I've slugged the bore

[dddddmorgan]

In the interest of being more accuracy minded I followed the examples set here and I slugged my first revolver this morning.

I picked up a beautiful older (maybe 80's) Ruger Blackhawk in 357 Magnum. With a nice short barrel this is intended to be a packing around gun for camping and fishing.

So I slugged a couple of the chambers and they measure .3595". Do I need to do all of them or can I just assume for the rest?

I slugged the barrel and I not sure how best to measure it. I have a nicely engraved round ball and a nice Starret veneer caliper as well as a nice Lyman Micrometer. What's the best way to measure the engraved slug?

[rintinglen]

Especially on the older guns from Ruger, you need to do them all. They used to bore 3 holes at a time, with three reamers and they were bad at keeping them the same. You might have one new reamer, one half way through its expected life and one 10 minutes from the scrap bin making for three different size throats.

For the barrel measurement, you need a "Vee" block and the knowledge to use it, along with an appropriate micrometer for real accuracy. However, you can get close enough for most purposes by carefully positioning the slug in the micrometer, making several measurements and taking the average.

[dddddmorgan]

My Lyman Micrometer won't (can't) measure the rifling since the slug is a reverse image but it can measure the grooves. Can you expand on the "Vee" block?

I do have an RCBS Ball Micrometer if that would work at all.

Also I'm wondering if I don't care about the lands measurement just the grooves?

[rintinglen]

A V-block for measuring Purposes is a precisely squared and machined block of steel with a "v" shaped cut on one or more sides.. They usually come with a table that allows you to place the round object in the "vee" and measure the combined height and then determine the true diameter of the object. Mayhap one of our machinists can give a better explanation. I don't have one and haven't used one in over 50 years.

However, what you want is the groove diameter, not the bore diameter, so the outside measurement is what you need, and that can be fairly accurately measured with your micrometer. You may be off a few 10,000ths, but you won't be far enough out to matter with a cast boolit. Take four measurements, rotating the slug, and then average the three largest, you'll be pretty darned close.

But before you get too caught up in all this, shoot the gun with your intended loads. If you get the accuracy you want, and don't have a barrel full of lead, you save yourself a bunch of bother. But Uniform chamber throats shoot better and lead less, all else being equal.

[Larry Gibson]

Take a strip of soda/beer can 1/2" x 3" and wrap around the slug. Measure the diameter and then subtract twice the thickness of the can strip. Certainly not accurate to .0005" but it is accurate enough for measuring groove dimeters.

[dddddmorgan]

As usual the advice here is top notch and practically useful.

1. I slugged all chambers and the average for all 6 is .3588

2. I found my micrometer stand and I'm confident in the quality and accuracy of my Lyman micrometer. I have a "1-2-3" block and it measures very accurately and I adjusted zero.

3. Measuring the bore slug it averages out to .3582 (5).

I've learned over the years that averaging measurements like this, with the tools I have and my skill level that averages are a more accurate conclusion. Measuring that slug on six rotations I'm bound to catch all the grooves that make up the rifling and I reduce my error.

And FWIW the bore .3515 as best as my micrometer will measure.

Again, thanks for the help and on to the next revolver.

[murf205]

dddddmorgan, do yourself a favor and go to Amazon and buy one of the micrometer stands. I bought the one that looks like Donald Ducks bill with the thumb screw to hold the body of the mic. Best $19 this old fumble fingered man made on a long time.

[Gtek]

I appear to have pretty good results with the soda can method. Making then long enough to pinch in fingers and then slide hemostats up and latch, and that little padded jaw vice from Harbor Freight works pretty good for holding mic's.

[dddddmorgan]

Well I've slugged the bores on the 45 Colt again and everything is .4515 or a smidge less.

Standard .452 boolits and the occasional jacketed projectile at .451 will be fine, right?

Yes, all chambers and barrel slug exactly the same. Perhaps I got the first gun done with a new reamer before it wore out

And I don't recall that I mentioned, this is a brand new Ruger RSR Distributor exclusive, the 5.5" bbl stainless Bisley grip with 45 acp cylinder, everything is large, cylinders measure the old style large, lots of steel.