204 Ruger hot skinny barrels and accuracy

[Againstthegrains]

I'm curious about this one. I have a skinny barreled 204 Ruger (its thinner than a std Howa Barrel), neat little rifle. When I shoot  a group at 100m, the first 2 shots are always holes touching, and the 3rd is a "flyer" still within an inch, but off the group. If I cool the gun down, and start again, the same pattern. The third "flyer" is never in the same place. If I try to shoot more than 3 with a warm barrel, my groups go to paw paw. Is it possible that the skinny barrel heats up with the over bore caliber, that causes the accuracy goes to pot? or am I missing something?

[Tripodmvr]

1. Have you measured speeds for the 3 shots to see if that might not be the reason? Small cases are very sensitive to charge weight differences.
2. Do you use a suppressor when shooting? If so, the barrel channel needs a lot of free space as the barrel will bend and touch the stock.
3. The barrel steel could have a memory and the heat then causes a very slight bend. If the muzzle of a 24 inch barrel moves .0002m (.2 of a millimeter) the bullet is displaced by one MOA. (1 inch at 100yards)(29mm at 100m)

[Treeman]

I once wrote an article on this subject, I called it "the walking barrel".
I then one day found an article with a similar or same name.
There are two reasons that I know of for this happening.
The first is the skinny barrel heats up causing various results which causes various results in regards to POI. One of the happenings is action mounting tensions change, the barrel heats rapidly up which heats the stock up, in particular the barrel channel which then touch's where it did not or has more pressure where it was touching all along. Things change when things get hot - sounds simple, but it is such a understatement.

The second matter that can occur is far more likely in old steel than modern steel, but not impossible even in modern steels is an impurity, uneven metallurgy or even a bubble or bubbles in the barrels steel which will then cause all kinds of weird and wonderful things to happen when things heat up.
Remember as absurd as my writings are, these changes need only be .001 to have big effect down range at 100 m.
Thin is never good thing for repeated shooting, everything bad is exaggerated more and more the thinner you go.
Take a Lee Enfield that shoots well with its pencil barrel, shoot a mag of ten shots out, shoot a 3 group, move to next dot shoot a 3 group and repeat, no rapid fire, reload mag take time and shoot another 3 x 3 shot groups.
The first group or two you would buy that rifle any day, the last group or two, you would not buy a rifle that shoots like that.

My BSA Feather Light 1940 ish had walking barrel due to a flaw in the metal, it shot the same pattern every time.
Two shots touching, then started rising up and to the right, at shot 5 it started come back across to the left. It was so predictable that I could shoot groups on a page that were all first and second shot, then another group on page that were also all 3rd shot and another all 4 th shot. I could also reverse this by letting barrel cool down 5 mins and then hit group 3rd shot, cool down 15 mins and shot would hit group 2 and of course leave it 30 mins and hit back on first shot group.
 

[Treeman]

20 Years ago there was only 2 articles on the walking barrel, I see there are a few now. If anyone finds my article please let me know.

[Againstthegrains]

@ Treeman, that makes a lot of sense. The one thing is that it takes a lot of confidence in the shooter to say I know exactly where that bullet should have gone, and why did it not go there. I had to see the pattern a few times before it clicked, and wasn't just user error. I wonder if it is my bedding that covers the first 10mm of my chamber. Perhaps my chamber is heating up and pressing on the bedding? I'll grind a bit away and see?

[Treeman]

@ Treeman, that makes a lot of sense. The one thing is that it takes a lot of confidence in the shooter to say I know exactly where that bullet should have gone, and why did it not go there. I had to see the pattern a few times before it clicked, and wasn't just user error. I wonder if it is my bedding that covers the first 10mm of my chamber. Perhaps my chamber is heating up and pressing on the bedding? I'll grind a bit away and see?
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Try this first, take a washer and grind it to fit and place under action in the stock and then tighten up and go shoot. This will lift action thickness of washer. There are a few ways to do this using velomite gasket paper or aluminium tape etc etc, find best for you way to lift the action .25 of a mm, just enough to tell a story.
I once in desperation painted a stock white inside and then shot it till a story was transferred to the whit paint.

Thin barrels are kak - period 

[Ds J]

How tight or loose is the walking group? If it is still 1 MOA, or preferably smaller, why does it bother that much?

[Treeman]

How tight or loose is the walking group? If it is still 1 MOA, or preferably smaller, why does it bother that much?

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Well, the group may be anything, rifle to rifle. my BSA Featherweight was a tight inside a square 1 inch block within 4 - 5 shots. My Lee .303 shoots a half inch group first 3 shots, but becomes a hand size group within 12  shots in one session.

Only accurate rifles are worth having. 

[Ds J]

In that case, you would still be able to cull with a warm barrel. Does one need more for everyday application?

[Shotofrank]

I do not think that I would like to have a rifle that I know is going to shoot, "not where I aimed". To know that no-matter how well I shot, it would still shoot somewhere nearby my point of aim.

[Philip J]

Hey everyone

I think I am seeing the same thing in my 270. Incidentally it is also a Ruger American.
Shots 1 and 2 are touching and then 3 goes wild.

I have to test loads for it this weekend, (thanks again for the QL assist oom driepoot) and I am planning to let it cool between each and every shot, just to see if it makes a difference

[Treeman]

Hey everyone

I think I am seeing the same thing in my 270. Incidentally it is also a Ruger American.
Shots 1 and 2 are touching and then 3 goes wild.

I have to test loads for it this weekend, (thanks again for the QL assist oom driepoot) and I am planning to let it cool between each and every shot, just to see if it makes a difference

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3rd shot wandering off, usually a easy fix, usually heat related - usually the stock reacting to the change in temperature.