Calfee indexing, correct interpretation?

[Don]

Over the years I have viewed tens of thousands of competitive target groups and I think I have a pretty good feel good gun grouping.

While reviewing a Bill Calfee article and target photos about barrel indexing, PS October 2007, Bill noted that the difference in the target group aggregate sizes for the different clocking positions varied from .232" to .201", and was not enough of a difference to determine a preferred position, with the good possibility that if the test were repeated, different aggregates could have changed for each clocking position.

When I saw the targets that he was referring too (attachment), I immediately said to myself, that the 270 degree targets of the bottom row were superior in both shape and size, and that I definitely would have further explored the 270 degree clocking position with that particular barrel. The groups were consistent with very little hanging out from the round formation of the grouping, unlike the others, which is always a good sign.

Group interpretation, I feel, is particularly important in CF accuracy developement, where barrel life is short, and only limited amount of developement and experimentation can be done before competitive accuracy life disappears.

Also, when accuracy begins to approach the .1 levels, even a .030" group size difference along with group shape interpretation can make for a considerable improvement.

My intent is not to criticize Bill in any way, but question whether we are missing some important gains because we are looking for the singular "holy grail", when perhaps it will require several more small incremental gains before we truly reach consistent single hole groups..............Don

 

[jackie schmidt]

Don

First, If that is a 22 caliber, there are definetally groups on those pages that are bigger than .223.
I agree with you. The bottom set of groups are the kind of groups I look for.
As for indexing, I really don't think it has anything to do with the amount of curve, (actually runnout), that a barrel exibits. It probably has more to do with some entangible that we have little clue about. In short, it might just like a certain position better than another. At the level of accuracy that we are achieving, sometimes little things can make a barrell perform better, even without us knowing what.
I am getting ready to chamber up a new Rail Gun Barrel. Maybe I could do a "indexing" experiment with it. Do you think the action will mind being shot "upside-down" and "side ways"??........jackie

 

[Don]

First, If that is a 22 caliber, there are definetally groups on those pages that are bigger than .223.
I agree with you. The bottom set of groups are the kind of groups I look for.
As for indexing, I really don't think it has anything to do with the amount of curve, (actually runnout), that a barrel exibits. It probably has more to do with some entangible that we have little clue about. In short, it might just like a certain position better than another. At the level of accuracy that we are achieving, sometimes little things can make a barrell perform better, even without us knowing what.
I am getting ready to chamber up a new Rail Gun Barrel. Maybe I could do a "indexing" experiment with it. Do you think the action will mind being shot "upside-down" and "side ways"??........jackie

Hi Jackie,

I think the group sizes that Bill stated were aggregates for each row of targets that in turn represented the different clocking positions, since these were aggregate group sizes I am sure some were larger than .230" and others in the .1s, to pull the aggregate size down to less than .230".

As for spinning your barrelled/action in the barrel block on your railgun, I do that very same thing with one of my specially built Jay Young rail tops that doesnt have a trigger gaurd built into the plate, and has adjustable barrel block positioning holes front and back. As long as your trigger assembly and bolt handle can clear everything on the top plate and the scope, than you should be good to go.

Warning though, you will experience 4 distinct paculiarities;

1. Difficulty in loading a round in certain clocking positions.

2. Pulling the trigger in certain clocking positions, especially with the trigger at 12 oclock, between your eyeball and the scope.

3. Camming the bolt handle in certain positions.

4. Answering questions from fellow shooters as to what the heck you are doing.

Don

 

[RvA]

Jackie,

The 0, 90, 180, and 270 are starting points, you can refine the group further once you find where to go.

Best,

Roger

 

[jackie schmidt]

Don

Yeh, I like that last one. Many would be thinking that I finally confirmed what they have suspected, that I was just a little nuts.
Since there is nothing about the design of my Rail that hinders me from doing this, it would be a neat exercise.
What would complete it is this. If I did happen to find a position that the barrel liked more than other, I would bring the barreled action to the shop, set the shoulder back the correct amount, so that the action sits correct, and go try again.
I can't promise anything, we are now into the shooting season. But I do have the means, and the facility to do this, so let me think about it.
And of course, there is always the reality of testing at Tomball. This time of year, we tend to have two conditions. Wind, and more wind. Even with the best flag set-up, and the utmost in patience, Demons still lurk.
Even though I am not much on tunnel testing, Gene Beggs' facility would be great for this exercise .....jackie

 

[Kathy]

Friend Don:

Friend Don:

In a magazine article one only has so much room to show stuff......My barrel indexing experiment took two long articles.......

When I ran the group tests with the barrel I named "Pierce Arrow" I only showed one set of targets....I acutally ran the test four times....A different indexing position had the best looking run on each test....

I actually took the best "looking" target to publish in the article.

After I submitted the article, and had time, I machined two more spacers, each .007", or withing a tenth or two of that.....I ran the test with Pierce Arrow using the original spacer rings plus the new .007" rings which put me in indexing positions in between the four 90 degree positions.....I even made up two .010" shims to place behind the firing pin spring in the Turbo breech bolt, to pre load the firing pin spring so I could maintain uniform ignition for the 4 new indexing positions...

I did this further test because even though I could do nothing to make any of the three barrels shoot any different, in any of the 90 degree indexing positions, I figured I may have missed something....nothing changed.

My friend, if I thought I could gain anything, I mean anything, by indexing my barrels, I'd figure a way to do it.....

Don, the only way I could get any of those barrels to shoot any better was when I would turn the whole action up-side-down, in my machine rest....this of course placed the firing pin at 6:00 and the barrels would always shoot better like this......

It's a free country.....if folks want to index barrels, that's cool...

Bill Calfee has done his last barrel indexing.....

Your friend, Bill Calfee

 

[Don]

Friend Don:

In a magazine article one only has so much room to show stuff......My barrel indexing experiment took two long articles.......

When I ran the group tests with the barrel I named "Pierce Arrow" I only showed one set of targets....I acutally ran the test four times....A different indexing position had the best looking run on each test....

I actually took the best "looking" target to publish in the article.

After I submitted the article, and had time, I machined two more spacers, each .007", or withing a tenth or two of that.....I ran the test with Pierce Arrow using the original spacer rings plus the new .007" rings which put me in indexing positions in between the four 90 degree positions.....I even made up two .010" shims to place behind the firing pin spring in the Turbo breech bolt, to pre load the firing pin spring so I could maintain uniform ignition for the 4 new indexing positions...

I did this further test because even though I could do nothing to make any of the three barrels shoot any different, in any of the 90 degree indexing positions, I figured I may have missed something....nothing changed.

My friend, if I thought I could gain anything, I mean anything, by indexing my barrels, I'd figure a way to do it.....

Don, the only way I could get any of those barrels to shoot any better was when I would turn the whole action up-side-down, in my machine rest....this of course placed the firing pin at 6:00 and the barrels would always shoot better like this......

It's a free country.....if folks want to index barrels, that's cool...

Bill Calfee has done his last barrel indexing.....

Your friend, Bill Calfee

Bill, I fully understand your position, and goodness knows with the amount of time and effort that you put into this indexing project, I am sure that you are convinced in your conclusion.

Even with my less than thorough method of spinning a barrelled/action in a railgun barrel block, I am coming up with very similar results as yours.

Even so, I will probably continue to index test some barrels with certain characteristics to futher determine the effects of indexing in those situations................Don