Help with bullet diameter measurement.

[kopperl]

I have decided to keep my 297/250 Rook stock. Measured the bore today and came up with .247 dia and eight grooves.
Someone posted that five or more grooves would give a false reading.
Would someone explain and tell me how to proceed.

Thanks,
Bill

[country gent]

As far as measuring Odd number of lands and grooves (3,5,7) are hard to measure as no two grooves are oposite each other. even number are accross from each other so easier to measure.

[GhostHawk]

You say you measured the bore, tops of the land on one side to the top of the land on the other side?

Now you need to measure the "Grooves"

Read the sticky on slugging a bore.
(Think taking a slightly larger than the bore pure lead fishing sinker, driving it into the barrel, and all the way through.
Then measure the slug, 1-2 thousandths bigger than that is your ideal mold size(

Good luck!

[gpidaho]

Bill: Look through your (and friends) sizing dies to see if you have anything close to groove dia. size a boolit and do a comparative measurement should get you "close enough" GP

[kopperl]

Thanks, appreciate the help.

[Mk42gunner]

Bill,

Here is a thread I started about Vee blocks to properly measure odd numbered rifling: https://www.google.com/url?q=http://castboolits.gunloads.com/showthread.php%3F239450-Vee-block-for-measuring-odd-numberof-lands-and-grooves&sa=U&ei=uK5CVKDSBeGr8gHSkIDwCQ&ved=0CAYQFjAA&client=internal-uds-cse&usg=AFQjCNGxbaGcAAAUUuQpCGi6RNfe05TVhg

However, you don't need that. You have eight lands and groves if I am reading your post correctly, (it only took me two tries this time). Just measure across the slug for groove diameter.

As I see it, you have two basic choices for a mold: one, find one of the relatively rare molds meant for the .25 ACP, which should throw a boolit somewhere around 50 grains IIRC.
Or two, have a custom mold made to your specs by someone that does .25 caliber.

I have been interested in Rook rifles for a long time, I just never found one when I had the spendable cash.

Robert