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Author Topic: tuning a rifle  (Read 348 times)

Offline pa deerslayer

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tuning a rifle
« on: January 01, 2014, 05:56:46 AM »
folks,accuracy? is merely a matter of controlling harmonics,this is done by adjusting components until a combination is found which does this job. the process of barrel whip.aka harmonics is circular,reducing this can also be accomplished with heavy stiffer barrels,and in some calibers shorter,but velocity is reduced,and components are a bit harder to adjust
     now here is the bottom line for me,accuracy is a must even for short ranges,under 300 yards,but a must for ranges beyond any weapons PBR
    there has here and every where always been talk about accuracy,caliber choice, a unlimited variety of cause and effect scenarios,and of course personal choice,most of which really means little when hunting whitetail,unless u advocate a 22 or a 375 magnum,meet a guy months ago at the gun shop buying 300 ultra mag rounds at 55 dollars a box for deer hunting,just giggled.
    EVERYONE HERE KNOWS I ADVOCATE THE 270 but i also know the same can be accomplished with 30 percent or more less powder in many other calibers,there is the personal choice scenario

Offline Dutch-Hunter

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Re: tuning a rifle
« Reply #1 on: January 02, 2014, 07:38:40 AM »
pa I hope you don't mind if I put my "spin" (Yes pun intended) on this.

When you said tuning a rifle your exactly right. However the is very little we can physically do to a rifle to tune it. We can float the barrel, bed the action and adjust the trigger pull weight. What we are doing to tune a rifle is actually tuning is the pill. To explain why lets look at a smooth bore shotgun barrel. Its wall thickness is very thin compared to a rifle barrel. As you know a smooth bore shotgun barrel applies no resistance to travel for (in this case) many little pills consequently doesn't whip. Sure if there is a Choke at the end this will cause some resistance in hopes to keep the pattern tighter. In a rifle the pill must be spun to stabilize it. Think about a baseball pitcher. If he throws the ball with no spin it is called a knuckle ball and it moves all over the place in its flight, he actually can only hope it goes where he aims. If on the other hand he applies backspin (fast ball) it slides through the air with more velocity and predictabelly rises. Lateral spin moves the ball crossways in its travel comonly known as a curve ball. By controlling the gyroscopic physics (spin) the pitcher has the advantage with enough practice.

If we loosly translate gyroscopic physics to bullets shot out of a rifled barrel it may be easier to understand. The first problem is inertia, the release. As the bullet moves down the barrel its mass weight combined with its speed it encounters the resistance if the rifling starts twisting the pill. The second law of physics, "every action has an equal and opposite reaction". So as the pill twists it also tries to twist the barrel. However the barrel is too stiff and can only flex against the force generated by the pill. Barrel whip as it is known. This is the phenomenon we as accurate shooters must figure out an predict. Lets use your beloved 270 as an example. The weight of pills available for it range from 100 to 160 grains. The 100 grain pill will not cause the same whip as the 160 grain one even at the same speed. What ultimately happens is the 100 grain will probably exit the muzzle at a different quadrant of barel whip as the 160 grain one. It is possible to get bot pills to impact accurately by repeatedly testing that pill in that barrel.

Then the human factor must be ruled out of the equation so testing is best off of a firm rest such as an sand bag or steady rest. Barrel whip is not as great with heavier barrels but it is still there. If anyone reading this does not believe how much a barrel moves they can prove it to themselve by trying the following experiment. Paying close attention to the point of aim. Shoot a series of 3-5 shots with the foregrip resting on a sand bag. Now shoot another 3-5 shots with the barrel resting on the sand bag. You won't believe the difference. What this test tells you is how much barrel harmonics there is. This is also why barrel floating is so important.

Shooting accurately with factory loads is simply a matter of finding out the point of impact from the point of aim for that batch of ammunition. Shooting accurately by reloading is a whole other ball game and has been well discussed and covered already in many topics.
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Offline Madgomer

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Re: tuning a rifle
« Reply #2 on: January 02, 2014, 10:23:39 AM »
Dutch & PA - as always, thanks for the excellent guidance.  I knew there was some deflection in the barrel on each shot, and that your accuracy is impacted by the things that impact the dynamics of the barrel, but never for a minute stopped to think that it is likely to be a twisting motion rather than bending of the barrel.  Your explanation makes sense.  When Browning came out with their BOSS system a few years back I got it in my head that bending was the more dominant factor - - the BOSS system won't do much to "tune" a twisting motion of the barrel will it?  Having been a shotgun & archery guy the majority of my life, this long range rifle stuff hasn't been too important for me, but as I'm now getting into coyotes & also thinking about going to shoot some prairie dogs some day, I've got a lot to learn in this space.
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Offline OLD FLORIDA GATOR

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Re: tuning a rifle
« Reply #3 on: January 02, 2014, 01:05:40 PM »
wow take notes, students the professor has spoken , well done as usual , prof. 


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Offline pa deerslayer

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Re: tuning a rifle
« Reply #4 on: January 02, 2014, 03:59:58 PM »
another issue dutch ,many shooters place one hand on the barrel,this also effects harmonics,as does barrel temperature,air temperature,pill seating depth,length,neck tension,blah,blah,blah,blah,and on and on.the mathematics involved are extreme,now that being said with the ballistic software on the market today just about any re loader  can become an accurate shooter and save lots of time testing.
        but they must always keep in mind that every weapon has its optimum component combinations that will produce accuracy.I have spent a lifetime as a hunter,shooter,ballistics expert,as with anything we do to do well u must PRACTICE,and spend the time.

 

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