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WHY is my first shot high?

Discussion in 'Handloading and Reloading' started by docsleepy, Apr 7, 2013.

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  1. BluegrassDan

    BluegrassDan Member

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    Looking forward to seeing your results with the new barrel.

    How many inch-pounds do you torque the action screws?
     
  2. docsleepy

    docsleepy Member

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    Good question. "Tight". Probably 75 inch lbs
     
  3. BluegrassDan

    BluegrassDan Member

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    Are you using an actual torque wrench with accurate settings? By "feel" just isn't accurate enough.

    I still stand by my thought that the action screws have uneven torque, and most probably the front action screw being looser than the rear. They should be alternately tightened in 5 lb increments up to around 60 inch pounds to ensure even tension into the bedding. No loctite for action screws, although I do use it on scope mounts.

    Looking at your last group of nine or so shots, notice how you've got one shot high, then it settled, then one low, settles again, a couple high around 1 o'clock, settles down, etc.

    It could be that your 6mm bench gun is less prone to inaccuracy due to action screw tension thanks to higher quality bedding.

    Just my hypothesis.
     
    Last edited: Apr 16, 2013
  4. docsleepy

    docsleepy Member

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    Interesting ideas.

    1. No, I don't use a torque wrench.
    2. Both screws were loctited. They are approximately the same torque.
    3. I'm the person who bedded both the 6PPC and the 7mm08. Similar technique.
    4. The 6PPC is an old Savage action where the threads on the front threaded hole are damaged. To make it work without having to re-drill and thread to a larger size (with fewer threads) I actually created a stud of the appropriate length, glue it into the damaged threads, and apply a nut from outside the stock. Savages aren't nearly as well regarded as $1000 specialty actions, but then again, I'm not made of money.

    In my experience, the alignment and smooth movement of the rifle within the front and rear rests is key to reducing vertical stringing. It is odd to me that virtuall ALL the cold-bore error is vertical. This rifle is a hunting rifle with a narrow forearm. I created a U shaped wooden shim with cutouts for the swivel screw heads, that allows the forearm to move smoothly within the front rest. This was part of what got the groups down to touching. Since the rifle moves within the front rest bags before the first shot is fired (I snug the sides up just until the movement is ever so slightly restricted), I don't think that anything really changes between the 1st shot and followup shots. I could be wrong there, but again, this is my attempt to recreate the exact situation that works with the 6PPC -- which has zero change between first and following shots.
     
  5. docsleepy

    docsleepy Member

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    By sliding properly in the rest, I mean so that the rifle tracks vertically and returns well. The 7mm08 in a cheap plastic stock, can't really do this perfectly. My 6PPC has a weighted stock made by a good (but not great) stockmaker. In the bags, the scope revealed that the aim moved diagonally rather than vertical when the rifle was slid. Indeed, the buttstock was not laterally symmetrical when carefully measured! A bit of duct tape carefully layered and added to make it symmetrical and voile'! The rifle aim point moves perfectly vertical.

    There is no way to get the cheap, light, hunting rifle to duplicate all this, but still, it is the FIRST shot that shows the repeatable, always upwards, error.

    Attached is a pretty good group while fireforming some Norma 6PPC brass for the reconstructed 6PPC, which got an Evolution trigger....since re-adjusted to 5 ounces. Also a Savage action, much better stock, Shilen stainless match barrel, installed by me, bedded by me, same bag / same rest. 100 yards. 5 shots. If the thing didn't weigh a ton and have such a light trigger and have NO WAY to put on a strap....it would make a nice deer-killing machine. When you're shooting clay pigeons with that gun, you pick which edge of the clay you plan to hit!
     

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  6. Andrew Leigh

    Andrew Leigh Member

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    Hi Docsleepy,

    your spread of velocities is much larger than I would consider acceptable. At that speed I would be real unhappy if the spread was greater than +- 15fps.

    Do you hand load?

    Read this article, it is a great piece of work.

    http://www.rifleman.org.uk/Fuller_group_diagnosis.htm

    Read from "Diagnosis" and concentrate around Fig 8 and the accompanying text.

    Cheers
     
  7. docsleepy

    docsleepy Member

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    Great points.
    I don't trust the chrono. Fails too often. Think I should have put up a diffuser

    Hand loaded.

    That article sure makes it sound like it is the stock or bedding. Some benchrest rifles are GLUED IN so bedding issue disappears.

    Maybe I should get a FAT wrench and loosen screws and try better.
     
    Last edited: Apr 17, 2013
  8. drcook

    drcook Member

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  9. docsleepy

    docsleepy Member

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    Well, I read that, but they still don't explain the physics of it. For example, one person said his cold bore shot was low. Mine is high. Why? Why one direction and not another?
     
  10. docsleepy

    docsleepy Member

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    Either my barrel is wicked, or there something wrong with my stock or bedding. This just doesn't happen with my six PPC, which is an expensive stock and an expensive barrel. But it also doesn't an happen with my Mosin-Nagant. And you can't call that expensive!
     
  11. Andrew Leigh

    Andrew Leigh Member

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    Hi Docsleepy,

    I am a great believer of process control. That is, the abilty to control a process and to willfully take said process out of control and then to be able to return the process back into control.

    Reloading is a process. So whats my point. Well simply that we firstly need to ascertain if your reloads are consistent or if your Chrony hates you. Having said which the chances of each first shot being the flyer would be highly unlikely but as stated the spread was rather extreme. But the ammo must be the first check.

    In my personal experiecnce faulty / lack of adequate bedding mostly presents as lateral groups and not vertical. Judging by the glob in the middle you can shoot, I am not one you believes in flyers (other than thoses induced by the shooter) you have a couple of "flyer" which probably were not you.

    A couple of things to have a quick look at (not trying to teach you to suck eggs here);

    -Is your barrel free of the stock? The old dollar note check.
    -In a previous post I recommended that you check the firing pin assembly, your symptoms are classic of a broken / weak firing pin giving intermittent strikes. Have you checked your shot cases for varing firing pin strike depth?
    - Do you clean your rifle after each range outing and then oil the barrel? If so do you make sure that all the oil is removed from the barrel before your first shot. An oily barrel can lead to 1st shot like yours.
    - Do you store your rifle with the firing pin in tension or relaxed? If relaxed it may be that the for the first firing, the spring has rejuvenated a bit and then after the first operation relaxes back to its slightly weakened state.
    -How many action screws to you have holding the barreled action in place?

    Cheers
    Andrew
     
  12. docsleepy

    docsleepy Member

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    1. Completely free floated
    2. I'll check that firing pin strike depth; hadn't thought of that
    3. I'm pretty sure it is stored cocked in the safe.
    4. While investigating this, I have tried everything, recently I have not been cleaning it at all.
    5. Two action screws, quite tight. Locktite it.
     
  13. docsleepy

    docsleepy Member

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    Maybe I should've bought a new stock, instead of the barrel. My six PPC is in a stock made by Rayhill.
     
  14. Hummer70

    Hummer70 Member

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    FWIW looking at the striker indent on a fired primer is not much help. It should however protrude .040"-.060" through the bolt face.

    The striker spring taking a "set" (get shorter from being compressed for years) is another possibility and unless you have the equipment to determine striker energy (I do) then you don't really know what you have. Properly made springs should never take a "set".

    In the testing business what we did with all compression springs was to remove them from new weapons and measure their free length and record it. Then every 1200 rounds the springs would be removed and measured again to see if they became shorter.

    Wolff Springs generally make three grades of springs, "factory replacement", then a heavier medium and an even heavier spring. I always upgrade to a medium spring at a minimum. The industry standard was relaxed a number of years back from having a Min .020" striker indent (on copper pellet) and only "recommending" .016" indent.

    Higher energy is recommended to assure ignition uniformity. Lets see if I can explain it. the industry pretty well figured out that .009" indent or less was a all no fire. Where .012" or deeper was a all fire. Frankford Arsenal found out in testing years ago that as the striker energy drops off vertical dispersion increased even though 100% ignition was being achieved.

    I have a M1911 Swiss rifle that gives .022" indent. I had a La Corona 98 Mauser that gave .024" indent and I can't get a US made rifle to give me over .020 with factory spring.One is near on 80 years old and the other is 50 years old.

    Another thing that has an effect is the amount of off center striker hits. Frankford studies also proved that up to a .020" offset there was no effect on ignition reliability but after .020" the misfire rate goes up. Which begs the question why are the gov't weapon specs allowing 1/2 diameter offset (of striker nose) to be fielded.

    Try the following:

    1. leave the copper in the bore but remove the propellant fouling quickly after firing.
    2. Use synthetic grease on patch and make multiple passes until the patches come out same color as they went it. I use Grease Auto and Artillery GAA or Grease Aircraft Wide Temp Range WTR which are NATO spec greases.
    3. The Swiss Army has used grease to clean bores over a hundred years now and I have never heard of a surplus Swiss rifle with a bad bore as received.

    I normally run about 20 greased patches in bore ten passes. This will remove about 99.5% of the carbon (which is the enemy here). You want a tight fit so when the patch goes in bore it presses snugly on the walls of the barrel. I generally use a .27cal black nylon brush of a smaller caliber and wrap a 30 cal patch on that to give me a snug fit. When finished I leave grease in the bore.

    A tight fitting patch will just leave a non visible trace of grease you cannot detect by visual examination. If you can see the grease left in bore your patch is not tight enough.


    I believe your first shot will not be nearly as far out of the group.

    Most importantly after your last shot remove quickly and get a greased patch downbore to remove the carbon. Carbon left to cool becomes hard and acts as an abrasive.
     
  15. Nevmavrick

    Nevmavrick Member

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    Another WAG. I appears to me hat the whole rifle is being "bedded" on the first shot. Comparing the hunter with the BR-gun is unfair to both. Also the M-N is different just by the fact it's different. I think it best to treat the gun as an individual.
    Barrels have a tendency to "squirm" in a more-or-less circle as they are shot, from pressure and heat. Most of the time this "squirming" is in a figure 8. With a light (the lighter, the more obvious) barrel, you try to nullify, more or less this tendency.
    Also, each powder, and charge, not to mention bullet, modify this tendency. That is why the first shot COULD be in any direction. By changing the load, the direction MAY be changed. My thought on THIS matter is that if you change powders, you'll find the direction the first shot goes will differ.
    I'm not real sure what the "guide" does in this matter, but I'd try it without. It may take a slightly different technique to BR the gun, but that's OK, too.
    I agree that it may be a natural thing to have happen, but it's too radical to allow on a hunting rifle. The difference HAS to be reduced!
    The light hunting barrel is quite often in need of upward pressure, which you've reduced by cutting some of the stock away (not a bad thing...yet) You might put more pressure UP by putting a business-card shim under the barrel at the tip of the forearm. Then, 2 or 3 more as the experiment continues. If it doesn't work, they can come out.
    MY opinion, FWIW, is change the powder first.
    Have fun,
    Gene
     
  16. docsleepy

    docsleepy Member

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    1. By using a pin with a piece of skotch tape as a transfer device, and trying different settings of the tape, I was able to get a measurement of the degree of primer pit This was not easy. I estimate AT LEAST .016 and likely .018"

    2. The firing pin pits are not exactly dead center. The fired primer is .143" wide, and the edge of the pit appears to be as much as .010" closer to one edge than another. However, that's pretty close to centered.

    3. The grease idea is fasincating, especially since my (possibly flawed) measurements indicate that the first shot might be considerably slowed.

    4. I don't have any "synthetic grease" but I'll give this a try. This is interesting. It seemed very much to me like something "left behind" was doing it. I have some gun grease and some disk brake grease. I'll look into this.

    THANKS FOR THE IDEAS!!!
     
  17. docsleepy

    docsleepy Member

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    Possible Solution

    OK, we may be making progress!

    I tried Hummer70's idea. The only "grease" I had readily available was some "gun grease" called "PRO-GOLD". So I got the biggest patches that I could get through the bore/bore guide and patched about 6 patches with some grease on them, each one at least twice. The gun had not been cleaned after the previous session. The patches started dirty and became progressively cleaner, to close to clean.

    Shooting was same as before, front rest, wood cradle for the skinny forearm, rear bag, firm hold, 100 yards, 16x scope. It was a busy day, so I only had about 15 minutes of sunlight left (range closes). Got three shots off. 1st and 2nd were amazingly close, and the third, while off a bit to the right, has almost the same elevation.

    Of course, one can only do ONE "cold bore" test at a time, so this is only 1 test. Will need to try this several more times, but at least the shots were similar.
     

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  18. Andrew Leigh

    Andrew Leigh Member

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    Great news.

    So if I understand this process correctly. The barrel is left with the copper fouling and only the carbon fouling is removed. Would this be an indication of a failing barrel which needs plating to perform as normal?

    @Hummer70. Surely this would not be considered normal practice on any barrel?
     
  19. docsleepy

    docsleepy Member

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    Good question. In the beginning, it was a factory fresh (cheap) $85 Savage sporter (thin) 7mm08 barrel, 22 inches long. It did get a special treatment a month ago which greatly improved its consistency and made the previously suspicioned cold shot problem become very obvious. (you can guess if you read the thread, "What you can do with a Mosin") I would guess that it has had around 500 shots, mostly in the middle range of power.
     
  20. 3212

    3212 Member

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    I have had this same problem with a 1958 Winchester model 70 in .243 caliber.So,I shoot 3 shots before the final sight in.Then I do not clean it before the hunt.I have taken more than 40 deer with it using this sight in method.No modifications to the rifle.After the hunt it gets a thorough cleaning.My longest kill shot was 270 yards.
     
  21. docsleepy

    docsleepy Member

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    3212: My problem was that even when left uncleaned, first shot would not be as predictable as others.
     
  22. 3212

    3212 Member

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    I understand the desire to have every shot placed precisely.It may be that my first shot at a deer is 2 inches from my point of aim.If I can see the deers chest it doesn't matter.I've usually got a 12 inch diameter target,maybe less if the deer is at an angle.I won't shoot at a tail.Now if you're in a shooting contest go for the precision.
     
  23. docsleepy

    docsleepy Member

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    Deer can be at great distances. Missed a 275 yard shot. 2 inch at 100 implies an angular error that makes 5" at 275 according to jbmbalistics. No one is a perfect shot. Add a small additional error and pretty soon you have missed or only wounded the deer.
     
  24. 3212

    3212 Member

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    On my 270 yard shot,I held high on the shoulder and the bullet entered the lower chest.So several inches higher would still hit the vitals.At that distance the bullet was beyond the midpoint of its trajectory.At the midpoint it may have been a problem.But I shot a buck at 180 yards facing me at 3/4 profile.All the others were from about 150 yards to 20 yards.The .243 has a pretty flat trajectory if you look at the charts.A cartridge with a different trajectory might cause problems. I never hold above the deer(off the brown).
     
  25. docsleepy

    docsleepy Member

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    Great advice! Certainly novice at hunting. Didn't even have a firearm until our current president. So lots to learn!
     
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