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Old December 2, 2010, 10:09 PM   #1
frumious
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Slugging the bore

I often see posts indicating the value of slugging the bore in order to find the optimal bullet diameter for a particular gun. I think I am ready to do that on my guns. Where might I find lead slugs (balls?) suitable for this? I reload but do not cast my own bullets, so I am unable to make slugging slugs myself.

-cls
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Old December 2, 2010, 10:14 PM   #2
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Lead fishing sinkers work well for slugging bores. Make sure you use a good amout of oil in the bore before slugging, and use a wooden dowel to push it through with.
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Old December 2, 2010, 10:25 PM   #3
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Sounds good. I'm not a fisherman. Are all LEAD fishing sinkers PURE LEAD? I'll probably just head on down to Academy (I am in TX) and look at their selection, anything to watch out for?

I will be slugging bores on the following calibers:

9mm
.45ACP
44mag
357mag

One more thing...do most guns have an even number of grooves? If not, how do you measure groove diameter on the slug? On barrels with an odd number of grooves the slug won't have two grooves directly across from one another.

-cls
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Old December 2, 2010, 10:30 PM   #4
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pretty much most lead sinkers are pure lead, or very close to it. If it seems to bit a bit small for the bore just set it down on a hard surface and give it a couple of taps with a hammer to flatten it a bit, this will also increase the diameter of it a bit. The egg sinkers tend to work well, as do the bullet type sinkers.
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Old December 2, 2010, 10:41 PM   #5
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Awesome, thanks!!
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Old December 3, 2010, 01:32 AM   #6
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For slugging bores, I use round balls. You can buy them at stores that sell muzzleloader suppliers. Use a brass rod on both ends of it to flatten the ball and fill ("slug out") the grooves.

Most firearms have even numbers of grooves. When you slug the bore, the grooves fill out and are the high spots, so miking the slug is easy.
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Old December 3, 2010, 07:17 AM   #7
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What he said.

Don't forget to oil that bore BEFORE sending a ball through.....

Use a quality ten-thou mike; measure repeatedly.

I use Hornady balls.
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Old December 3, 2010, 08:19 AM   #8
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"..sinkers are pure lead, or very close to it. If it seems to bit a bit small for the bore just set it down on a hard surface and give it a couple of taps with a hammer to flatten it a bit, this will also increase the diameter of it a bit."

Use one of the bullets you have and do the same thing without fooling with sinkers. Use your mike or caliper and only expand the bullet 3-4 thou, max, and driving it through a lube bore won't be difficult.
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Old December 3, 2010, 10:20 AM   #9
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In the past I've slugged bores on my revolvers by using a lead round ball (buckshot) harvested from a shotshell I've cut open. Obviously that's not going to work with all rounds, but it has worked with .32 and .38 Specials.

I've also pushed them through the bore by firing them into a bucket of water or other catch material, but propelled from a cartridge with about half a grain of fast powder, like Red Dot.

Obviously you need to be VERY careful about this, as even with that little powder you can still generate a fair amount of velocity.
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Old December 3, 2010, 11:34 AM   #10
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Several caveats and some emphasis to what's been said:

First, fishing sinker composition may depend on where you live. I've looked at them in Walmart and Gander Mountain and other stores here in the middle of Ohio and didn't find any in pure lead in the stores at all. They were all something harder. Beartooth Bullets sells pure lead egg-shaped sinkers for the purpose and slugging kits. NECO sells pure lead cast bullets for slugging in different calibers (last item on this page). Meister Bullets sells slugging kits.

Hornady swaged lead balls are pure lead. Get a ball that is oversize and roll it between flats until it is two or three thousandths over your expected groove diameter.

Whatever slug you choose, run an oily patch through the bore and oil the slug and use a short length of dowel rod (wood or brass) and a hammer to tap it in. Once the whole slug is in the bore, you can push it through with a cleaning rod or a longer dowel. I use brass rods from Lowe's usually.

Standard cast bullet alloys don't work well. They are too hard and elastic. They spring out against the bore and this prevents you from feeling constrictions and irregularities in the bore, which is half the purpose of slugging, especially in revolvers. I once tried using one and found it not only harder to push though than pure lead, but the pushing force stayed constant even if I put the bullet in for a second pass, where a lead slug revealed both tight and loose places in this bore. The micrometer reading was about three ten thousandths bigger for the cast bullet than for the pure lead slug in the same bore. That level of error will vary with the alloy, where pure lead produces a very accurate result. Some swaged lead bullets are still soft enough to do a fair job, but their composition is variable, so I don't want to suggest they all will. Lead (no plating) .22 rim fire bullets usually are soft enough to work for slugging .22 bores. You can bump their diameter up for a .224".

Let me emphasize the need for an OD thimble micrometer with a Vernier scale that resolves ten thousandths. And even with these, you need to wipe the anvils with a soft cloth and check where they zero to add or subtract that amount from the final reading. Calipers are not adequate. They are often off by a thousandth or so and the jaws and beam can deflect if your touch with them isn't delicate. We had one thread not long ago where the poor fellow was seeing readings that were off a couple of thousandths due to caliper limitations. You can use them to tell how one bullet compares to another, but the micrometer is much more reliable for absolute measurements. You do need to know how to read the Vernier scale. You can look that up online.

Smith & Wesson uses 5 groove rifling and the increasingly popular Obermeyer 5R rifling does, too. The theory is that two opposing lands squeeze and distort the bullet more than a single land opposite a groove will. The odd groove count thus allows the rifling to be deeper, according to Obermeyer. Enough accurate barrels have been made both ways that it is hard to believe it is a critical difference.

Measuring the slugs from odd-groove rifling can be a challenge. I measure each opposing land and groove diameter, then chuck the end of the slug in my lathe with the chuck gears disengaged and drag a dial indicator over the surface while I turn the chuck by hand. It tells me how tall the groove impressions are off the land (bore) impressions. I use the average value and add it to the other readings. You could do the same thing in a Sinclair type runout gauge by using a slugging bullet like the NECO's with a long enough impression area that you can stick it part way into a case for turning. There is also a more complicated method that involves using a v-groove and a depth mic calibrated with a pair of ground dowels of known different diameters, but depth mics don't normally resolve ten thousandths, so I don't like this much.
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Old December 3, 2010, 05:35 PM   #11
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Read here

Hope this helps.

http://www.surplusrifle.com/reloading/slug/index.asp
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Old December 3, 2010, 07:22 PM   #12
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Taking a semi-auto handgun for an example, does it really matter which way you slug the barrel?
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Old December 3, 2010, 10:21 PM   #13
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I find slugs can feel quite different depending on which way you start them in. If either end has a constriction, you won't feel much difference pushing from that end, but if you start at the wide end, the constriction is very apparent when you encounter it.
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Old December 3, 2010, 10:48 PM   #14
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Wow thanks guys! Esp. Unclenick...lots of good info as always. I will probably look around to see if I can find pure lead sinkers, then get some #8/9/10 if I do.

Main reason I started this thread is I have a .45ACP load that shoots like a laser out of my 1911, but spreads out quite a bit when shot from my PX4. I read a post last night about Penn Bullets and after reading on his site was encouraged by the fact that he sells any given bullet in so many different diameters. So maybe I'll end up building rounds specifically for each of these two pistols. And that starts with knowing the groove diameters of each barrel.

Again, thanks for the info!

-cls
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Old December 3, 2010, 11:48 PM   #15
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I just slugged the barrel on my XD 45 and I did what a guy on You tube did


I melted pure lead in a empty 45 auto case then used a kinetic puller and pulled the slug. While I was waiting for one to cool I made a second one. I drove one in from the muzzle just past flush then drove it back out, then I did it with my second one from the chamber end. One end was .450 and the muzzle end was .451. Hope that helps. Oh I used some Stick on wheel weights and some anchors for duck decoys.
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Old December 4, 2010, 09:48 AM   #16
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Frumerious,

Check this illustration. If you can seat your lead bullets out far enough so the round headspaces on the bullet instead of the case mouth, that usually maximizes accuracy and minimizes leading. Beyond that, you start to look at getting the gun accurized to whatever degree the design allows.

The other factor is the one Grubbylabs describes. If your barrel is narrower at the breech end than at the muzzle, it will tend to lead badly and shoot lead bullets badly. Jacketed bullets don't care so much. Firelapping or hand lapping will cure such a taper.
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Old December 4, 2010, 10:02 AM   #17
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Its funny you should say that since the only bullets mine shoots to point of aim are cast LRN's. Every thing else is low and left.

Not sure but their may be a loose nut on the trigger.
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Old December 4, 2010, 10:54 AM   #18
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Well, you've got me because you are using the term accuracy correctly where I did not. The correct technical term for how small groups are is precision, not accuracy, and it was group size and not its location that I was referring to.

In handguns, bullet weight has the most say over the vertical position of the group. Lighter bullets group lower, and your sights need to be adjusted for different bullet weights.

If the bullet weight is the same, low and left point of impact, for a right-handed shooter, usually means you are yanking on the trigger. You can test for this by having a friend load your magazine and slip a dummy round in somewhere that you don't know the location of. When the hammer falls on the dummy, you will see the front sight dive low and left if you are having this common problem. When a live round goes off, you can't see it because of the recoil. The movement always starts before the firing pin hits the primer, but it's all too quick for the eye to see without the dummy round. Ideally, you don't want to see the sight picture shift, jiggle, vibrate, or do anything when the hammer falls on the dummy.
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Old December 4, 2010, 11:39 AM   #19
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Unclenick, thanks, I have seen that illustration before. Problem is, I don't know that I have that much control over COAL. I have an RCBS Pro2000 press and I always have a little bit of variation in COAL. I get variation throughout the load process (1-2 thousandths, IIRC) and in the first couple and last couple through the press (4-5 thousandths, IIRC).

I read a thing where it indicated that since the shell plate on a progressive "floats", you need to try to make the resizer/decapper die and the seater die touch the shell plate when the ram is all the way up. That way since they are more-or-less right across from one another they will hold the shell plate down, and the COAL will only vary due to press flex, which should be a lot less.

Thing is, I have Lee dies, and the only two I can make do this are the resizer/decapper and the factory crimp die. The flaring die and the bullet seat/crimp die (which I am not using for crimping) are adjusted by how close to the shell plate they are when the ram is up. I can't adjust either of them down any further. If I adjust the flaring die down further, then it will flare way too much. If I adjust the seat/crimp die down further, it will start to apply crimp, which I do not want. I want to crimp separately to avoid shaving lead.

So I am not sure what to do to gain more precise control over my COAL. I do know that I am going to get rid of my factory crimp dies and switch to maybe Redding crimp dies - I read that the FCD swages the bullet and can ruin any accuracy you get out of matching bullet size to bore size. So I thought I'd try out a different crimper, like Redding's (but not the competition one - too expensive. Just the regular taper crimper.). But that doesn't help with the fact that I can't turn the seating die in any more. I wonder if I can take the crimping guts out of it? Or maybe I should buy a replacement seater die too. *sigh*

-cls

Last edited by frumious; December 4, 2010 at 01:12 PM.
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