Quote:
Originally Posted by lclund1946
There is much confusion about the terms Leade, freebore and throat. Your description of throat is actually describing the neck area of the chamber which is typically 0.010" longer than Maximum case trim length. If you look at a Pacific Tool & Guage reamer print you will see that this then transitions at a 45 degree angle down to the Lead which is the area that the lands are cut out typically 0.0005", or a bit more, over the caliber diameter. PT&G drawings show Freebore as the length of the Lead or area where there is no lands (rifling). Ahead of the Leade is the throat which is cut at an angle to the diameter of the Freebore area, which can range form less than 1 degree to over 3 degrees, cutting out the lands and forming the cone that you describe. Bullet Jump to the Lands is often called freebore but is actually a combination of seating depth, freebore and throat angle. The bullet does not contact the Lead so no copper is transferred until it reaches the throat which is where Kreiger talks about cooper transferring to reamer marks. These usually disappear after about 3 shoot and cleans on a good hand lapped barrel after which copper transfer becomes very minimal and the barrel would be classed as broke in.
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All good , but my question was referring to polishing a chamber, not lengthening a throat or cleaning up the leade . AFIK , a chamber is a chamber and ends pretty much at the case mouth. It has specific SAAMI or custom specs peculiar to each different cartridge. The throat and leade are actually different operations that can have arbitrary dimensions or angles and are actually part of the bore. Apart from that, I believe the bullet does contact the leade as it enters the bore (thus the angle) and
after it crosses the threshold of the freebore dimension ( throat.) If I'm wrong about all this, I'm sure I will be corrected in short order.
What do you suggest regarding chamber polishing .. good idea, or not so good ?