First thing -- I admit I have a strange & peculiar affliction about words. In this case, it is the word "blueprinting" when used to refer to truing an action.
Blueprinting refers to a set of dimensional specifications. If a single number is used on the blueprint, the quality control department has to allow some "dimensional generosity," or nothing would get out the door.
One is tempted to say that "dimensional generosity" means there is a lack of precision, but the truth is there is always a certain amount of "dimensional generosity" -- nothing is perfect. But benchrest & some other shooters have found that the dimensional variations allowed by the large manufacturers are too generous, that is, they can shoot, on target, using enough rounds to be statistically significant, the difference between what the factory allows and what can be achieved with a custom (small manufacturer) action that allows far less variation.
So, what can you do to a factory action to tighten up the tolerances. If it is outside the "blueprint" specifications, you gonna add material back? No. You can never get it back down to the "blueprint" specifications. What you can do is take off more material, "truing" it to certain reference points. Depending on how much material is taken off, the resulting action may no longer take factory parts, esp. barrels.
There is a second issue. Suppose there are 10 dimensional things in an action that have a significant affect on the accuracy of a rifle built on that action. Suppose you fix one or two of them. Has that helped? Not much. There is an old formula that I first ran into regarding the resolution of a camera lens. After discussing the various compromises in the lens itself, the author made the point that the resolution of the system -- that is, the photographic prints you make, depends on the lens, its fit in the camera, how the film is held in the camera, how the film is processed (the negative), the enlargement system (if used) and the photographic printing paper and it's development. If you're "looking at pictures" (if you are shooting targets rather than writing articles), it is the total system that matters. BTW, there are equivalents with digital images -- when the laser-printer manufacturer's marketing department says "1200 dpi resolution," did you really think they were referring to the whole system?
So.
1/R(total) = 1/R(1) + 1/R(2) + 1/R(3) + . . . +1/R
With 10 variables, drop any single or pair of R's, and see the effect on R(total). It's not much.
Perhaps that explains why the "smith" who "trued" an action and, using "the same barrel on a factory action" found no difference.
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I have to allow I didn't read the Boatright article. Since the late 1990s, when I renew my IBS membership each year, I write "No Precison Shooting" on the renewal form. Now my blood pressure is 110/60.
There is a strange interplay between theory and practice. It is an old adage that if you don't see it on paper, it doesn't matter. I hold to that. There is an equal adage that if something can be proven theoretically, it is important. I hold to that, too.
The two don't always meet. Sometimes, (my opinion only) as in the case of Boatright's earlier article on forcing cone angle versus bullet ogive, the theory rests on a couple of faulty assumptions. Given the assumptions, the conclusion is valid. But if the what is taken for granted is wrong, it's all smelly gas.
The other case is where the theory could be right, but will only hold if something else is done. There is another old adage: Do one thing at a time, then test it. If nothing changes, it doesn't matter. That is not usually true. Go back to the resolution formula. With something new, some new potential improvement, the problem comes up when there were two things that needed work but you only found one of them. Your conclusion that it wasn't important could be wrong, it needed something else to show.
Trivial example: you face off the front of the receiver. It was .002 out. Now you reassemble the rifle, using the same old recoil lug between the barrel and the receiver. It is .005 out. Would you be surprised if you couldn't shoot the difference between the faced off receiver and the stock receiver? Suppose the the two parts were each off in such a way to partially compensate, and the faced-off receiver shot worse. Is it then a bad modification?
Is this contentious enough for you?
