurement of 1917 barrels. LLS

[machinisttx]

I was trying to get a run of special V blocks made to make it easy to do this, but stuff came up and I haven't been in touch with them lately. Hopefully I'll remember to give them a call this week while I'm off.

[243winxb]

Line up the edge on one groove with the edge of the almost-opposite one works for me. Your close enough to the standard 44 mag. dia. of .430"

[fatelk]

Measuring as careful as I can (I worked as a machinist for a couple years), it sure looks like at least .4305". I guess it really doesn't matter because it shoots better than I can and leading is minimal. I did get some real light leading today after 30 rounds or so, but it brushed out pretty easy. I guess maybe I should cast them harder and size them to .431.

Half a box is really about all I can take with that thing any more. It just plain hurts my hand with heavy magnum loads, guess I'm getting wimpy in my old age.:)

I had a big chunk of lead I got recently, couple inches thick and the size of a frying pan, maybe 35 pounds. I wanted to try to bust it up some so I could melt it down. We took it out and shot it a few times. It didn't do much to bust it up, but I got some cool expansion out of my 250gr .44 boolits. I was surprised that they were soft enough to mushroom like this.

[462]

Fatelk,

Try a bigger boolit before you change alloy.

If your .45 is a revolver -- especially a Ruger -- slug the cylinder throats. Though the boolits are over bore diameter, they may be smaller than throat diameter.

While you're at it, slug the 629's throats, also.

[Edubya]

Fat elk, what lube are you using?
Where in the barrel are you getting the leading?
BTW, if I need any more than 1,300 fps, I'll use a long gun. Maybe I'm a wimp too.
EW

[fatelk]

The only lube I have for my ancient Lyman 45 is the equally old Lyman black lube that came with it. I know there is better lube out there; I just haven't bought any yet.

After 30 rounds or so, the leading is just a slight smear in the second half of the 8 3/8" barrel, and cleans out easy. I don't know what a couple hundred rounds would do without cleaning, other than break my wrist. I normally don't load them up to the max like this, just thought I'd see how fast they could go without leading.

I did slug one of the cylinder throats on the 629, and it measured over .435". Is this fairly normal, .435" throats and .431" bore on a .44 magnum?

The .45 I referred to is actually a Ballester Molina .45 acp with a Colt series 70 barrel. I smeared some black Lyman lube on a bunch of my tumble lubed boolits and shot a box yesterday. No leading at all now. Before giving up completely on the alox/jpw lube, I'll try a third coat on them and see if that works.