Importance of Standard Deviation

Don,

It sounds like you are talking about shorter range shooting. If I fire a 7 mm Sierra 175-grain SPBT at 2700 fps and again at 2650, at 100 yards the drop difference is only 0.1 inches. Nobody but a top-ranked benchrest shooter is even likely to be able to detect it on the paper, and maybe not even then. At 200, it grows to 0.4 inches difference, and at 300 yards it grows to 1 inch. Those numbers are all within what most people consider darn good shooting at those distances. But if you are shooting at 1000 yards, the drop difference grows to 16 inches and that's enough to cause you to miss a gong or popper or drop points on a target.

So, I think the answer to your observation about the increasing complexity is that when very few people were shooting at long ranges (before F-Class competition in particular), few people shot far enough for it to matter and most matches were held using targets developed for service rifles that didn't require super-precision. But between Bryan Litz and others spreading the ballistics gospel, it became apparent that people who had detailed technical knowledge won more matches or rose in the winning ranks more rapidly than those who didn't.

So, while it is still possible to win a match without deep ballistics understanding or to find good loads by more rudimentary trial and error, the people who delve into the science have been found to have a competitive edge. Competitors want that (or any other edge they can get; just look at what is spent on top equipment and supplies). The up-and-coming competitors don't want to cede that edge to the top competitors, either. So, with the help of computers and cell phone apps and some top people experimenting and publishing, the technical deep-dive has taken on a life of its own.
 
Standard deviation is the result of mathematical massaging of the data and gets a lot of attention on the gun boards because most consumer chronographs will spit it out automatically. In my use it is just a general indication of ammo quality because I am not doing statistical analysis of my ballistics.

Extreme spread is actual data and is what the OP needs to be watching.
At long range velocity variation equals elevation variation, accentuated by the low velocity of a cast bullet driven by black powder. Also, the BPCR shooter has less scope to look for nodes and no option of hanging weights on his barrel.

I don't know where the OP will end up with .38-35 Nitro.

The best small bore I heard about was Dan Theodore's development of the .35-55 Maynard, but he was still shooting with black powder and complaining that the NRA disallowed it because they weren't sure it was a standard 19th century chamber.
I saw a junior shooter shooting a round with .357 Maximum brass and a long heavy bullet seated very shallowly to make room for powder. I don't recall what period round that was supposed to approximate.
 
and tuning to muzzle swing makes velocity variation have less effect
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How can “muzzle swing” impact external ballistics? Velocity and BC Sd are all about minimizing the variation in flight. I’m wondering as I know that you know your stuff.


, I'm not a match shooter but have several hunting rifle's that will hold close to 1/2" group's and I haven't a clue nor do I care what the SD is!
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...and that works great at 100-400 yards, but things will start open up without understanding variation beyond that.
 
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Everything is relative. There are some 1000 yard guys who have turned in 5 shot groups under 1.5". To do that SD is more important than the level of accuracy you're going to achieve with a 45-70 or 38-35.
 
And for a meaningful SD statistically, a minimum sample is 10 is required. More is always better of course. I shoot 15. Allows me to throw out obvious fliers if applicable. My testing is mostly with pistol/revolver cartridges as that is what I like to shoot. I've also found that SD is usually always in the ballpark of 1/3 the Extreme Spread. Therefore I care more about the ES. Consistency never hurts accuracy, it can only help of course. Yet, the load still may not be accurate for some reason. That's why we work up loads to find 'the' load we feel is 'right'. My two cents.
 
Nathan said:
How can “muzzle swing” impact external ballistics?
Click to expand...

Most rifles have their barrel bore line axis above the point of stock contact on the shooter's shoulder. This causes a portion of the recoil to go into attempting to rotatate the rifle up and around the point of contact (it's what you see as muzzle rise). This cracks the whip on the barrel, resulting in the muzzle vibrating up and down, sinusoidally as shown in Mode 3 in the table of animations on this page. Like any sinusoidal motion, the rate of change in the muzzle's angle is greatest as it passes through zero deflection or value between the extremes of the swing range, and slowest near the extremes of the swing. If you time the bullet to get out near a valley or a peak, you can pick a slope in the rate of change that tends to compensate for small velocity variations.

The mechanism for that compensation in the valley is that if a slower bullet clears the muzzle when it is on the upswing, the velocity of the momentum the bullet picks up in that upswing will go the bullet as an upward vertical addition to its initial vertical velocity component that gravity and drag must overcome before the bullet reaches apogee and starts to fall. This is in addition to having a higher angle of departure. These will make the bullet impact higher than it would if it cleared the muzzle at an unmoving position at the bottom corner of the swing with no vertical motion (the static phase of the oscillation). So, if you can get the average bullet out at the right moment in the swing, such that faster bullets carry less upswing velocity and slow bullets carry more, they can all land at the same poi at some range at which the trajectories cross over one another and for a good distance before and after the crossover point if the lines don't diverge too fast. All the above is why barrel tuners shrink groups, regardless of exact load specifics.
 
Unclenick, I don't understand how the muzzle axis angular rate of change upward being at right angles to the LOF increases bullet velocity.

With tuners set correct, the LOF angular rate of change is faster for the higher bullet velocities, slower for lowest velocities.
 
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Centrifugal force literally "flings" the bullet outward -- some small amount of added velocity.

(by my calculation:
- Average of 0.033 pounds of "fling" force
- on a 150gr bullet
- in a 2-ft barrel
- muzzle rotating upward at 10ft/sec recoil during bullet transit)
 
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Bart,

Yest there are actually three ways of looking at the working of the tuner. The one you are describing for a muzzle approaching the top or crest of the swing, the reverse which I described and that applies at the bottom or valley of the swing, and then there is simply the muzzle position pause during the overall elevating motion of the barrel that is brought about by downswing. I failed to segregate all that out. But even Varmint Al mentions debating about exactly where the tuning occurrs. The only person who measured the missing information element was Harold Vaughn, who put inertial sensors on the muzzle of a rifle, but was using them to detect moments of inertia rather than the tuning event. But it could be resolved by puting an inertial sensor and a strain gauge at the muzze to detect bullet base arrival at the end of the barrel so we can see how the phases of the swing and bullet exit overlap.
 
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