Vo vs. Powder Charge & Type

Discussions of powders, bullets and loading information.

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beltfed
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Re: Vo vs. Powder Charge & Type

Post by beltfed »

Yes, Bruce,
And then, especially in F Open, it starts over again when the rifle gets to 1000 rds or so and
you have to work up loads for the new barrel and in the process use up maybe 10-15% of the life doing so. $$$$$$$$$$$$
I have picked up 4- 6.5x284 barrels from my National Champ F-Class Open friend that would no longer shoot into 1/3 min
and so were no longer useful for him. One Obermeyer barrel, I had set back and rechambered to 260 rem on my Savage 110 left hand single shot action to "play with"
beltfed/arnie
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Raven
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Re: Vo vs. Powder Charge & Type

Post by Raven »

bruce m wrote: Tue Sep 01, 2020 12:11 am the fclass technique is all about harmonics.
mostly it is used when changing lot nos of powder if the burn rat varies a little, or as the throat wears, allowing velocity to drop off.
it is amazing how groups tighten up again when coming back to the accurate velocity.
a lot of work goes on shooting various types of ladders and chronographing to get a good harmonic node at low std deviations.
bruce.
You guys are the only ones I see talk about Velocity as it pertains to Accuracy.
Now do you see the harmonics of the barrel change with a change in powder, (say 1.5f to 2f)?
bruce m
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Re: Vo vs. Powder Charge & Type

Post by bruce m »

raven,
you ask the question i also ask.
bruce.
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BFD
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Re: Vo vs. Powder Charge & Type

Post by BFD »

Raven wrote: Tue Sep 01, 2020 12:16 pm
bruce m wrote: Tue Sep 01, 2020 12:11 am the fclass technique is all about harmonics.
mostly it is used when changing lot nos of powder if the burn rat varies a little, or as the throat wears, allowing velocity to drop off.
it is amazing how groups tighten up again when coming back to the accurate velocity.
a lot of work goes on shooting various types of ladders and chronographing to get a good harmonic node at low std deviations.
bruce.
You guys are the only ones I see talk about Velocity as it pertains to Accuracy.
Now do you see the harmonics of the barrel change with a change in powder, (say 1.5f to 2f)?
Why would it change? The barrel's "harmonics" are what they are. They don't change unless you change the barrel.

If you hit a tuning fork with a 2# hammer and again with a tack hammer, it emits the same sound.
bruce m
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Re: Vo vs. Powder Charge & Type

Post by bruce m »

brent,
if you shoot 3 shot groups of differing powder charges, the same powder,targets show centre of groups forming a sine wave on the target.
with lighter weight barrels, the sine wave is more pronounced.
the further away the target, the more obvious the sine wave is.
imagine a horizontal line with the half the sine wave above, and 1/2 below.
as you shoot your charges, the bullets might start climbing, reach a peak and then start descending until they start rising again.
sometimes you can just see this at 100 yards but not always.
at 500 or 600 yards the horizontal line might become slanted.
at the bottoms or tops of the sine wave there is little difference in elevation of the groups, and these points are called nodes.
at the top, a good load is just past the node, and at the bottom, a good load is just before the node.
this is because the slower bullets are actually shooting a little higher than the faster ones, and the further out you get the more they will come together, rather than spread apart if the fast ones are higher and the slow ones are low.
all being the same, powder type, seating depth, bullet consistency etc, these nodes relate to velocity.
lose velocity due to throat wear of a new lot of the same powder, and you go off node.
this is demonstrated by increased vertical, and usually happens during a big comp and when you are in front.
maintaining a consistent relation of ogive to throat is also important.
if adjusting velocity will not fix it, you have a cooked barrel, or ceramic carbon fouling might be some of the problems.
really heavy barrels might not actually produce a sine wave so much, but more of a climbing of group, followed by a flattening out on the node, then climbing again.
bruce.
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BFD
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Re: Vo vs. Powder Charge & Type

Post by BFD »

Bruce, I'm going to disagree (surprise!). First, no one can demonstrate a sin wave with three points. Period.

But beyond that I think your idea of how barrels vibrate is far too simplistic and 2 dimensional. This has been discussed by others in some detail.

In any event, the real point is that in all cases the barrel vibrates the same, regardless of your powder. That does not mean that your bullets should arrive at the same point. Barrel harmonics are a very small part (at most) of bullet accuracy (I suppose we really should say precision, in this instance).
bruce m
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Re: Vo vs. Powder Charge & Type

Post by bruce m »

brent,
disagreement is what makes the world go round and is healthy.
in my defence i will say that the sine wave here is not demonstrated by 3 points.
you might shoot 10 groups of 3 shots, each point being the centre of each group.
these 10 or so groups might not complete a full cycle, but if you get the bottom or top of the curve ate sane pressures or useable velocity, you can get a good node.
this method of getting best accuracy from a barrel is pretty much a common thing nowadays.
when you get as good as you can, then trying different primers and seating depths can tweak a little more.
but the that might affect velocity, so you adjust that again.
you are right about being 2 dimensional.
the problem is that adding the 3rd dimension relies on absolute wind reading at the ideal ranges to do these tests.
i cannot say whether bringing another powder to the same velocity will achieve the same level of accuracy, as i have never tried it.
after all this, guys with tuners then start turning the tuner in the hope if improving even further.
there are programmes available that purport to give a best barrel length for most accuracy, but that is above my pay grade.
i do know that loads worked up as described will give way less vert than loads in between nodes.
narrow nodes can be a problem as the day warms up, the load going off node in the warmer afternoon.
benchrest shooters learn how to adjust powder charges as the day goes on, as they load on the range,
there are now fclass guys that turn their tuner a little as the day warms up.
myself, i just keep trying to improve my wind reading.
bruce.
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BFD
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Re: Vo vs. Powder Charge & Type

Post by BFD »

Bruce, you are talking about the effects of different loads, different velocities etc, but NOT difference in harmonics. There is no difference. Get out of small arms ballistics for a while and look at harmonics of tubes. Any tubes. They are all qualitatively the same.
BFD
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Re: Vo vs. Powder Charge & Type

Post by BFD »

The guys playing with tuners on their barrels ARE changing harmonics because they are changing the tube. The rest is not about altering harmonics.
bruce m
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Re: Vo vs. Powder Charge & Type

Post by bruce m »

brent,
you are right about the harmonics, but i suspect we are actually on the same page.
it is because harmonics remain the same that altering the velocity allows us to tune a load.
by altering the velocity, we alter the point in the harmonic where the bullet leaves the barrel.
at the top or the bottom of the harmonic is where the best accuracy is.
this is because loads with different velocities are in a flatter line on the target, offering more forgiveness to velocity spread.
excuse my lack of scientific terminology, but hopefully i have illustrated the point i am trying to make.
you are also right about tuners.
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beltfed
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Re: Vo vs. Powder Charge & Type

Post by beltfed »

Bruce,
Finally. You said it:
Altering the point in harmonic "whip" of the barrel where the bullet leaves the barrel.....
beltfed/arnie
bruce m
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Re: Vo vs. Powder Charge & Type

Post by bruce m »

arnie,
because i just got to word it better.
a nice lad but a bit simple.
bruce.
ventum est amicus meus
semtav
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Re: Vo vs. Powder Charge & Type

Post by semtav »

bruce m wrote: Tue Sep 01, 2020 9:15 pm brent,
you are right about the harmonics, but i suspect we are actually on the same page.
it is because harmonics remain the same that altering the velocity allows us to tune a load.
by altering the velocity, we alter the point in the harmonic where the bullet leaves the barrel.
at the top or the bottom of the harmonic is where the best accuracy is.
this is because loads with different velocities are in a flatter line on the target, offering more forgiveness to velocity spread

To a flat earther then, velocity would be all that mattered. Find the perfect velocity that it leaves the barrel and ypu have it licked.

But in a round world im thinking its more about lapsed time from ignition until the bullet exits the barrel.
martinibelgian
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Re: Vo vs. Powder Charge & Type

Post by martinibelgian »

Nope - velocity alone won't do it - barrel time is also important as it determines the point where the bullet leaves the barrel. It's not because the MV is identical that barrel time is also. Not to mention ES...
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desert deuce
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Re: Vo vs. Powder Charge & Type

Post by desert deuce »

Sorry, can't join the discussion, I am not a member of the Flat Earth Society or the Bipolar Elite.
Sometimes you get the chicken, and sometimes you get the feathers!
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