Measureing a five groove bore

[1951]

Good morning,
I'm having trouble measuring slugs tapped through a five groove barrel. I spun the barrel off my 1863 DOM 1858 Remington Army revolver to slug the barrel. The rifling is five right. I can measure straight across from a land to a groove with my calipers but having a hard time trying to get a measurement groove to groove. I tried going from the edge of one groove to the middle of another but don't know if I'm going straight across. Is there a special tool for doing this?

My land to groove measurement is .442, so I know the groove is deeper than that and the lands are less than that, but I'd sure like to know what the measurements are.

Any suggestions?
Thanks.

 

[butchlambert]

You can measure the bore with pin gauges.

 

[paperpuncher]

I think you need a 3 point micrometer

 

[paperpuncher]

If you have set set of pin gauges you could probably get by with a depth mic and a view block

 

[butchlambert]

An micrometer or depth mic will not fit in a barrel. A View (vee) block won't either. You can cast the bore and grooves and then measure it.

 

[paperpuncher]

I thought he slugged the bore and was having an issue measuring the odd # of grooves kind like a 3 flute endmill

 

[butchlambert]

I guess we need more info from 1951.

 

[Fast14riot]

Might be a little fiddly with a cast slug, but for measuring 5 bolt wheel lug patterns measure from one bolt to an adjacent bolt and multiply by 1.701 to get diameter. May be able to measure from top of one groove to the top of the next one?

 

[butchlambert]

Wouldn't be hard for me as I have pin gauges, vee blocks, indicators, and so forth. If I had a cast or slug I would spin it in the vee block and note the indicator reading. Now go to the pin gauges and find one that matches the cast or plug's indicated OD. Get your trusty mic and measure your pin if it isn't marked. That will give you your groove diameter.

 

[Walt Krafft]

To measure it directly you need a micrometer with a V.

 

[JSH]

V gauge for odd number lands

 

[Will Henry]

You use a 72 degree v-block and use it to establish the length of the chord. From that you can calculate the circumference and diameter of your circle.
The easy way is to use the vee block to measure your slug then measure gauge pins in the same block until you get the same measurement.
To use the v-block, you set the slug in the block, resting on the lands (corresponding to the grooves in the barrel) and measure from the top of the block to the top of the slug. If the height of the block is precise, it is possible to determine the factor by which you can calculate diameter from this measurement. I could look that up or figure it out but it puts a strain on my brain so I'll just count on one of the engineer types on here to show off for us and tell us how.
For myself, I use the comparative measurement technique with the gauge pins and it's good enough for me. WH

 

[Alan Warner]

A CMM will do nicely.

 

[Bob3700]

A CMM will do nicely.

Alan,
I picked a CMM up at Harbor Freight for cheap!

 

[Alan Warner]

Make sure you qualify it off of known gaging standards. Most cmms are good to +,- A tenth unless its a zeiss or similar. If you got a ball standard with the machine, look at the cert it should have come with it.

 

[ebb]

Whats a CMM???

 

[tobnpr]

Someone explain to this guy that doesn't shoot cast boolits...
Why is it even necessary to try to determine the exact bore diameter?
Slugging the bore compresses the lead to the smallest groove diameter of the barrel.
Why doesn't simply miking the OD of the slug tell you what you need to know?

 

[paperpuncher]

Someone explain to this guy that doesn't shoot cast boolits...
Why is it even necessary to try to determine the exact bore diameter?
Slugging the bore compresses the lead to the smallest groove diameter of the barrel.
Why doesn't simply miking the OD of the slug tell you what you need to know?

OP is having difficulty measuring the od of the slug because of the odd groove configuration It has a land opposite the groove so when an attempt is made to measure via conventional mic or caliper the full diameter is not realized I specialized mic or other means are need to get the diameter. Diameter is required to size cast bullets to fit the bore

 

[Dusty Stevens]

Reason #54 to stay away from odd grooved barrels

 

[Bob3700]

Lots of 5R bbls out there willing their fair share of matches.