09-11-2013, 07:45 PM
Several things can be manipulated within the bore depending on what the designer of the button considers important. Bore diameter, bore area and land to groove ratio and all combinations of those to meet the need.
I heard where some famous or maybe infamous project lead had designed a button for a new hopeful military cartridge a few years ago. He wanted more bore area so he simply made the groove diameter larger than the bullet diameter(more than needed for stretch and rebound). If the button maker hadn't caught it the bullets would have rattled down the bore and they would have had blow by at least until carbon built up.
Just an if. If someone designed a button without knowing the stretch and rebound of the barrel material the groove could end up smaller than needed. A little smaller could help accuracy, a lot smaller could increase pressure more than wanted.
A button too large or no stress relief could result in a big sloppy bore, slower velocity with less pressure and poor accuracy.
An air gauge would not map the bore but it could be used to compare the groove diameter between 2 barrels if in this case the 5R rifling was close enough to use the same air gauge.
I heard where some famous or maybe infamous project lead had designed a button for a new hopeful military cartridge a few years ago. He wanted more bore area so he simply made the groove diameter larger than the bullet diameter(more than needed for stretch and rebound). If the button maker hadn't caught it the bullets would have rattled down the bore and they would have had blow by at least until carbon built up.
Just an if. If someone designed a button without knowing the stretch and rebound of the barrel material the groove could end up smaller than needed. A little smaller could help accuracy, a lot smaller could increase pressure more than wanted.
A button too large or no stress relief could result in a big sloppy bore, slower velocity with less pressure and poor accuracy.
An air gauge would not map the bore but it could be used to compare the groove diameter between 2 barrels if in this case the 5R rifling was close enough to use the same air gauge.