Why does a minie ball tumble?

[Mike Hale]

I posted this in the wrong thread a few minutes ago and I think it should go here......

573 Why?
....Rapine .575, sized and soft lead; using 48 grains of 3F Goex at 50 yards on a clear and calm day.....app 2 like this out of app 40 rounds fired?

Why, oh why?

[Edwin Flint]

Most likely, the lead is not pure lead. While lead often appears soft, it is not actually pure lead. The bullet also may be too small for the bore. The minie should be no more than .002 under bore size.

If one or both, you can get the key hole shown on the target.

[Bruce Cobb 1723V]

2 other possibilities ...... your skirt is coming apart at the muzzle, a flaw in your bullet casting or your crown needs to be redone.

[Gary Van Kauwenbergh, 101]

The most probable cause of tumbling is lead that's too hard. Undersized bullets, split skirts and bad crowns are possible, but by far the most likely cause is the lead.

Back in the days before I owned a lead hardness tester, I cast 1,300 perfect bullets from my Parker-Hale bullet mold (the type you had to remove the base plug manually) using lead that I thought passed the 'thumbnail' test. It turned out the lead was just a little too hard, and I was getting the same results as you are now. I had to melt everything down and use the lead for carbine bullets. I decided if I was going to use lead from anywhere other than a certified source, I ought to own a lead hardness tester.

I've found that lead sources that used to be absolutely trustworthy, like telephone company cable sheathing and x-ray room plating, are no longer totally soft. I always suspect lead pipe, and anything from a scrap dealer. I can get all the free lead I want from a couple stained glass places in town. If you catch them re-doing an old church window, it's great, but if you're getting the scrap caming left over from their classes, you have to watch out for alloyed metals.

Regardless of where it comes from, it doesn't go in my pot until it's gone through my hardness tester. I've tried Lee, Sako, and a Real Tree testers, but like the LBT ones best: http://lbtmoulds.com/hardtester.shtml

[gmkmd]

Definitely agree with above. But, having your bullets too undersized can do it, too. When I shoot my Plymouth, with a bore diameter of 0.685, I size my bullets 0.683. I usually have no problems, but once in a while the first shot from a clean, cold barrel will keyhole. So I during individuals I'll usually fire a fouling shot or two into the berm first. Alternatively, I could try using an 0.684 sizing die, but havn't tried yet.

The best way to tell if you are shooting the right sized bullets is to get an accurate measurement of your bore diameter. I think the only way to do that is to use a set of machinist's plug gauges. This is a set of steel plugs in incremental sizes by the thousandth. You simply see which size fits in your bore, and you've got your bore diameter to within half a thousandth. Much more accurate than trying to use a vernier.

[Todd Harrington, 3637V]

Or a v-groove micrometer

[ms3635v]

Hey Frank (Mike). I've been looking at the photo you attached for the last two days and I wanted to know if that is a Rapine or Hodgdon minie. I have used both minies over the years and the one in your picture sure has the profile of a Hodgdon bullet and does not appear to have the profile of a Rapine minie. In some cases, the Hodgdon bullet will tumble or keyhole if the powder charge is too light or the lead is too hard. The Hodgdon bullet has a thicker skirt than other style minies but are still good performers providing you use good, soft, lead and the right powder charge. I have recovered Hodgdon minies fromm the backstop at my range and in some instances, upon examination, the minie has little or no rifling engraved in them from firing. My son-in-law was shooting a Hodgdon bullet in his Whiteacre barreled LG&Y, but we changed to a Rapine 580460 Old Style minie and got much better results. The Rapine minie has a thinner skirt and expands very well producing excellent groups and consistent performance.

[Pat in Virginia]

An alternative approach to buying and using plug gages is to use your sizing dies assuming they size reasonably accurately. You will need them in increments of.001. Size a number of bullets varying in steps of .001 and see which ones are the go and the nogo at the muzzle.

Now you may think that you can't trust the sizing dies to be absolutely true to size. That is true, but they are the ones I use to size my bullets so I may not know the exact diameter of the die but I do know what the size is of the bullet they produce, and therefore which of my sizing dies I should use and that is what counts. Also, I do check the results of my sizing dies with good calipers and a micrometer so I have a pretty good notion of how true they are.

I keep a number of sized bullets on hand with their diameter writen on their base with a CD/DVD Marker Sharpie. It works on lead too. I recently used this approach to determine what the apparent bore (land to land) diameter was for an original LACo rifle: .580 for about .25 inch and then .579 according to the sizing dies I will be using to size the bullets for it. So I'll start by using my .579 sizing die and then go to .578, etc. to see what happens.

I found the .580 reading interesting as it will help to start a .579 bullet. Accuracy remains to be determined, but I will be using a rather thick wad column (greater than .25 behind the Gardner bullet I will test with first. Point being, I think the wad column will help to keep the bullet true to the bore as it leaves the barrel. Testing will tell the tale.


Pat in Virginia