When slugging a barrel...

[Stick_man]

how much over nominal bore size do you make your slug? I was wondering if .01 is too much for a smaller caliber barrel (.224 or .243). Any thoughts?

[Iron Mike Golf]

You said "bore diameter". That means (to me and many others) diameter mesured at the top of the lands. If that is your reference point, then the answer to your question depends on the depth of the rifling.

[Stick_man]

Yes, I meant the bore, not the groove. My basis is that you have the nominal bore size and are trying to find out what the "groove" diameter is by slugging it. I realize that different rifling cuts produce different depths of rifling, so I was wondering how much bigger to make the slug.

The other reason behind my question is I was thinking of making a "slugging mould" by drilling some holes into a piece of 2x4 or 2x6. I want to start casting for my 6mm Rem and was thinking of using a 1/4" drill bit. Was wondering if .250 would be too much to be able to use for slugging a barrel with a nominal bore of .244 or if a slug measuring .3625 (5/8") would be too much for a .38 Special.

[MikeS]

If using pure soft lead I don't think you have to worry too much about the slug being too big. When you pound it into the barrel it will deform to fit the barrel, with excess shaving off. I slugged the barrel on a 30 cal rifle using a slug cast in a 38 cal mould. You can also just cast a slug of pure using any of the moulds you have for that gun, and before putting it in the barrel just tap it with a hammer to 'bump up' the size a bit so you're sure it's big enough. You wouldn't want to slug a barrel with something too small, but too big shouldn't be a problem.

[williamwaco]

If using pure soft lead I don't think you have to worry too much about the slug being too big. When you pound it into the barrel it will deform to fit the barrel, with excess shaving off. I slugged the barrel on a 30 cal rifle using a slug cast in a 38 cal mould. You can also just cast a slug of pure using any of the moulds you have for that gun, and before putting it in the barrel just tap it with a hammer to 'bump up' the size a bit so you're sure it's big enough. You wouldn't want to slug a barrel with something too small, but too big shouldn't be a problem.



That's what I do.

[Bret4207]

If you want an accurate reading you need to upset the slug into the grooves once you get it in the barrel. Just pounding it through may or may not get you to the bottom of the grooves.

[captaint]

I like to use the softest lead I can find. If too small, just beat it with a hammer until it gets large enough (like at least .005 larger than suspected groove dia.) If it's too big, roll it between hard surfaces to make it smaller. I don't like to leave them really large. Makes it harder to get it going.... JMO. Mike

[ElDorado]

If you want an accurate reading you need to upset the slug into the grooves once you get it in the barrel. Just pounding it through may or may not get you to the bottom of the grooves.

What are you saying, Bret? Should I pound the slug into the bore, and then hold it in place with one rod and pound it some more with another rod from the other end of the barrel? Or something like that?

[caseyboy]

Pull the lead bullet from a 22lr round. Perfect for the 22 cal rifles. I used one to slug my 7mm. I set the bullet on it base, and tapped the nose until it "blossomed out" to .290". Instant 7mm slug!

[Bret4207]

What are you saying, Bret? Should I pound the slug into the bore, and then hold it in place with one rod and pound it some more with another rod from the other end of the barrel? Or something like that?

Pretty much, yes. Put a light film of lube in the barrel, establish the area you want to measure, put a rod in to use as an anvil and upset it into the grooves, then knock it out. It's obviously harder to do this with revolvers, lever, pump and auto rifles, but it's certainly more accurate. It's also part of the reason I don't slug until I see a need to do so. I've found in most cases measuring the case mouth of a cartridge fired with a full power load will give me the max. diameter I can easily use. I start about there and can work down if needed.

[ElDorado]

Pretty much, yes. Put a light film of lube in the barrel, establish the area you want to measure, put a rod in to use as an anvil and upset it into the grooves, then knock it out. It's obviously harder to do this with revolvers, lever, pump and auto rifles, but it's certainly more accurate. It's also part of the reason I don't slug until I see a need to do so. I've found in most cases measuring the case mouth of a cartridge fired with a full power load will give me the max. diameter I can easily use. I start about there and can work down if needed.

Thanks, Bret.

I had envisioned trying something like that when I tried slugging a barrel and the slug essentially fell through the bore once I got it started. I guess there was a tight spot where I started.

That’s also interesting info about the case mouth. I’ll be trying that out, too.

Thanks again,
Jeff

[williamwaco]

I've found in most cases measuring the case mouth of a cartridge fired with a full power load will give me the max. diameter I can easily use.



That is a great idea. BUT how do you do it?

I have found that it is not possible to measure the inside of a round object using dial calipers because the inside "feelers"
( I don't know what to call them) are square and touch only on their corners, resulting in a reading that is smaller than the actual diameter. Like this ([

I can't draw it, does this give a clear picture of what I mean?

[ElDorado]

I believe you are correct, although the error may be minimal. There are various types of hole and pin gauges that can be used in lieu of calipers. Since you’re obviously using calipers, why not try a little math?

My Machinery’s Handbook is at my work place, but I know there is a formula in it that will allow you to determine the height of a segment of a circle, which is that small space between the face of the caliper jaws and the inside of the case. A quick google found this calculator that can figure out that difference. It seems to be quite a bit easier than using the formula in Machinery’s Handbook.

http://www.1728.org/circsect.htm

http://i1202.photobucket.com/albums/bb364/ElDoradoJeff/ForumPics/circsect.gif

If you look at Circle Two on the calculator web page, you can see that the green area is the part missing in the inside diameter measurement with calipers. You need to find the distance defined by line ED.

The easiest way to do this with a caliper is to determine the chord length, or the line defined by AB, and the apothem, the line defined by OE.

The chord length is simply the width of the face of the jaws on your calipers. My calipers are about .025”. Let’s say you measure the inside of the neck of a 30 caliber case, and that measurement is .310”. Divide that number by 2 to find the apothem, which would be .155”.

In the circle calculator, select the dot next to “Chord & Apothem”. Then input your information and select “Calculate”. In this case, the segment height is calculated to be .0005”, and it also shows the radius to be .1555”. Multiply the radius by 2 to get the diameter, .311”.


Or, to make it easy, you could just add about .001” to make up for the slop in caliper measurements.

Jeff

[williamwaco]

I believe you are correct, although the error may be minimal. There are various types of hole and pin gauges that can be used in lieu of calipers. Since you’re obviously using calipers, why not try a little math?

My Machinery’s Handbook is at my work place, but I know there is a formula in it that will allow you to determine the height of a segment of a circle, which is that small space between the face of the caliper jaws and the inside of the case. A quick google found this calculator that can figure out that difference. It seems to be quite a bit easier than using the formula in Machinery’s Handbook.

http://www.1728.org/circsect.htm

http://i1202.photobucket.com/albums/bb364/ElDoradoJeff/ForumPics/circsect.gif

If you look at Circle Two on the calculator web page, you can see that the green area is the part missing in the inside diameter measurement with calipers. You need to find the distance defined by line ED.


The easiest way to do this with a caliper is to determine the chord length, or the line defined by AB, and the apothem, the line defined by OE.

The chord length is simply the width of the face of the jaws on your calipers. My calipers are about .025”. Let’s say you measure the inside of the neck of a 30 caliber case, and that measurement is .310”. Divide that number by 2 to find the apothem, which would be .155”.

In the circle calculator, select the dot next to “Chord & Apothem”. Then input your information and select “Calculate”. In this case, the segment height is calculated to be .0005”, and it also shows the radius to be .1555”. Multiply the radius by 2 to get the diameter, .311”.


Or, to make it easy, you could just add about .001” to make up for the slop in caliper measurements.

Jeff


Jeff,

Thanks for that. I am seriously embarrased. I have a BS in mathematics and an MS in computer science. Many times I have thought about doing the calculations but was just too lazy. It never occurred to me that I could have found that formula in one of my math handbooks - let alone GOOGLE it. I guess I owe you a steak dinner. Next time you are in the neighborhood stop by.

Just tried it on .357 magnuem case. The diameter of the bullet fired from it was about .3565. (.356 die) The calculator calculated bullet diameter should be .3572.
Incidentally, bullets sized .3574 ( .357 die ) produce best results in this S&W M-19.

[geargnasher]

I do what Bret does as far as checking the inside neck diameter of a fired case to determine the maximum safe diameter that the boolit can be. I also make impact slugs of the rifle chambers using annealed cases filled with WW metal to halfway up the neck, and soft lead slugs cast from heavy-for-caliber boolits seated in the necks. Between the slug neck measurements and the ID of twice- or thrice-fired factory brass I get a pretty good idea of what's going on in there. To measure the neck ID, first I remove the crimp by belling the mouth slightly with a Lee Universal "Expander" die, then test-fit sized boolits in there. If my largest boolit is still loose, I "bump" it a bit with a hammer/anvil and try again. Once I get a snug fit, I mic the boolit. Inside calipers are really only useful if double-checked with a good mic before taking the initial measurement, or taking the measurement and locking the calipers and measuring the anvil spacing with a mic.

Gear

[Bret4207]

Jeeze, I was using that as a ballpark figure of the max size a boolit could easily use without thininng case necks, etc. But FWIW the thinner the blades the less the issue mentioned.

[ElDorado]

Jeeze, I was using that as a ballpark figure of the max size a boolit could easily use without thininng case necks, etc. But FWIW the thinner the blades the less the issue mentioned.

And the same goes for a larger diameter.

I knew more than one person would be slapping his forehead over that convolution about the calipers. My answer to williamwaco’s question was more of an academic one than a practical one.

The last line of my reply, “just add about .001” to make up for the slop in caliper measurements”, is more in line with my approach to the question.

We all fuss over things to different degrees. Sometimes I’ll see someone doing something that I think is just sloppy, and the next minute he’s fretting over some trivial detail. It’s important to have confidence in your methods, just so you can have peace of mind, and peace of mind is an underrated thing.

Jeff

[geargnasher]

Some written descriptions sound a lot more complicated than they really are sometimes, too! Someone might say "Geez, you go through all of that?", when in effect it's only a few motions.

Gear

[Lead Freak]

I've never slugged a barrel. I have a general idea, but what type of rod do you use to protect the bore when you do it?

[44man]

I've never slugged a barrel. I have a general idea, but what type of rod do you use to protect the bore when you do it?
I use brass. I have used steel but I wrap it with electrical tape or a long piece of shrink tubing. You do not need much force to upset the slug.
File the ends of the rods to remove any edges. Brass can touch the bore but not the steel.
I use hard steel ram rods to clean but always with bore protectors.
Don't fool with wood or aluminum and never a cleaning rod.
You want a rod close to bore size.

[old turtle]

I am no expert on slugging a barrel but I have done it several times. Use and over sized chunk of SOFT lead as many others here have stated. With soft lead you can use a wooden dowel smaller than the bore size. Of course my advice is often questioned by my wife.