For those who might not have seen this before.
Jackie Schmidt
Try This
Forget about the "Gunsmith" thing for a minute and look at this strictly from a Machinist viewpoint.
If bores were truly straight, all of this would be a moot point, because any 1st year apprentice can indict two points.
Since bores are not "straight", (in fact, they are not even "curved', they have "kinks" in them), you have no choice but to true two points and then some way get a third point running true with those two points. From a machinist standpoint, the only way to do this is to single point bore that "third point", thus establishing three points that run dead true with the machines bearings, (ie, "true").
By establishing the muzzle end true, and then establishing a point in the bore's area that will represent the first thing that the bullet "sees" as it leaves the case neck, then single point boring the chamber so it runs dead true with these two points, you will have no problem establishing a chamber that is "true" with the barrel's ID. That is, true with the original two indicated points, heck, one inch further from those two points may show as much as .001 run out. There is nothing you can do about this, because the bore is not even straight with its own self.
How many of you actually check everything after you finish a chamber. I do. I have written this before, but for those that have not been around that long, I will repeat the process.
After you have finished your entire chamber job, and before you remove the barrel from the final set-up, here is how you check your work.
Take your long stylus indicator and reach into the bore just a fraction further than where the lead angle ends. Indicate the lands and grooves, and see how much variation you get. Then, move the indicator back until you are on the actual tapered lead, (the last thing the reamer cut). Take a reading. Then, move the indicator back to the neck portion of the chamber, then to the body of the chamber, front and back.
Then, put your lathe in what ever thread you cut, and kick the half nut in. Place the ball stylus of the indicator in the V's of the thread, roll the chuck until all slack is out and the carriage is advancing. Record the indicator reading. Then place the stylus on the shoulder of the tenon, and record any run out there.
If you get more than .0002 to .0003 on any of these, you are inducing run out somewhere in your set-up. And, until you actually check your work, and see, you are simply relying on your set-up to be correct.
Of course, I am well aware that many of the lathes that Gunsmiths and Hobbyist use for their work are not even capable of producing this type of accuracy. Which leads us to this point. How accurate does all of this have to be? I have checked barrels done by others, and in my opinion, they never actually check their finished job because I get quite a bit of run out when checking the various fits against the others. These barrels shot great.
Sorry, but I tend to look at everything from a Machinist viewpoint. In my world, the only thing that counts is the finished job. Of course, you do have to have a means of performing operations that are within the capabilities of your shop, and of course, your budget And, you have to be willing to check your set-ups and correct any procedures that will cause the finished piece to be less than satisfactory when subjected to final inspection.
In my opinion, many of our "gunsmiths", and "machinist" in general, are simply "painting by the numbers". Change any part of the equation, and they have no way of knowing how to modify the operation to correct the flaws that can show up in the final inspection........Jackie
Last edited by Jackie Schmidt; 02-07-2011 at 09:29 AM.
