How to measure a bore slug?

[Mike W1]

Searches are doing me any good so I'll ask here. Slugged the bore and want to "mic" it for the groove diameter but I really can't tell if I'm getting a groove on both sides of the slug or a land and a groove. Seemed like I read somewhere long ago there's a gizmo to lay the slug in and you measure that and subtract the fixed value and bingo you've got your groove measurement.

If there is such a thing what's it called and where do you get one?

[dondiego]

Try a thin wrap of aluminum like a soda can. Measure the thickness, wrap around boolit and measure, subtract 2X the thickness.

[JSnover]

Like dondiego said, just wrap it. The proper tool (as far as I know) is a v-block. It has to be the correct size for your caliber, or you have to plug in the sizes for the formula, something like that.
A ring gage would probably work if you knew someone with a set.

[Digital Dan]

Wrapping as posted above will provide groove diameter, but not the bore. With minor diligence one can fathom bore and groove from a slug using a micrometer if it has an even number of grooves. Bore can also be found with a pin gauge though I'd guess a full set of those suitable for .17 to .50 caliber would be somewhat expensive. A vee block and a bit of trig can work out the groove diameter for barrels with an odd number of grooves.

[dondiego]

I used to use a set of pi tapes at work. You wrapped the pi tape around the round item to be measured and read the diameter from the tape and it was accurate to 0.001 inches.

[mdi]

If you have much experience with a micrometer, you can turn the slug while lightly closing the mics. I have done a couple 5 groove barrels and can usually get within .001"...

[Pepe Ray]

Mike W1;
Hi, I'm going to try to post an image for you to see a "5 L&G V-blok".

114430
O.K., that's a start. I'll dig up the original reference if you need it.

Got one more to try. Stand by!! Well it's not going to post.
You can get a detailed report by finding the Handgunner Magazine website and looking up Mike Venturino's recent articles.
Ken (45Nut) used to have a stock of the V-bloks. He sent one to Mike who wrote a piece about using it, with pictures.

If you need more info, P.M. me but don't expect a quick return as I'm going on vacation tommorrow. BBI a week.

Yeah, you can wrap a slug, if you've got enough fingers and patience.
Good luck,
Pepe Ray