I look at reamer prints and see two dimensions that are what I would think is freebore as I understand it. One is from the end of the case portion of the chamber to a point in in the bore before where the rifling begins. Then there is a small chamfer that goes from the case neck portion to the grove diameter. The second measurement goes from the front of the bevel to the same point of the first measurement I mentioned. I see another measurement that is from the boltface to the line that these other measurements stop at, is labeled as "LEAD". I see another measurement from the boltface to where the rifling seems to begin, and this one is marked "THROAT". Looking at these measurements how do I determine what the freebore is? Buy maybe my understanding of freebore is incorrect. Freebore as I understand it is the measurement from the end of the case portion of the chamber to the origin of the rifling. Is this corrrect?
Understanding reamer prints-freebore.
- Thread starter Larry M
- Start date
jackie schmidt
New member
Larry
Sometimes it depends on the reamer design.
You are correct in that the real important dimension is the one from the bolt face to where the lands actually begin. That takes into consideration the bevel, the actual trim to length, or any other dimension that might be incorperated in the drawing.
That is one more thing I like about my "zero" freebore concept. Since it isn't there, I don't have to worry about it's diameter, or it's length......jackie
Sometimes it depends on the reamer design.
You are correct in that the real important dimension is the one from the bolt face to where the lands actually begin. That takes into consideration the bevel, the actual trim to length, or any other dimension that might be incorperated in the drawing.
That is one more thing I like about my "zero" freebore concept. Since it isn't there, I don't have to worry about it's diameter, or it's length......jackie
Here is a print of a JGS reamer with the freebore clearly delineated at .2433 diameter and .045 long.
http://eddavis3.homestead.com/files/6PPC_Davis.jpg
Note that by "clearly delineated" I do NOT mean clearly or concisely labeled! The term "lead" or "leade" as pertains to chambers cannot be found in any but obscure dictionaries with the only related reference being that a "leade" is a term for a smoothly tapered beach, "the transition area between the water and the vegetated shoreline".
In this print the "freebore" is the section from the end of the chamber ( 1.5344 ) to the blue line marked "lead". The designation "u & v" under the freebore dimension is unclear to me.
Another way to look at it, the freebore is the parallel section marked as .2433 diameter which occurs between the end of the chamber and the beginning of the tapered "leade" of the rifling lands.
hth
al
http://eddavis3.homestead.com/files/6PPC_Davis.jpg
Note that by "clearly delineated" I do NOT mean clearly or concisely labeled! The term "lead" or "leade" as pertains to chambers cannot be found in any but obscure dictionaries with the only related reference being that a "leade" is a term for a smoothly tapered beach, "the transition area between the water and the vegetated shoreline".
In this print the "freebore" is the section from the end of the chamber ( 1.5344 ) to the blue line marked "lead". The designation "u & v" under the freebore dimension is unclear to me.
Another way to look at it, the freebore is the parallel section marked as .2433 diameter which occurs between the end of the chamber and the beginning of the tapered "leade" of the rifling lands.
hth
al
JGS prints
It's my understanding that on JGS prints, the freebore length is shown as the dimension in the U & V box. Subtracting the 'U' dimension from the 'V' dimension will give the freebore length as well. That's what I have in my notes and dwgs. and I believe this was confirmed by a call to JGS in the not too distant past.
Chino69
It's my understanding that on JGS prints, the freebore length is shown as the dimension in the U & V box. Subtracting the 'U' dimension from the 'V' dimension will give the freebore length as well. That's what I have in my notes and dwgs. and I believe this was confirmed by a call to JGS in the not too distant past.
Chino69
PT & G prints
I'm looking at a PT & G print and, if not designated, look for the datum line that says 'lead' which is 'V' on my print as well as JGS prints. The PT & G print I'm looking at has a dimension listed as 'U' which is from the bolt face to the datum line at the very end of the neck/bore diameter transition. You should see the 45 degree angle designation. Subtract the smaller dimension from the larger and you'll arrive at the freebore. I hope this helps.
Chino69
I'm looking at a PT & G print and, if not designated, look for the datum line that says 'lead' which is 'V' on my print as well as JGS prints. The PT & G print I'm looking at has a dimension listed as 'U' which is from the bolt face to the datum line at the very end of the neck/bore diameter transition. You should see the 45 degree angle designation. Subtract the smaller dimension from the larger and you'll arrive at the freebore. I hope this helps.
Chino69