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View Full Version : Measuring 5 groove Bbls.



Pepe Ray
11-14-2006, 02:08 PM
FYI,
This is NOT my idea. I got it from a American Rifleman art'l. via the cast bullet hand book. The question has cropped up here frequently, but has never, AFAIK, been answered completly. Here goes.
Needed tools;
#1, accurate michrometers or calipers. Not specialized.
#2, a V block
#3, the equasion
#4, stuff to calculate with, ie, paper & pen, calculator or PC software?
The V Block is the tuff part for those of us w/o machining resources. If youve got a buddy w/a shaper or milling machine and knows how to use it, your IN.
Others will need to hire it done.
The block is made from any kind of stable material. Preferred steel or brass. It must be of a size to allow the spanning of your michs or calips. Mine is from 1/2 in. square bar stock. (I think cold rolled.) The V groove must be 108 degrees for 5 groove bbls.
The formular gives a dimension (B) which is then multiplied by a constant to give the desired diameter.
A-C=B Where A=The initial mesmnt. of slug from bbl as it lies in V block, evenly of course. Subtracting C (a constant =.3332 ), gives us B which is then multiplied by a constant .8944. This will give you the answer.
Being somewhat anal, I usually roll the bullet in the block 5 times to get 5 msmnts for an average, Then use the average for my A.
If the bulet is long enough, you can use a small rubber band to hold it in the blocks while you rotate and measure.

For other odd numbered groove bbls. the V groove size must be recalculated.
Pepe Ray

Ricochet
11-14-2006, 08:34 PM
I think that V-block method is in the old Lyman manuals, too.

mag_01
11-15-2006, 09:09 AM
I think knowing your bore diameter is probably a good place to start----But putting the largest diameter boolit down the throat of that rifle is where you want to be for best performance----measuring the inside diameter of a fired case is a good place to start-----a boolit .001 or.002 over that is probably the best condition----increase diameter until it dose not fit or chambers with difficulty then back off a little---hope this helps---good luck----------Mag

Larry Gibson
11-15-2006, 10:59 AM
To measure slugs from 3 or 5 groove barrels an easier method is to take a strip of.002 or.003" shim stock 1/2" x 3" and simply wrap it tight around the slug from the bore holding the two ends together. Mic the outside diameter and subtract twice the thickness of the shim used. Pretty simple, pretty effective and quite accurate.

Larry Gibson