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Thread: Testing loads at 50m instead of 100m

  1. #16
    Member Sasquatch's Avatar
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    Quote Originally Posted by gundoc View Post
    Not so. Whilst they are spinning as fast as they are going to does not mean they have settled into their 'sweet spot' and are fully stable. The distance that starts is a variable that changes with various projectiles and starting velocities. The Mk VII .303 is a classic example with the maximum stabilsation range being from 200 to 900 yards. Ballistics is far from an exact science and is full of variables.
    Bang on. To reinforce what @gundoc was meaning, check this video: Although on a much larger scale and not an exact comparison, the projectile that leaves the 'tank' is in no way stabilized.

    Skip to 6:10


  2. #17
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    I'm a strong believer of groups not tightening up at longer range. In practice you might see it but over a large average it's not possible. Unless someone can show me actual scientific reasoning how a bullets pass can change mid air consistently without external forces....

    To answer ops question I reckon 50m isn't a good idea as you will possibly be shooting just a ragged hole.
    Micky Duck, dannyb and caberslash like this.

  3. #18
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    agree,if its 2" at hundred it wont be smaller than 2" any further out....it might stop wobbling around but it wont tighten up. it COULD feasably stop wobbling or cirling around its axis a little so MIGHTNT double group size at double the range,but it sure as God made little green apples CAN NOT suddenly shrink groups by now deciding to change path to where you desire it to be Vs where it was.
    75/15/10 black powder matters

  4. #19
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    If anything I prefer to shoot groups at 200 so I can see any oddities starting to rear their ugly heads
    unless they are subs then its 30-40m

  5. #20
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    Greetings All,
    An interesting discussion. I do most of my chronographing and initial load development at 60 metres as this is convenient here. Final zero and testing is done at 108, 172 or 198 metres depending on the rifle and its capabilities. The odd ranges are due to the availability of a bench and backstop at these ranges. We all have an idea of the range that we are competent to shoot at and my belief is that we should validate our trajectory by test firing out to at least 2/3 of that range. The mesage here is that do not zero at 50 metres and pretend you know where your projectile is going at 300 let alone 500 metres. As for groups tightening at 200 metres from 100 metres when measured in moa or mrads I have seen this too often for it to just be chance. One of the factors here may be parallax or the apparent shift of the reticle due to head position. Non adjustable scpoes will have some parallax shift at 100 metres and more at 50 metres.
    Regards Grandpamac.

  6. #21
    Member Micky Duck's Avatar
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    so were these mysterious shrinking groups still centred around the bull or off to one side or higher or lower????
    one other factor that comes into play is you are aiming smaller at 200-300 yards and concentrating more as any little shake takes you off centre by twice or three times as much.
    Bill999 likes this.
    75/15/10 black powder matters

  7. #22
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    Quote Originally Posted by grandpamac View Post
    Greetings All,
    An interesting discussion. I do most of my chronographing and initial load development at 60 metres as this is convenient here. Final zero and testing is done at 108, 172 or 198 metres depending on the rifle and its capabilities. The odd ranges are due to the availability of a bench and backstop at these ranges. We all have an idea of the range that we are competent to shoot at and my belief is that we should validate our trajectory by test firing out to at least 2/3 of that range. The mesage here is that do not zero at 50 metres and pretend you know where your projectile is going at 300 let alone 500 metres. As for groups tightening at 200 metres from 100 metres when measured in moa or mrads I have seen this too often for it to just be chance. One of the factors here may be parallax or the apparent shift of the reticle due to head position. Non adjustable scpoes will have some parallax shift at 100 metres and more at 50 metres.
    Regards Grandpamac.
    I agree you can shoot tighter groups at distance due to things that have no correlation to ballistics, e.g scope parallax, shooting style, eye sight, target size. Not a bullet suddenly correcting alignment and creating a smaller group
    Micky Duck likes this.

  8. #23
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    Quote Originally Posted by gundoc View Post
    Not so. Whilst they are spinning as fast as they are going to does not mean they have settled into their 'sweet spot' and are fully stable. The distance that starts is a variable that changes with various projectiles and starting velocities. The Mk VII .303 is a classic example with the maximum stabilsation range being from 200 to 900 yards. Ballistics is far from an exact science and is full of variables.
    Also boattails take a distance to stabilise which is why they are suited to longer range shooting and why benchrest shooters use flatbase at closer ranges. Yes?
    I know a lot but it seems less every day...

  9. #24
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    Quote Originally Posted by Jhon View Post
    Also boattails take a distance to stabilise which is why they are suited to longer range shooting and why benchrest shooters use flatbase at closer ranges. Yes?
    nope....boat tails are more slippery through the air so hold up better in the wind etc,they are more aerodynamic...flat base are cheaper to make and grip loose n worn bores better and there was a theory they expanded better and held together better in arse end at one point in time...... use what you have on hand,the ONLY advantage to boat tails for the likes of me who doesnt shoot past 300 often,is they are oh so much easier to load into case....I can still miss just as well with them.
    Marty Henry and caberslash like this.
    75/15/10 black powder matters

  10. #25
    Member Marty Henry's Avatar
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    Theoretically there is a period of maximum stability for a projectile which depends on its length, rate of rotation and velocity more than anything else.
    Think of a spinning top it starts off with a slight wobble then stableises, as it slows at some point it begins to slowly wobble a bit following an arc around the point. As it slows further the wobble gets bigger till it finally falls over same thing with bullets

  11. #26
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    Quote Originally Posted by Marty Henry View Post
    Theoretically there is a period of maximum stability for a projectile which depends on its length, rate of rotation and velocity more than anything else.
    Think of a spinning top it starts off with a slight wobble then stableises, as it slows at some point it begins to slowly wobble a bit following an arc around the point. As it slows further the wobble gets bigger till it finally falls over same thing with bullets
    But if you started a spinning top in the middle of a circle, and it wobbled to the left, it wouldn't then automatically come back to the centre each time
    Bill999 likes this.

  12. #27
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    Hi everyone. Sorry for being late returning to the party, but was away for the evening. Just to clarify... I was meaning testing loads at 50m, not sighting in. I do sight in at 100m, but with load testing I was wondering how much variability the actual shooter has at 100m compared to 50m.

    I'm sure that many on here are much better shots than me and can shoot more consistently than me. But I was thinking that it only takes a slight variation of the shooter's ability to override the difference in the powder weight when working up a load. For example; I can shoot my 223 more accurately than my 308, as I suppose most can. And my 303's are harder to shoot accurately because the cheek weld isn't as good. All of which is far more noticeable at 100m,

    What I was thinking of trying was to work up the loads at 50m and then check the best at 100m to suss a load for good hunting accuracy. My set up isn't a bench rest style of situation, it's lying n the paddock and walking back and forth to check each group. Which again, probably affects accuracy (shooter capabilities).

    When sighting in I use the info from the Nikon Spot On programme to use at 100m. I've found it really good. Cheers for all the input.
    dannyb likes this.

  13. #28
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    Quote Originally Posted by Micky Duck View Post
    nope....boat tails are more slippery through the air so hold up better in the wind etc,they are more aerodynamic...flat base are cheaper to make and grip loose n worn bores better and there was a theory they expanded better and held together better in arse end at one point in time...... use what you have on hand,the ONLY advantage to boat tails for the likes of me who doesnt shoot past 300 often,is they are oh so much easier to load into case....I can still miss just as well with them.
    Guess i shouldn't read articles like this one then...

    "In the images taken during the Guns & Ammo TV test, the boattail projectile is entirely overtaken and surrounded by the propellant gases. This is not the case with the flat base. It is never completely overtaken by the propellant gases. The flat base on the right still has its nose protruding from the propellant gases and the shapes of the blast clouds are completely different. This suggests that the boattail bullet allows more high velocity gases to flow around it in the reverse flow stage than the flat-base projectile.

    An additional test was done with the barrel approximately 5 inches out of the field of view of the Schlieren system in order to look at when the two projectiles cleared the influence of the muzzleblast. These images show the flat base clearing the muzzleblast quite a bit sooner than the boattail. In fact, the video shows it takes five frames longer for the boattail projectile to clear the muzzleblast. The flat-base projectile will clearly be influenced less by the muzzleblast than the boattail projectile."

    and

    "The Schlieren images show that some propellant gases blow past the boattail projectile before it seals the bore. This can have adverse effects on the projectile. The gases that travel past the projectile are very hot and travelling very fast.

    Despite how brief this propellant gas blowby is, it can result in non-*uniform deformation of the projectile, or flame cutting, of the jacket. This can result in erratic flight of the projectile and is the cause of the troubling fliers we have all seen in our shooting groups from time to time. I’m not saying these things always happen, but it does create the potential for them to happen.

    Perhaps the most important takeaway from this test is the response of the boattail projectile versus the flat-base at the muzzle’s exit. The larger and longer-*lasting reverse flow on the boattail projectile can have a significant effect on its performance. With the sloping boattail, the reverse flow can produce a lift force on the boattail causing yaw and essentially making the projectile wobble. The duration of this lift force is very short, but it can have a significant effect on the projectile’s flight performance. This can cause larger groups and contribute significantly to the time it takes a projectile to go to sleep. Again, I’m not saying this will always occur, but the potential is definitely there. This dynamic condition does not exist with the flat-*base projectile."

    and

    "As you can see from the images and the analysis, the boattail projectile has much greater potential for undesirable things to happen. The boattail projectile has a greater sensitivity to factors not being perfect, either in the barrel or at the muzzle. The boattail projectile would be more sensitive to a large throat, throat wear, a damaged crown or worn rifling at the muzzle. If you have a rifle that won’t shoot very good groups with a boattail projectile, try a flat-base bullet and see if it results in better groups."

    https://www.gunsandammo.com/editoria...ectiles/375628

    The real world application of this particularly applies to old battle rifles like the 303B. Most of the reading I've done suggests flatbase projectiles are highly preferred over boattails for the 303B - where "large throat, throat wear, a damaged crown or worn rifling at the muzzle" issues would be pretty common. So may not apply quite so much to the highly tuned close spec target or hunting rifle of today, but still, its difficult to get past the fact of potential gas produced yaw/wobble for a boattail at the muzzle of any rifle as this is a issue specific to the projectile configuration rather than the rifle. Being a legend in my own google-time, this would be why I recollect other references to boattails needing some distance to "settle-down" in flight. But maybe its not so much them settling down as them not being upset further as much as flat bases by other factors such as side-winds.
    I know a lot but it seems less every day...

 

 

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