The Firing Line Forums - View Single Post - chambering / throating for accuracy... with both jacketed & cast bullets...

Harry Bonar · September 29, 2008, 06:13 PM

Sir;
Art Alphin of A-Square Co. inc. throats his rifles with a paralel throat.
If it is a 30 cal. he makes a "paralel" throat .0005 or .001 larger than the bullet (30 cal would be .3085 or .309 as a paralel throat for a distance and then makes the classic rifling groove dia. normal throat at the end of the "paralel" throat.
This serves several functions; first, it is not "freeboring." It gives the bullet (jacketed or cast) a good start in life and then enters the classic "throat" into the rifling.
For instance, you can load long bullets without concern over length. Second, it aligns the bullet precisely into the bore. In a 308 or a an 8mm. bullet the bullet has a good start into the rifling, contrary to the regular throat in which there will be some misalignment.
In the Lyman 311296 buillet the front of bore diameter (.300) while back at the driving bands it's 308 or .309 (depending on how you would size it).
I'm concerned about the rolling block action!
Their construction offers (while normal and safe for some cartridges) no upper support to the breech block! ALL of them have a stretch - they do not support the case 360 degrees! Not condusive to good accuracy. Case walls MUST grip the chamber therefore to reduce "case head thrust" on this action. Personally, I'd relagate rolling block actions to black powder cartridges.
However, this "paralel" throating would solve your problem.
Harry B.

September 29, 2008, 06:13 PM	#2
Harry Bonar Senior Member Join Date: December 5, 2004 Location: In the Vincent, Ohio general area. Posts: 1,804	chambering and throating Sir; Art Alphin of A-Square Co. inc. throats his rifles with a paralel throat. If it is a 30 cal. he makes a "paralel" throat .0005 or .001 larger than the bullet (30 cal would be .3085 or .309 as a paralel throat for a distance and then makes the classic rifling groove dia. normal throat at the end of the "paralel" throat. This serves several functions; first, it is not "freeboring." It gives the bullet (jacketed or cast) a good start in life and then enters the classic "throat" into the rifling. For instance, you can load long bullets without concern over length. Second, it aligns the bullet precisely into the bore. In a 308 or a an 8mm. bullet the bullet has a good start into the rifling, contrary to the regular throat in which there will be some misalignment. In the Lyman 311296 buillet the front of bore diameter (.300) while back at the driving bands it's 308 or .309 (depending on how you would size it). I'm concerned about the rolling block action! Their construction offers (while normal and safe for some cartridges) no upper support to the breech block! ALL of them have a stretch - they do not support the case 360 degrees! Not condusive to good accuracy. Case walls MUST grip the chamber therefore to reduce "case head thrust" on this action. Personally, I'd relagate rolling block actions to black powder cartridges. However, this "paralel" throating would solve your problem. Harry B.