Is Faster or slower generally best?

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bruce m
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Re: Is Faster or slower generally best?

Post by bruce m »

mike,
you seem to be keen to condemn what is known and able to be calculated methematically without trying to understand it first.
bringing patch stripping into this discussion is absolutely futile and pointless.
it appears to be a way of avoiding the point of the discussion by taking it somewhere else.
the fact that if you have a zero of some kind on a rifle, you can calculate sight adjustments for any other range accurately with all factors taken into account proves the point.
it is so calculateable that long distance disciplines have had to ban the use of labradar chronographs in competition.
this is because if a shot goes high or low, and velocity reflects this, that shooter has a calculateable advantage.
the same with deflection if you can feed ALL the factors into the equation.
and spindrift as well.
if you are going to understand this you need to do the work necessary to do so without avoiding the issues.
before you can play jazz, you first of all have to learn to play the instrument.
bruce.
ventum est amicus meus
mdeland
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Joined: Mon Nov 20, 2006 1:47 pm

Re: Is Faster or slower generally best?

Post by mdeland »

I was using the patch expulsion as an example of something thought true that wasn't,not use it to change the subject. I'm asking the questions that keep the thread going on speed and deflection with some counter thought ideas I have had and others I've read about.
Your obviously convinced that drag is the only factor influencing deflection and I suspect there is more involved and am curious to find out what other forces are at play.
bruce m
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Re: Is Faster or slower generally best?

Post by bruce m »

you need to dig deeper on the basics to make such questions meaningful.
come back to accurate calculations can be made for wind deflection, both horizontal and vertical, and sight adjustments for range knowing b.c. and velocity, and try to work this out first.
bruce.
ventum est amicus meus
mdeland
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Re: Is Faster or slower generally best?

Post by mdeland »

Got it all figured out then huh ? There's only one sure thing to know about knowledge on any subject and that is, it is never complete.
bruce m
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Re: Is Faster or slower generally best?

Post by bruce m »

no i don't have it all figured out but am working on it.
you are right no knowledge is ever complete.
however you should not start condemning something until you at least understand the claim.
in this case that claim, at least in basics, can be proven mathematically.
heck you can even buy devices and programmes, and there are free programmes, that do the calculations for you, and you can test the answers by shooting.
when you grasp the basics, maybe debating the finer points could be relevent.
an example of this might be twist rates required for stability in transonic flight, and nose shapes affecting stability.
however if you want to go to places like that you need to throw a lot of money at it in barrels and bullet moulds, and spend a lot of time doing it.
bruce.
ventum est amicus meus
mdeland
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Re: Is Faster or slower generally best?

Post by mdeland »

I believe I have a fairly good grasp on the basics of deflection and drop regarding jacket bullets but as we have very little, if any published data on BPCR bullet deflection and drop figures, we are forced to do a lot of extrapolation and guess work from what is known of 22RF data and jacket bullet exterior ballistics.
We don't even know for sure the real BC that our lead bullets start out with so the notion all we have to do is consult a chart and dial in the deflection figures is not reality. What you infer are established known facts are not, in relation to the bullets we shoot, they are at best WAGS (wild ass guesses) so we shoot, observe and crank until we get it right for a shot or two then the conditions change.
I don't believe drag alone dictates deflection from what I learned from the Sierra manual, especially the flight of lead bullets that change when fired from what they are before hand.
Regarding jacket bullets ,Sierra says time of flight is the major influence dictating deflection. They discuss a number of forces involve in deflection not just drag. These are professional ballistics experts writing these manuals and charts and they're saying there is much more involve than drag alone causing deflection. '
No one I have ever read is shooting any .22 RF bullets from 600 to 1000 yards and mapping their deflection and drop. This means how they behave out to a max of 200 yards tells us very little about our bullets at extended ranges. And so we extrapolate, guess , crank in a value, observe and adapt.
bruce m
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Re: Is Faster or slower generally best?

Post by bruce m »

you can easily work out the b.c. of our bullets, by measuring the velocity at the muzzle and comparing a number of drops at different ranges.
you have to use the correct drag model, e.g. g1, g7 etc.
it is easy to work that out.
so now you have a b.c. and a velocity, and all you have to do is the total trajectory calculation.
22 rimfire, cast centrefire, jacketed centrefire makes no difference.
once you have the b.c. and the muzzle velocity, you can calculate deflection accurately.
the problem is applying it, as you have to include all factors in the equation, and that takes a lot of experience shooting in the wind.
william metford mage wind charts in the 1860s that were accurate for sideways deflection and for elevation changes also caused by the wind.
shiloh used to and possibly still does sell one of these.
in my own shooting i made wind charts from ballistic software, and never missed the target on a first sighter out to 1000 yds, often scoring quite well.
drag is a major component of ballistic coefficient as is bullet weight.
we talk drag to see what happens to b.c. at different velocities, as drag changes.
we have already discussed this mostly in relation to transonic flight here.
formulae used in ballistic programmes take this into account, and can also include spindrift in a deflection calculation.
there is little point in studying the flight of a 22 rimfire bullet out near 1000 yds because being so light it has a very low b.c.
this is why it has the same deflection at 200 yds as our bullets much further out.
if you want to start doing a calculation for a 45 cal bullet with a money or elliptical will be around 0.5. you can refine that from shooting drop tests.
the things that determine deflection are b.c. and velocity in the bullet and wind direction and strength atmospherically.
bruce.
trying to understand the subject in hand will be far more fruitful than looking for fault with insufficient understanding.
the gain for energy spent will be much greater.
bruce.
ventum est amicus meus
rgchristensen
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Re: Is Faster or slower generally best?

Post by rgchristensen »

All these matters that are currently our subjects of discussion (I won't say "debate") were worked out empirically by Metford and Halford about 150 years ago, and were reduced to precisely-calculable aerodynamic terms nearly 100 years ago. The ODG's didn't have our luxury of "sighter shots", therefore many carried thermometers, psychrometers, and barometers in their shooting kits, the information from which enabled them to get their first shot on target.

CHRIS
rgchristensen
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Re: Is Faster or slower generally best?

Post by rgchristensen »

All these matters that are currently our subjects of discussion (I won't say "debate") were worked out empirically by Metford and Halford about 150 years ago, and were reduced to precisely-calculable aerodynamic terms nearly 100 years ago. The ODG's didn't have our luxury of "sighter shots", therefore many carried thermometers, psychrometers, and barometers in their shooting kits, the information from which enabled them to get their first shot on target.

CHRIS
gunlaker
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Re: Is Faster or slower generally best?

Post by gunlaker »

I will add one thing to this discussion. I've seen it mentioned here a hundred times that the BC of our cast bullets mysteriously changes during flight from the firing line to the 1000 yard line.

There is exactly one reason for this. None of the drag tables used for any of the standard projectiles ( G1, G7.. ) matches the drag for our bullets. That's all. If someone were to spend the money to accurately determine the drag function for any of our bullets the BC would just be 1.0 from muzzle until it fell to the ground

The "G" tables were really useful before the age of the digital computer, and are a little but useful when comparing two bullets. When computing trajectories for modern jacketed bullets, you generally don't just read the BC from the bullet box. You select the bullet type and the software uses the known drag table for it rather than a BC number. No one number can ever describe the differences between a given projectile and a "standard projectile". BC is a barely useful approximation.

Chris.
mdeland
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Re: Is Faster or slower generally best?

Post by mdeland »

When I said the bullets change when fired I am referring to bump up and some folks believe the nose can slump off co-axis which would change BC. They are always shorter for the same weight when fired. Good discussion folks , much to consider and think about.
gunlaker
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Re: Is Faster or slower generally best?

Post by gunlaker »

mdeland wrote: Tue Aug 25, 2020 12:47 pm When I said the bullets change when fired I am referring to bump up and some folks believe the nose can slump off co-axis which would change BC. They are always shorter for the same weight when fired. Good discussion folks , much to consider and think about.
Yeah if there are wobbling or instabilty problems then the drag will definitely change between shots :-).

Chris.
bruce m
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Re: Is Faster or slower generally best?

Post by bruce m »

chris,
drag definitely changes with velocity, a fact that is mot obvious during transonic flight.
what drag model you use makes no difference to this.
hence b.c. must vary.
dan theodore used to talk about the 900 yd syndrome, where things could go a bit haywire.
this is the range where our best bullets are coming out of the transonic zone.
firing tests with the same bullet nose but progressively shorter bullets has proven that this problem goes away as the bullet shortens, thus increasing stability.
it is my belief that stability danger is at its greatest at the bottom end of transonic velocity as drag stops decreasing and either plateaus ir starts increasing again. this based on the bullets i have used only.
while on the subject of dan, grease grooves must affect drag, because his mini groove bullets shot flatter than big grooves, and micro minis flatter again.
kurt's term "speed humps" is a good one.
comparing the flight predictions of a programme of the same bullet using g1 and g7 shows some difference in drop, but surprisingly little.
an example of this is that where a g7 might put a boat tail bullet in the centre of a a plma target, the g1 will still prput it in the bull but not centre.
this shows that boat tails do not make a huge difference to drag, but do some.
greater gains can be had by lengthening and streamling the nose.
our cast bullets can only sustain a certain nose length.
these are the sort of areas that need a lot of money thrown at them, but it won't happen.
mike,
you are right about calculating the b.c. of a bullet from measurements in cast bullets.
they do shorten prior to leaving the muzzle, and it is the b.c of what comes out of the barrel that counts.
hence the preference for harder alloys in long range target bullets.
they slump less and hence retain more b.c.
slump can easily be compared with pp bullets by studying confetti.
the harder the alloy the less far forward you need to patch to just cut to the front of the patch.
however you have to start somewhere and refine with testing, both patch length and sight settings.
once you have some sight settings and a muzzle velocity, you have a b.c. available.
just be aware that it will be a different b.c. in transonic, before, and after.
bruce.
ventum est amicus meus
gunlaker
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Re: Is Faster or slower generally best?

Post by gunlaker »

Bruce the ballistics coefficient is just a fudge factor that describes how a given bullet's drag varies from the drag function of one of the various "standard" bullets. The drag as a function of velocity is captured by the drag function not the ballistics coefficient. Drag definitely varies as a function of the velocity, but that information can only be captured as a function, not a single scalar value which is all a ballistic coefficient is. I think that is why there is so much confusion and misinformation that continues to grow about our cast bullets being somehow magically unpredictable.

If the U.S. government decided to spend the money to measure the drag function for our bullets then you could build a simulation that would use a BC of precisely 1.0. i.e. no fudge factor. As another example, think of what a simulation would use for a projectile that was exactly the same as the "standard G1" projectile. It's BC would be exactly 1.0 at all velocities, but only because the drag function matches the bullet properly. This is why when you use software like JBM ballistics you can select the bullet and ignore the BC. It just uses a modified drag table as BC is irrelevant when you have the correct drag table.

Chris.
beltfed
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Re: Is Faster or slower generally best?

Post by beltfed »

A bullet does not Have to slump or set back.
Here are some of my 371 DDEPP( 2 diameter bullets that Kurt A snow shot last winter.
Bullets were fired with full loads and a 40-70SS and a 40-65.
Bullets are exactly the same length and form as cast. They only just have rifling marks on the "patch to groove" base band.
The patch to bore body just rides on the lands an so was not engraved since it does not upset/bump up,
Alloy: 9+1 COWW/Lino
about 15bhn
They will fly straight and accurate out to 1K from my 40-65 /16 twist.
And the "BC" /Drag function will only change due to velocity loss , not from setback/slumping,etc


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