Boyd Allen
Active member
Having studied the print for some time and spoken to Dave Kiff (its designer) at some length about it, I will take the liberty of pointing out a couple of things that may not have jumped out upon first inspection.
Of course the parallel section (.2435 dia.) is pretty standard except that at .111 it is longer than any other 6PPC drawing than I have seen.
The tapered section in front of it, that is .200 long has a taper of .53 degree per side (31'-48", calculated from the dimensions), and the smaller dimension at its front takes that part of the cut up to about half the height of the lands on a barrel with a .237 bore.
Forward of that section, the lands are cut at the more common 1.5 degree angle.
For the person that wanted to know about the .233 dimension, it should be remembered that this is a reamer print, which corresponds to the chamber dimensions in those areas where the reamer cuts, but may have dimension for the reamer grinder that a chamber print would not. In this case it tells him what the diameter of the reamer is to be at the point where the degree and a half taper ends.
Looking at the middle section again....it starts with a cut that cleans off the lands at its big end and if we do a little calculation the lands are likely to start to show about .026 into that taper, assuming a groove diameter of .243. So, about .137 in front of where the 45 degree transition from the neck part of the chamber ends, the bottom of the lands start to show, and the effective leade angle at that point is about a half of a degree.
My conversation with Dave had started with the intent of just ordering a throating reamer but he told me that all of the dimensions had been designed to work together (meaning that the long parallel section was part of the design and that shortening it up to put more bullet in the case neck might change performance)so I took his advice and ordered (for a friend) the chamber reamer. It is supposed to be here today, and I imagine that by tomorrow that a chamber will have been cut, and wind permitting, testing begun. We have some of the 65 gr. BTs as well as some Columns.
Of course the parallel section (.2435 dia.) is pretty standard except that at .111 it is longer than any other 6PPC drawing than I have seen.
The tapered section in front of it, that is .200 long has a taper of .53 degree per side (31'-48", calculated from the dimensions), and the smaller dimension at its front takes that part of the cut up to about half the height of the lands on a barrel with a .237 bore.
Forward of that section, the lands are cut at the more common 1.5 degree angle.
For the person that wanted to know about the .233 dimension, it should be remembered that this is a reamer print, which corresponds to the chamber dimensions in those areas where the reamer cuts, but may have dimension for the reamer grinder that a chamber print would not. In this case it tells him what the diameter of the reamer is to be at the point where the degree and a half taper ends.
Looking at the middle section again....it starts with a cut that cleans off the lands at its big end and if we do a little calculation the lands are likely to start to show about .026 into that taper, assuming a groove diameter of .243. So, about .137 in front of where the 45 degree transition from the neck part of the chamber ends, the bottom of the lands start to show, and the effective leade angle at that point is about a half of a degree.
My conversation with Dave had started with the intent of just ordering a throating reamer but he told me that all of the dimensions had been designed to work together (meaning that the long parallel section was part of the design and that shortening it up to put more bullet in the case neck might change performance)so I took his advice and ordered (for a friend) the chamber reamer. It is supposed to be here today, and I imagine that by tomorrow that a chamber will have been cut, and wind permitting, testing begun. We have some of the 65 gr. BTs as well as some Columns.
