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American Handgunner May/June 2012 Digital Edition - Page 42
SHOOTINGIRON thumbbustin’musingsfromtheduke mike“duke”Venturino Photos: Yvonne Venturino n the last issue, I wrote a “How-To” about slugging handgun barrels. I finished it by next comes the measuring and the saying measuring a slug from a barrel with an odd number of grooves is more difficult math. If duke can do it, anyone can, because the grooves don’t oppose one another. Let me begin with a brief overas long as they have a V-block, can do view of slugging a barrel for those who might not have read the last issue. simple math and can run a caliper. A great many handguns have barrels with actual groove diameters varying from their nominal specs. This was common in bygone times, but still is with some foreign pistols and revolvers. Forget all about it if you’re going to only shoot factory-made jacketed bullets because you can’t vary from the sizes manufacturers offer anyway. The place slugging is beneficial is with lead alloy bullets, especially those made yourself. Commercially sold lead alloy .45-caliber bullets can be commonly had measuring .451", .452" or .454". If you’re casting them yourself you can also size them to .450", .453" or .455". Slugging a barrel is ultra simple. It consists of merely pounding a piece of lead down the handgun’s barrel and measuring it. There are a few caveats to consider. First, use only pure lead for your slug. Second, tap it into the barrel’s to begin slugging a barrel, you’ll need something muzzle with something non-metallic, such as a weighted rubber hammer or a non-metallic to hammer with, and a pure lead hardwood stick. Next, tap it on through with a piece of wooden dowel. Don’t slug significantly larger than the bore to be use a metal cleaning rod! And don’t let the slug bounce off the floor as it exits slugged. duke likes to use round lead balls. the barrel as being so soft it will be deformed. sLUGGInG IT OUT: PArT 2 I nd here’s my own personal tip. Pure lead round balls as sold for cap-and-ball pistols make perfect slugs, but use ones considerably larger than the barrel to be measured. This way the slug gets a good length of parallel sides to measure. For instance, to slug .44-caliber barrels I always start with a pure lead round ball measuring from .451" to .457". For a demonstration, I slugged the barrels of a S&W revolver because, to the best of my knowledge, all that company’s revolvers have 5-groove rifling. This sample was an N-frame .44 Special, 2nd Model Hand Ejector made in 1929. I had never slugged it previously, having been satisfied to accept S&W’s nominal spec as .429". A .457" pure lead round ball was tapped through the .44’s barrel. Now this is where the skill of a machinist and knowledge of mathematics comes into play. By the way, I don’t have either one. Once, after writing I was unable to measure a slug accurately because it came through a barrel with an odd number of grooves, I received an e-mail from a reader named Ken Caldwell. He has both machining skill and math knowledge and he offered to make me a V-block so I could measure barrels with an odd number of rifling grooves. What a V-block consists of is a small piece of steel with a V-shaped trough cut into it. The slug rests in that. Once nestled in the V-block, a formula is used to determine the slug’s diameter. “A” is the measurement from the bottom of the block to the top of the slug. “C” is the distance from the bottom of the V-shaped trough to the bottom of the block. “C” is subtracted from “A” to get the value of “B.” “B” is then multiplied by the constant .8944 to get the diameter of the slug. Ken also told me “C” is always unique to each V-block, but I don’t know how to determine it! 42 a Duke’s Secret A V-block like this one is needed to measure slugs from odd-numbered rifled barrels. or the .44, my “A” measurement was .826". My V-block’s “C” measurement is .34658". Subtracting “C” from “A” gave a figure of .47942”. That multiplied by my V-block’s constant of .8944 gave the measurement of the slug as .42879". Since my calipers are only hobby grade, which can safely be rounded off to the nearest thousandth — or .429"! And The Answer? F * WWW.AMERICANHANDGUNNER.COM • MAY/JUNE2012 If I’ve peaked your interest, V-blocks are available from online sources like www.brownells. com or www.midwayusa.com, and other sites offering machine tooling.