Fitch,
How many barrels have you chambered and shot?
None yet. But that doesn't invalidate what I wrote.
I hesitated to reply the first time, but this remember your geometry one line BINGO! thing got to me because it is not the whole story. More than one line can be defined which I think I pretty clearly demonstrated.
This is a forum for dialog on the subject of accuracy, shooting, and related stuff. Differing points of view should be addressed logically. If everybody just agrees that what's been done a lot is the best way because it's been done a lot, it really limits the opportunities to advance the science.
I don't think the one line, two line, thing is like the big enders little enders argument in Gulliver's Travels. There are underlying physical principles here that are being applied differently.
I've been right a lot of times in my life when nobody agreed with me at the start. I once have about every body in the NASA electrical establishment and all of those at Boeing thinking I was nuts, but they came around eventually. And I've been shown where I was wrong, more than once, in which case it was me that did the coming around. No problem. All I want is to understand the theoretically correct approach - it's hard to work for improvement if one doesn't have a clear understanding of the underlying physics. Folks may not do it that way, but that doesn't change the physics of the situation.
In the interest of completeness, and in the search for understanding, I just had to bring up the other point of view. I didn't say a person can't have an accurate barrel blindly centering the bore at throat and crown regardless of anything else, folks have done that. In fact I acknowledge that it has happened a lot. I just don't think it is the best way, and I stated (clearly I hope) the theory behind my thinking. I haven't heard a logical argument that says the one line approach is better in theory, just that it is done a lot, everybody does it, and that makes it better. That isn't an argument that I tend to give a lot of credence to.
That said, the two line approach may not be all that much better, especially if one is working with barrels that happen to have really straight bores near the muzzle and breech. As bores get straighter and straighter the performance (group size) of the barrels will converge. If the bores are perfectly straight, there is no difference at all.
One of these days if you shoot very much and find for some reason in a match that a barrel doesn't shoot,. Instead of saying I'll do the best I can, you will put another barrel on.
That's what got me into this to begin with. The 9" twist .22-250 Rem barrel on my LRPV is wearing out - it's still good enough to take out a ground hog at 300 yards, but it isn't as competitive at matches as it was. I want to put on a new barrel. The new barrel is going to be chambered in .243Win. I already have dies for .243 WIN. I'm going to rebarrel my sporter that is already chambered in .243 because it shoots 1+ MOA groups and I'd like it to do better. I may set back and rechamber the .22-250 barrel and save it for GH hunting.
[/QUOTE]Chambering the way that you are advocating may put your point of aim off far enough to be off the target board. [/QUOTE]
I'm no stranger to barrels pointing in odd places. When it was new, my factory stock Savage LRPV shot quarter minute groups 12 minutes left of being aligned with the receiver - I needed to use windage adjustable mounts to get it centered enough to make the scope useful out to 500 meters which is as far as I've shot it so far. Windage changes with range changes in no-wind conditions. I'm going to recrown it and if I rechamber it I'll see if I can chamber it so it points up.
My friends stock BVSS (also a .22-250) shot so far to the right his scope ran out of clicks with the bullet still off the 14" wide paper. The scope had 28 minutes of windage, the paper was 14" wide. It was off the paper to the right when he shot at the left edge with the scope all the way left. Near as we could tell it was 28" right out of the box. He returned it to Savage, they apparently rotated the barrel, when it came back it shot more centered (8 minutes right) and a LOT higher. He was better able to deal with the up than the right. I'd be surprised if I did worse than that.
The way Savage chambers barrels it is a wonder they shoot as well as they do.
I plan to put the deviation up in the vertical plane, which will probably take some practice to do predictably.
At 200 yards. do you have enough skill and guts to get it on paper and shoot a competitive group?
At the range where I shoot, yes. I have shot in 4 matches, all last summer. I finished 2nd in light custom in my first match, won the next two in factory class shooting 75g bullets out of my .22-250. The competition included targets at 200, 300, and 500 meters. On a national scale, not competative, no even close. Though once I get a rifle built and some more experience I may journey up to Williamsport to take their 1000 yard shooting school. It's only about 2 hours north of me.
I'm just starting. My problem is reading the wind, not the rifle. I was shooting with what I bought to be a varmint hunting rifle with an inexpensive 6-24x40 scope on it. I had no thought of getting into competition with it, but it was serious fun and I got hooked! I love it when the holes appear where I'm aiming!
Now if you are in this to be with the guys and shoot OK every once in a while, your way will work.
As Bill Leeper said, if it is off a lot, it just needs to be sent back.
Fitch, If you have a relatively straight barrel, how much trouble will you be in if you indicate the crown and the throat at the same time.
I wrote that as the bore gets straighter, the difference between the approaches gets smaller and smaller. Note, that if the bore is really really straight, the two line approach ends up with the same result as the one line throat muzzle approach. If they are a bit different, then in theory, the two line approach results in smaller groups because of improved symmetry of interaction between the bullet and the bore, although they may be located in a different place on the paper before the sights are adjusted.
I want to optimize my chambering efforts to get smaller groups, sights are adjustable.
The comparison is a hard thing to test. There are so many variables that isolating one thing to parametrically characterize it's effect is nearly impossible for some one not involved in a government funded study. Certainly not possible for me to do it. I need to get that book on accuracy factors and read it. That's high on my list.
[/QUOTE]If you indicate the throat, drill and taper bore before reaming and then ream, do you think you will be less straight than Gordy's way? Don't forget that Gordy's range rod will have the .0002 clearence between the bushing and the rod and you will have at least an additional .0002 clearence between the bushing and the top of the lands. Your tolerance could be stacking already.[/QUOTE]
I wondered about that. Had the following thoughts.
To start with, the Grizzly rod bushing fits tighter in the bore than the end of a DTI. I realize the tip of the DTI presses against one side of the bore so what is being measured is the relative location of one side of the bore as the barrel is rotated. The bushing on the Grizzly rod will press against one side of the bore just like the tip of the DTI. The bushing is larger in diameter so it should move relatively smoothly rolling over the lands instead of dropping into them. The bushing will be centering the tops of the lands. I don't know if the DTI tip will always get to the bottom of the grooves or not. Probably will in most cases - in which case one has a choice between centering the top of the lands or the bottom of the grooves.
The reamer pilot centers on the top of the lands so there might be some benefit to using that data.
The question is, now sensitive will the measurement system be? That is, if the bushing moves .0002", what will the DTI that is measuring rod displacement indicate?
Assuming for a moment that the range rod is 13" long, 12" sticking out from the tailstock chuck, and that the DTI presses against it 1" from end and 3" from the end. With this geometry, if the end of the bushing moves .00020", the DTI will move .00018" if it is 1" from the bushing. If the bushing moves .0002" the DTI will move .00015" if it is 3" from the bushing. It's more a matter of sensitivity than anything else.
If a DTI has been fitted with a longer than normal probe tip, like I've read that some folks do, the sensitivity is reduce by the ratio of the original tip length divided by the new tip length. The Grizzly rod is more accurate if a DTI has been fitted with a noticably longer than normal probe tip, slightly less accurate if the DTI was calibrated with the long tip.
I think it is pretty much a wash.
[/QUOTE]All of this being said the real gunsmiths out there that do all the top notch work think all of this is a real funny thing to read. [/QUOTE]
Not all of them. But I don't see what that has to do with anything. If the whole world says 2+2=3 that doesn't make it right. It just means folks agree to something that isn't right. Physics isn't negotiable, it is what it is. One can make compromises in approach accepting the differences as negligable, but that doesn't change the underlying physics.
OK, how much do you think that I am giving away in alignment by indicating the crown, indicating the grooves at the throat, drilling, reindicating the throat, taper boring, and reaming as against Gordy's method? Not much if any!
If the bores are straight, you are right, not much. I agree, the straighter the bores, the less you give away. What mystifies me is why you want to give away anything?
If the barrel is an elipse or a helix you won't gain anything.
Butch
OK, this last confused me. Elipse or helix? I'm not sure what geometry you are applying the ellipse or helix to. Bore cross section elliptical instead of round? Bore centerline describing a helical path down the barrel?
Thanks
Fitch
