Copper Won't Go Away

[Harvey]

Little surprised no one has mentioned Montana X-Treme Copper Killer. Wicked stuff.

[mehavey]

About a year ago I was doing a compare-and-contrast test with KG-12 and
Montanna Extreme in which I filled two small polyethylene sample
cups (about the size of condiment cups at McDonalds) with both solutions,
dropped a jacketed bullet in each, and set both on the window sill in the kitchen.

Came back an hour later to find the KG-12 had fullet etched the bullet surface.
On the other hand the Montanna extreme had eaten through the cup, emptied it
onto the window sill, and eaten half the paint across the entire sill.
(The bullet, however, was still pristine)

[ColColt]

Well, Nick-That stuff is absolutely great. I got both the Eliminator and KG-12 today and went through the regiment you lined out and now it's squeaky clean...literally. As I ran patches down the bore it squeaked. I was somewhat surprised when I got to the KG-2, after all the preceding cleaning, that the patch turned black. However, after about 5-6 dry patches it came out clean.

The Eliminator did a pretty good job of cleaning, better than the Sweet's or Wipe Out I tried before, and you could see the blue color on the patch but it didn't get it all. It took the KG-12 to "mop up" what the eliminator didn't get. No copper on the grooves or lands now. Most impressed. Hopefully at the range tomorrow this rifle may shoot a bit better. If not, it's passed up a good chance.

[tobnpr]

Thing is, often a rifle will shoot better once fouled with a small amount of copper that fills very minor machining imperfections. Yours, did not...

Note point of impact vs point of aim on the first cold bore shot, then subsequent ones when you get the range time.

I'd be surprised if much changes and suspect it's going to load up again. Small amounts of copper fouling initially should reduce fairly quickly as imperfections get smoothed out. As much as you say you're getting makes me think it's not going to be so cut and dried.

Good luck, hope I'm wrong

[Unclenick]

ColtColt,

Glad that worked for you. Eliminator is fast and pretty effective on light copper, but it just doesn't get the volume of copper KG-12 will, so, in that procedure, we're using the Eliminator to get carbon and as a color indicator more than as a copper remover.

Eliminator would also have removed the black from the KG-2. What that black is comprised of is very fine metal particles removed by the polish. They are so small they do not correspond to measurable levels of metal removal. You see the same thing with any abrasive cleaner or metal polish. It is not dirt or fouling.

Try this experiment: rub some steel with a small amount of the KG-2 on a patch until the patch is not really polishing any further. Repeat with the brass on a cartridge and repeat with the copper bullet jacket on a cartridge. Now hold all three patches in bright sunlight and when you find the right angle you'll see a little of the silver, brass, and copper reflection coming off the black, proving it is comprised of particles of the metals you polished.


Tobnpr,

The problem you get into is that metals have their highest coefficients of friction with themselves. So, if copper gilding metal sticks to steel under pressure, it will stick to other copper even more. That's how the build-ups happen. And even in guns that don't build copper up too quickly, if you leave them uncleaned long enough, accuracy eventually deteriorates as the copper build-up becomes excessive.

The idea of filling imperfections with copper has been around for a long time, but I'm hesitant to subscribe to it. I've shot several guns with bad pits in the middle of the bore that shot very well even when clean, so I'm not convinced a perfect bore surface explains accuracy concerns. Rather, I suspect what changes is the same thing that changes with powder fouling, and that is that increased reaction force from the added friction improves consistency of the powder burn, same as getting higher and more consistent start pressure will do. In the clean, rough bore, the friction is just changing too much from shot to shot at the beginning of fouling for that consistency to be good enough.

It should be possible to tell if that explanation holds. You'd expect lower velocity SD and higher average velocity from the fouled bore if it is. If you just take and track velocity reading from a clean bore all the way to accuracy deterioration, you could do a curve fit to velocity and take a running SD from the early rounds on and see how it changes with fouling.

[ColColt]

Apparently what I did last night helped at the range today. I was not getting consistent groups like this before and while it won't set the bench rest world on fire it's for sure better than last time.

The first shot from a totally clean and cold barrel was slightly to the left but others grouped in a .820" circle. The target on the right was after those five shots and a five minute wait, ran a dry patch through the barrel and noticed it was grey instead of black. Fired those five with about a two minute wait between shots. Group ran 1.164".



I put the270 away for 30-40 minutes to shoot my .222 and came back to it to fire this group with 130 gr Nosler Ballistic Tips...should have let well enough alone but shot two more which opened an otherwise superb three shot group. Even at that it was 1.158". All in all I was pleased with the groups knowing partly the rifle could have done even better without me. Not too shabby for a FW barrel and it 82 degrees.

[Unclenick]

Good to see it worked out.

The first shot having a different POI than subsequent shots is pretty normal. Without fouling you have lower net friction, so it doesn't build pressure as early in the bullet position in the bore and exits with somewhat longer barrel time. That can move you off the vibration sweet spot.

If you want to, try shooting a round robin where you have three targets. Put the first shot from the cold, clean barrel in the first target, the second in the second target and the third in the third target. Clean and cool the barrel and repeat until you have accumulated a group on each target that you can find the center of to see how the center moves as the barrel fouls.

Obviously, the more shots there are in each group, the more accurately their their mean position (group center) estimates what the average for an infinite number of identical rounds would be if the gun and shooter never wore out. When you are grouping well, rounds may go through existing holes, making the average hard distinguish. If you have that problem, but want a bigger sample size for each group, just shoot a modest group size, like three or five, as you already did, then put up a set of fresh targets and shoot another three groups the same way, and keep going on for as many more sets of targets as you want. You can then take the group centers for each of the first shot groups and average their result to get the average you would have had if all the first shots had been on the same target. This works just as long as they all have the same number of holes in them. The same may be done with all the second shot groups and with all the third shot groups.

[ColColt]

Marvelous idea. I never would have thought of that. I'm still at the stage of working with loads to hopefully end soon and will try that. Fantastic idea, Nick.

From what the past couple of range visits have proved on those first shots I think next time I'll just shoot a flyer into the bank on that first shot as that first one invariably goes sour anyway.

I noticed from these targets that the POI seems to be a bit higher than the last two range visits. Before they were in the grey area putting them mostly 3" high at 100 yards. This past time they were a bit higher with basically the same bullet weight and powder. The barrel floats so, not sure what happened there. All I did this time was to super clean the bore.

[Unclenick]

That copper constriction was probably raising peak pressure. Peak pressure occurs when the bullet is still in the first inch or two of the barrel, making acceleration higher in that early portion of the trip down the bore. That means the bullet is starting the rest of the trip down the bore going faster, so the barrel time is decreased. That can cause the bullet to exit the muzzle when it is at a different phase of its "vibration", so it may actually be pointing slightly lower.

The flyer in the bank is traditionally referred to as "The Fouling Shot". That also happens to be the name of the Cast Bullet Association's member publication.

The reason for the round robin test is twofold. One is that it simulates what a hunter with a clean cold gun will have happen when firing a shot in the field followed by two follow-up shots (that we all try not to need). Or it'll tell you how many clicks right windage you need to add after a fouling shot. It'll also tell you if you need more than one fouling shot. The amount of shift and whether or not you trust yourself to hold off to correct will tell you whether or not you want to foul your bore before taking it into the field.

The second purpose is to compare the group centers you get to a later group center fired after, say, ten or twenty shots. This is to see if the gun is still shifting that late. Target shooters frequently report needing up to ten shots for a gun to settle after changing powders. If your's is taking that kind of time, you'll want to know when and where it settled down. You may even decide to fire a larger number of round robin targets if it is still shifting, though my first impression from your photo is that your gun is not doing so significantly.

I've been using the On-Target software, and find it useful for finding group centers. The freeware version linked to at the bottom of this page works fine. In fact, I've never bought the paid version. I probably will, though, just because I find the program useful and want to encourage the author. It's not expensive.

[ColColt]

That's a great program but when I got to the "Define Group Holes" the circle was way too big. Instead of being caliber size, which I defined, it was three times that size. I'll have to work on that.

[Unclenick]

ColtColt,

You missed the Set Reference step. It's the icon with a diagonal line between two x's. You click that, then click at one end of a known length on the target (the gridlines are perfect for this) then click at the other end, then tell it how many inches that was between the two clicks. It will then scale all the holes and calculate distances between them correctly.

If you have a photo with some barrel distortion, like your last one, use gridlines nearest the group so you tend to compensate for the distortion. But if you stand further back (using optical telephoto is good) and keep the centerline of the camera lens square to the center of the target, you'll get the least of that. Your upper photos look better in this regard. Of course, a flatbed scanner is best for this and has no barrel distortion at all.

[ColColt]

I was watching the tutorial and went by that but, it doesn't show that step. When I tried to click on one of the intersections of the grid a box pops up for me to set the reference distance and doesn't allow me to set the other point. I'll have to work on this. I used the grid line closest to the holes.

I took that shot with a Nikon 60mm Micro Lens at f/14 from about waist high and target on the floor. I don't see the barrel distortion you're talking about. That would bow the vertical lines outward and I don't see that. The image was a tad crooked and I tried to straighten it up with my software but was off a bit.

[Unclenick]

Sorry, I misled you. I hadn't run the program since the end of last shooting season. You select the Set Reference icon and you get a little ruler an X near the top end. Put the X at one end of the known length, click and hold down the mouse button and drag the X until it's over the other end of the known distance, then let go of the left mouse button. A window will pop up asking you to fill in how many units that length was.

You're thinking of pincushion distortion. Barrel distortion actually bows parallel lines inward as you move away from the center of the image, same as the edges of the staves of a wooden whiskey barrel are wider in the middle and narrower at the heads. Barrel distortion is most exaggerated in a fisheye lens, which has very short focal length.

The choice of f stop will affect depth of field for better near-to-far focus range at larger f numbers, but won't affect these kinds of distortion. Only changing focal length affects that, with longer focal length giving you a flatter, less distorted image. There also used to be, more commonly, what are called flat field lenses. These were lenses built with a little bit of intensional pincushion distortion to compensate for barrel distortion, though that only works when the subject is a flat plane perpendicular to the lens axis. The are used mainly on copy cameras and on photographic enlargers.

Below, I took your photo and pasted it into a CAD program and superimposed a straight grid over it. At the top corners you can see the vertical lines of your grid don't match as they do at the bottom of the photo. That's the barrel distortion. It's not a lot. About 2% closing in on the ends, but just enough that if you want to keep comparing apples to apples it won't hurt to re-set the reference in the corners.

[ColColt]

Thanks, Nick. sometimes I have to led by the hand but got it figured out. That's a great, useful program I'll keep.

Barrel distortion actually bows parallel lines inward as you move away from the center of the image,

One of us has this barrel/pin cushion distortion backwards. Consider the barrel you mentioned. If you look at the sides of it, it bows out on the right and left sides. Pincushion, of course being the opposite, causes vertical lines to bow inward, especially lines like architecture, on the left and right sides of a photograph.

The reason those lines on the targets are out of whack is they are two separate targets just stapled to a piece of card board side by side and originally printed off the Internet. When I took the pic I just snapped it to show the groups. My software, Nikon Capture NX2, has a leveling tool that you can straighten lines that are not straight and had I posted just one photo I could have straightened that one easily but with two not lined up together I can see how you would think maybe the lens was at fault.

I'm sure whoever copied those targets for everyone to be able to use did so with a less than perfectly flat field type of lens. Nikon use to and maybe still does, make a flat field lens for copying purposes. A " tilt shift Lens" of a sort I think they use to call it. Great for architectural photography and would straighten in camera lines that bowed out and perhaps inward as well.

[Unclenick]

The shift lens is a different beast from a flat field lens. I have one for an old Olympus film camera. It is basically a normal wide angle lens mounted on a sliding platform, so the field of focus is curved. A flat field lens, as the name implies, is only corrected for photographing a flat object and has its field of focus flat.

Below is a Wikimedia Commons images of barrel distortion by WolfWings, and a barrel by Pearson Scott Foresman to show what the name comes from. (reproduced here in compliance with the Wikimedia Commons use rules). It's what I'm seeing; not very much of it but just a little. The yellow grid lines match uniformly at the bottom, as if that matched the center of the lens, and the middle vertical line tracks to the top. But the other vertical lines are not quite tracked to the top and the image curves slightly to fall inside them.





This is a pincushion distortion illustration by WolfWings:



Enjoy the use of On Target. It's become my go-to for determining group size and direction. A very useful tool.

[ColColt]

I once bought some "non-Nikon" lens many moons ago for my F2A and regretted it as it had bad barrel distortion...Sigma lens, I think it was, but; I don't recall the focal length. It was my first and last mistake. I stuck with Nikkor lens. The one exception was the tack sharp Vivitar Series I 90mm f/2.5 lens and a superb lens it was. I still have it but doesn't work well with modern digital cameras.

I am enjoying that program and having fun saving the information it gives. Marvelous little program.

While I'm still thinking of it it seems I had a flat field lens long ago for copying good old K64 slides. I can't recall what happened to it.