Cold-bore variation . . . ?

Discussion in 'The Basics, Starting Out' started by Country Bumpkin, Dec 18, 2017.

  1. Country Bumpkin

    Country Bumpkin Well-Known Member

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    Hello All, I'm not sure what's going on here and was hoping you could help. I traded my custom rifle and am waiting on a new one to be built . . . so in the meantime I bought a project gun just to see what happens.

    Attached groups are at 300 yds with my Ruger American Predator in 6.5 CM at 300 yards, not very much wind (maybe 3-5, I’m not practiced at estimating wind yet). Cold bore shot is always to the right of shots 2-4. I just noticed while posting this that my sighting group (low and to the right) did the exact same thing and I didn’t capture in my group measurement. Look to the right, off the cardboard and just nicking the plywood.

    Anybody else having horizontal cold bore displacements? I would have assumed that cold bore would typically vary vertically more than horizontally. You will see I measured one group twice (if I could eliminate the cold bore variation I’d have a 1/2 min Rifle).

    Explanations, Resolution, comments, flaming....? Thanks everyone.
     

    Attached Files:

  2. Country Bumpkin

    Country Bumpkin Well-Known Member

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    Oh, and you will notice that I posted one group twice. I measured that one without the first shot of the group and it's just under 1/2 minute . . . If I could get my first round shots to center up with shots 2-4 . . . I'd be onto something neat . . . for $400.
     
  3. Country Bumpkin

    Country Bumpkin Well-Known Member

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    Really . . . nobody has any input? Nobody wants to take the opportunity to poke fun at the ignorant??
     
  4. JSHKS

    JSHKS Active Member

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    I have an old custom wood stock rifle from the early 60's.
    First shot is where I want it. The next two or however many all group to the right, good group to boot. Wait at least 20 minutes after ONE shot and it will stack or cut the first hole.

    I am hoping a rebedding job will fix it.
     
  5. dfanonymous

    dfanonymous Well-Known Member

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    old bore deviation is a thing. Back in the day (snipers) we'd use a data book and note the offset for cold bore and add it into the solution or hold on it. Now days there are apps with that will say cold bore, or zero offset that you can plug that deviation into and it will correct it into the solution.
    Reasoning is like usual, the steel tolerance heating up, flexing the action and the stock, fouling in the barrel, and causing a slight harmonic deviation. The only issue with that is when it isn't consistent. If its consistent than you can compensate for it.
     
  6. dok7mm

    dok7mm Well-Known Member

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    A couple of things: 1. Make sure your scope and rings are tight and you don't have any cant in your hold from shot to shot. 2. If you are shooting factory ammo (you didn't say), it may be a seating depth your rifle doesn't like.
    3. If your scope had a parallax adjustment, make sure it is set where cross hairs don't move with slight head movement. 4. Are you confident that your cheek weld and hold are completely consistent from shot to shot? 5. Have you checked your stock clearance on cold bore vs warm bore?

    Check out the simple things first, before you panic. At three hundred yards, even the little things make a larger impact on paper. Do some dry firing exercises to reduce shooter error. Good Luck!
     
    jrock likes this.
  7. Country Bumpkin

    Country Bumpkin Well-Known Member

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    Thanks guys, this is exactly what I was looking for. I'll start checking these off the list next range day and will report back on what I learn.
     
  8. Snyper708

    Snyper708 Well-Known Member

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    Also check the torque on your action screws.
     
  9. Shane Lindsey

    Shane Lindsey Well-Known Member

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    You can try to shoot the cold clean bore shot and then the group and then put it away for the day. Next time out, take the same four shots and see where they are. Maybe even do it again another day for some consistency. I have listened to guys talk about not cleaning for a few hundred rounds, that is fine if you shoot often, but if you don’t and live in any humidity you may look at puttting it away slightly wet. I tried to put one away dirty thinking my cold bore would be on and it sat for about six months. No bueno!

    Mapping the cold clean bore can be done similar to what I listed above but instead of shooting it dirty go home and clean it back to bare steel and see where it shoots. Then repeat. Every time I did this the cold clean shot was always out but not predictable enough to map. Now unless the rifle shoots cold clean bore into the group it don’t go out unless it’s fouled before hunting season. FWIW all my custom barrels shoot to the same group cold clean. Factory are a little more like you describe.

    Another thing I try to do is dry fire a few just to warm up my shooting mechanics.

    Good luck and report back whatever method you use.
     
  10. jrock

    jrock Well-Known Member

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    I map all my guns. I start from clean and map the first 4 shots shooting somewhat quickly as if I were shooting at game. I then leave it dirty and try the cold bore mapping with it fouled. I found my guns were fairly predictable with a clean bore first shot. However, I found that having two fouling rounds down first in a cold bore gave the same POI as the next 4. So I make sure to have two rounds down the barrel to foul it before hunting season. I have only tested off the shelf rifles at this time.
     
    dfanonymous likes this.