Ballistic coefficients of pellets?
Rog
are less than 0.1, and airgun pellets are generally much less then
that. Is there a program (or listed mathematical approach) to
determine an airgun pellet's BC in order to calculate drop?
VT
Staright Shooters do velocity tests with various pellets and show the
measured BC of the those pellets.
Their tests seem to indicate that the BC of the same pellet varies
with the airgun that it's shot out of.
See the velocity tests under each individual airgun from their "Our
Take" tests:
http://www.straightshooters.com/genmenus/ourtake.html
--
Vincent
remove CLOTHES when replying
Dave Remling
Cardew raised an interesting question. Does a pellet keep it's shape when
fired. particularly from magnum spring guns. this could account for the
variability seen.
Perhaps a test with a hard pellet, such as a CP, v a softer pellet in spring
and PCP guns may yield an answer.
"VT" <vtvi...@prodigyCLOTHES.net> wrote in message
news:3d1c7afc...@news.prodigy.net...
Rusty Hinge
from "Dave Remling" <drem...@nycap.rr.com> contains these words:
> Cardew raised an interesting question. Does a pellet keep it's shape when
> fired. particularly from magnum spring guns. this could account for the
> variability seen.
> Perhaps a test with a hard pellet, such as a CP, v a softer pellet in spring
> and PCP guns may yield an answer.
Depends on the power of the gun. A bit of experimenting (On an
authorised range) with an early .22 pump gun import (not regulated)
allowed you to pump until you couldn't move the lever any more.
At about 50 strokes using a punched and formed pellet the head was
blown off and the skirt left in the breech.
A .22 short bullet and 100 strokes resulted in ž" penetration of a
piece of plywood at 10 yards. (That is, the bullet broke right through a
piece of ž" ply - but only just.)
--
Rusty
This space not left blank in case someone nicks it before I've found a
good sig.
http://www.users.zetnet.co.uk/hi-fi/tqt.htm
Dave Remling
those Asian repeater pumps that once pumped can provide several shots. I
have an old Sheridan 8 pumps is max supposedly, I have gotten 10 in without
valve lock. This will clear 1 inch pine board using cylindrical (pointed)
pellets. There are folks who will modify it to provide in excess of 20
fpe - not bad for a gun that goes under 5 lbs.
I think Cardew was referring to the possible deformation resulting from the
sharp slap a spring gun gives the pellet. Pneumatic acceleration is assumed
to be less violent.
On another note, my 707 easily sends pellets clear through 2x4 pine studs.
My ..177 M48 19 fpe - before I detuned it - would break out the back of a
piece of 3/4 plywood but not quite exit the board. THIS WITH CP lites, a
hard pellet.
I live in the Peoples Republic of NY, my range is my back yard . Been
playing with some valve modes on a Crosman 2240 CO2 pistol. It would have
required a FAC before I started and is well into the 7FPE range now - with
the stock barrel.
I would like to know if anyone has ever set up 3 or more chronographs and
measured the same pellet's velocity at different ranges. seems to me that
this would eliminate one layer of averaging, helping to sort out the
differences between spring and pneumatic propelled pellets of the same
muzzle velocity. Not that the data would probably cause any major change in
the pellet gun world, just that it would be nice to have a definitive
answer.
"Rusty Hinge" <tqt.h...@sheddiknights.org> wrote in message
news:200207020...@sheddiknights.org...
> The message <fv4U8.79379$uk2.31...@twister.nyroc.rr.com>
> from "Dave Remling" <drem...@nycap.rr.com> contains these words:
>
> > Cardew raised an interesting question. Does a pellet keep it's shape
when
> > fired. particularly from magnum spring guns. this could account for
the
> > variability seen.
>
> > Perhaps a test with a hard pellet, such as a CP, v a softer pellet in
spring
> > and PCP guns may yield an answer.
>
> Depends on the power of the gun. A bit of experimenting (On an
> authorised range) with an early .22 pump gun import (not regulated)
> allowed you to pump until you couldn't move the lever any more.
>
> At about 50 strokes using a punched and formed pellet the head was
> blown off and the skirt left in the breech.
>
> A .22 short bullet and 100 strokes resulted in พ" penetration of a
> piece of plywood at 10 yards. (That is, the bullet broke right through a
> piece of พ" ply - but only just.)
VT
<drem...@nycap.rr.com> wrote:
>Vincent:
>
>Cardew raised an interesting question. Does a pellet keep it's shape when
>fired. particularly from magnum spring guns. this could account for the
>variability seen.
>
>Perhaps a test with a hard pellet, such as a CP, v a softer pellet in spring
>and PCP guns may yield an answer.
>
Dave,
I don't know for sure about that - however taking some of the figures
for a "harder" pellet like the Crosman Premier:
It seems as though the BC of any given pellet can actually vary with
the gun that it is shot out of - ie: it is not a constant for a given
weight and shape as I initially thought - at least this is what I've
gleaned from looking at the velocity test results from Straight
Shooter's "Our Take"
- just as an example:
Crosman Premier .22cal @14.3gr BC
Springers
= 0.022 - Webley Stingray (12fpe @ muzzle)
= 0.025 - RWS 34 (12fpe)
= 0.026 - BSA SuperSport (15fpe)
= 0.028 - RWS 48 (19fpe)
= 0.026 - RWS 52 (20fpe)
= 0.026 - Beeman Kodiak (24fpe)
= 0.021 - Beeman Crow Magnum III (26fpe)
PCP
= 0.018 - FX-Tarantula (28fpe)
= 0.025 - BSA Super 12 (23fpe)
= 0.023 - BSA Spitfire (18fpe)
The BC can vary from 0.018 to 0.028 for the Crosman Premier .22cal -
and the CP is one of the most consistent pellets
.177cal Crosman Premier Heavy @ 10.5gr BC
Springers
0.026 Beeman R7 6FP
0.026 Beeman R7 9FP
0.021 Webley Stingray 11FP
0.024 BSA SuperSport 11FP
0.027 RWS/Diana 34 12FP
0.031 Beeman R9 13FP
0.031 Beeman R1 15FP
PCP
0.024 FX Tarantula 17FP
0.023 Falcon (FN19?) 14FP
So you can see that the BC for the Crosman Premier Heavy .177cal @
10.5gr can vary between 0.021 to 0.031 - that is quite a difference!!
All results taken from Straight Shooters "Our Take" -
http://www.straightshooters.com/genmenus/ourtake.html
These BCs I believe are calculated/derived from actual velocity
measurements at the muzzle and downrange at a set distance.
So perhaps the BC for any pellet is not a constant but varies with the
gun used (notice the BC is also different even from guns of similar
energy/velocity ratings) ?
Rusty Hinge
from "Dave Remling" <drem...@nycap.rr.com> contains these words:
> Interesting, What was the make/model of the pump gun? Sounds like one of
> those Asian repeater pumps that once pumped can provide several shots. I
> have an old Sheridan 8 pumps is max supposedly, I have gotten 10 in without
> valve lock. This will clear 1 inch pine board using cylindrical (pointed)
> pellets. There are folks who will modify it to provide in excess of 20
> fpe - not bad for a gun that goes under 5 lbs.
Don't remember, but ISTR it was Japanese.
> I think Cardew was referring to the possible deformation resulting from the
> sharp slap a spring gun gives the pellet. Pneumatic acceleration is assumed
> to be less violent.
Is it? I'd have thought that the acceleration imparted by a moving
piston would begin to move the pellet at a low pressure, building up to
a maximum and to be much gentler than the sudden release of maximum
pressure while the pellet is stationary.
> On another note, my 707 easily sends pellets clear through 2x4 pine studs.
> My ..177 M48 19 fpe - before I detuned it - would break out the back of a
> piece of 3/4 plywood but not quite exit the board. THIS WITH CP lites, a
> hard pellet.
Using pointed pellets the pump rifle would put a hole through two
sheets of corrugated steel at around ten yards. Can't remember how many
pumps that was.
Dave Remling
the first 6 inches of barrel.
Effect has two principal constituents, the use of the gas as an energy
transfer medium and the burning of trace amounts of lube in higher power
guns. The pellet has been shown not to move until just before the piston
rebounds. The effect is similar to whacking a croquet ball
in contract, pneumatics depend upon a more prolonged push to speed up the
pellet. the more gentle the acceleration the less likely the deformation.
Their book is a good read and well worth purchasing if you have interest in
how airguns work.
Dave Remling
Vincent, this is precisely my point. the BCs are so small and to my
knowledge a correct form factor to base them on was never developed. As BCs
are determined as deviations from standard ballistic forms, and were
developed to simplify very complex calculations, the lack of a suitable form
casts doubt upon the validity of the exercise.
There is also another problem with the methodology that I assume was used,
shooting strings with the same pellet and gun at different ranges -
statistics...
If one measures the performance of a single projectile at several points,
one will have a set of data about that single shot. If one measures one
shot at the muzzle another at 10 meters, another at 20... one ends up with
several groups of velocities from different pellets, different populations.
One must use statistics to correlate this data and arrive at a determination
about the validity of the data. It is my experience that the use of the
common 10 shot string allows for a lot of statistical ambiguity.
To prove my point, a while back I shot 10 10 shot strings from a BSA Meteor
one of the strings , the second, had an unusually hot shot, followed by a
cold one - typical small diesel and starved following shot.
I put all these strings in a spreadsheet and calculated their Standard
deviations, I then also calculated SDs for all rows and both diagonals as
well as for the full 100 shots. this gave 23 different SDs for the same
data...
SDs ranged from 6.36 to 106. even throwing out the obviously bad numbers
( and technically this may not be a valid thing to do) the high was 12.66
and the low 5.49 the average SD with the 2 wild shots removed was 9.84
with them in it was 34.42.
Given an average SD of 9.84fps that means that 65% of all shots will be
within 1 SD of the average velocity, 95% within 2 SD ... If you had selected
the 6.36 SD or the 12.66 SD the impacts on your calculations would have been
very significant. As you can see, trying to measure any small differences
in velocity with a small sample size is very difficult as the true
variations will be left in the noise. Trying to infer differences in
performance by comparing averages of different strings is probably
statistically invalid. the results probably show more noise than data.
I am not a statistician,, but for these small sample sizes, I believe the
student t method rather than the standard deviation formula should be used.
Depending upon the curve chosen, the percentages of the population found
within 1 SD can be much smaller.
I believe that one way to get around the measurement problem while still
keeping the number of shots on a manageable scale is measure the velocity of
each projectile at each necessary point. thus you only have one population
to deal with. with somewhere between 100 and 1000 shots at each initial
velocity you could develop some statistically valid data. Of course, you
may have to sample at several different initial velocities...
VT
Dave,
BC figures are small - but it is the number of significant figures or
"precision" that counts - since BC is a calculated or derived figure
rather than one thatb is measured directly.
I would agree that measuring the velocities of a single shot at set
distances would be the "correct" way of doing things.
However I think that taking the average of a string of shots at the
set distances is less correct - but also valid - as long as truly
abnormal readings are accounted for (eg: discarded), and the standard
deviation is stated.
Your SDs were absolute figures - translate that into % (percentage)
figures - then apply the standard deviation/error to the calculated
BC figures and you will see that BCs percentage differences/error
would be in the same magnitude and the SD of the calculated BC in
absolute figures will be "small" - ie: all this is just saying one has
to deal with % figures.
I think that even allowing for the standard deviation of velocity
strings and using the opposites (ie: worst case) the variation in the
calculated/derived BC would still be within meaningful experimental
errors -
ie: not be as wide/wild as the 48%-55% differences that the Straight
Shooters readings gave.
(eg: BC can vary from 0.018 to 0.028 for the Crosman Premier .22cal
which is 55% difference;
and BC for the Crosman Premier Heavy .177cal @ 10.5gr can vary between
0.021 to 0.031 which is 48%)
Dave Remling
good hearing from you.
the issue of SD has become somewhat of an irritant to me. basically because
many data in the shooting sports are developed with 10, 5 or even 3 shot
samples, which simply don't provide a broad enough sample size to support
the accuracy claimed. People tend to latch on to numbers and use them in
invalid ways producing invalid results. (I am also on a school board and
the uses that some of the standardized testing is put is a REAL CAUTION -
but this is another subject, not to get me started.... I did go so far as
to check out a few books on statistics and try to educate myself...)
Perhaps the data are stringent enough to allow true calculations. As I said
I am not a statistician. However, the issue of not having a form factor
developed specifically for pellets and projectiles that function similarly
is still a problem. It is my understanding that a BC is really a simplified
deviation from the calculated performance of an "ideal" form. If an ideal
form does not exist for airgun projectiles, then the deviations must have
been calculated from a form that probably does not truly reflect pellet
aerodynamics. This being the case, I would expect to see significant
deviations just owing to the different drag at different velocities.
back to statistics.
I did a fairly detailed test of an IZH61 a few years back to determine the
best pellets and whether there was a difference between the plastic and
metal clips. Although it appeared that the metal clips were better (and
most serious shooters seem to agree) the results were not statistically
significant, as Bryan Targett, of Stalker, pointed out. If anyone knows
about performance I would believe it to be Stalker - If I had a few grand
laying around..... check their site.....
I suspect that this is the way it is with a lot of development, particularly
with devices as complex as airguns. there are so many variables that it is
very difficult to get statistically significant results for many
developments. Not to say the developments are not functional, but BCs are
predictive values and if their underlying basis is faulty they will not
function as designed.
Personally, I don't use them,, given the cost and range of airgun shooting,
I follow Ian's Pelant's advice.
"VT" <vtvi...@prodigyCLOTHES.net> wrote in message
news:3d232fca...@news.prodigy.net...
Rog
methods of calculation used for ordinary projectiles. For classical
bullet styles cross-sectional densities, ogive shape and other
physical features can be plugged into an equation, but for an
arbitrary projectile such as a pellet, round ball or dart, BC can
still be determined by either having a measurement of drop points or
two velocities with a known distance between measurements. I think
it's a transcendental or recursive problem, so cannot be expressed as
a closed-form solution, but there are a number of programs available.
Would like very much to see the source listing (in BASIC or anything
else) for one of these programs, it can't be all that difficult, can
it?
VT
<drem...@nycap.rr.com> wrote:
>the issue of SD has become somewhat of an irritant to me. basically because
>many data in the shooting sports are developed with 10, 5 or even 3 shot
>samples, which simply don't provide a broad enough sample size to support
>the accuracy claimed. People tend to latch on to numbers and use them in
>invalid ways producing invalid results.
Yes, there is a great danger of quantifying whatever is there to
quantify - even if the figures are invalid and taking those as
"gospel".
However I think you probably have personally done enough chronograph
testing of airgun to know that the muzzle velocity of a reasonably
functioning airgun is not going to vary by large percentages.
Around 10fps in a (low'ish) MV of 500fps is only a 2% deviation.
Taking this worst case figure (since most of us can recognize an
abnormal shot such as dieselling/detonation) and allowing for the BC
say to be proportional to the square of the velocity - then the
expected variance can at maximum be only about 4% (1.02squared) - even
allowing for a cubed relationship then the max variance would be in
the ballpark of 6% - to get a 50% variance in BC as in the Straight
Shooters results that would have to have a exponential relationship to
the power of 20!!! ie: (1.02)**20 = 1.50 - I know that airgun pellet
ballistics/BC is complex - but to the power of 20 of a velocity??
I cannot disagree that much experimetal results could be questioned
and some figures cannot be relied on as rigorous scintific or
statistically correct -
But the point that I was making is that the BC results/measurements at
Straight Shooters on pellets show significant variance far beyond mere
experimental error
- ie: even for a reputed consistent quality pellet such as the Crosman
Premier - BC can vary by as much as 55% - when the expected variance
in muzzle velocity is closer to about 2%
Dave Remling
damned if I would be able to do the math. but there may be a way to check on
these figures. Catch the pellet.
A large change in BC must show up as a change in the physical shape of the
projectile...
stands to reason if the pellets can be caught carefully without damage
their measurements before and after should show differences for different
guns.
I have given a little thought to how to accomplish this. I think that some
fine polly stuffing, as found in pillows, etc, may allow a gentle
deceleration while padding the pellet...
The only tools needed would be a chrony and a micrometer.
It won't give a BC, but I suspect that large BC changes, if real, should
show up as different deformations.
I wonder how difficult it is going to be to dig the pellet out of the fiber
for each shot?
I would postulate that a high spring gun would be most likely to cause
deformation.
VT
well from those BC figures -
CP in .22cal
= 0.026 - BSA SuperSport (15fpe)
= 0.026 - Beeman Kodiak (24fpe)
same BC figures from springer airguns differing in power by 60%
(that's huge)
But then:
same CP .22cal in PCPs (less likely to deform?)
= 0.018 - FX-Tarantula (28fpe)
= 0.025 - BSA Super 12 (23fpe)
variance of BC of 39% for "similar" power differing by 22%
CPH .177cal 10.5gr
0.021 Webley Stingray 11FP
0.031 Beeman R9 13FP
0.031 Beeman R1 15FP
variance of BC by 48% for springers differing by 18%
yet using one of the same airguns
0.031 Beeman R9 13FP
0.031 Beeman R1 15FP
the same BC for a similar difference in power of about 15%
As for Catching the pellets -
(1) good luck :)
(2) deep tank of water? - shooting downwards of course - I think
that's how many ballistic labs use to recover bullets for examination.
Rog
long tubes of damp sawdust. Water is not suitable, nor is gelatine.
Shooting various pellets into bars of Ivory soap, even after
penetrating as many as six bars I was unable to measure with precision
calipers any increase in the head diameter of Crossman Premiers (22
cal) having an initial velocity of 900 FPS out of a Falcon SS. I also
failed to detect mushrooming from any of 14 different 177 pellets shot
from my R1 into soap, again with an approximate 900 FPS muzzle
velocity. Silver Bear and Crow Magnum hollow-pointed pellets were not
tested.
On Fri, 05 Jul 2002 04:57:25 GMT, vtvi...@prodigyCLOTHES.net (VT)
wrote:
Rog
long tubes of damp sawdust. Water is not suitable, nor is gelatine.
Shooting various pellets into bars of Ivory soap, even after
penetrating as many as six bars I was unable to measure with precision
calipers any increase in the head diameter of Crossman Premiers (22
cal) having an initial velocity of 900 FPS out of a Falcon SS. I also
failed to detect mushrooming from any of 14 different 177 pellets shot
from my R1 into soap, again with an approximate 900 FPS muzzle
velocity. Silver Bear and Crow Magnum hollow-pointed pellets were not
tested.
On Fri, 05 Jul 2002 04:57:25 GMT, vtvi...@prodigyCLOTHES.net (VT)
wrote:
>Pellet deformation?
VT
>Ballistics experts and precision benchrest shooters capture rounds in
>long tubes of damp sawdust. Water is not suitable, nor is gelatine.
Thanks for that - about what length of damp sawdust is needed to
safely capture an airgun pellet in the range of 10-15fpe muzzle energy
uisng .22cal pellets?
Does it make a difference with different calibers, like .177cal .20cal
and .25cal?
>Shooting various pellets into bars of Ivory soap, even after
>penetrating as many as six bars I was unable to measure with precision
>calipers any increase in the head diameter of Crossman Premiers (22
>cal) having an initial velocity of 900 FPS out of a Falcon SS.
This is interesting - thanks again
So even after hitting bars of soap the pellets failed to show any
deformation. - in the case of the Falcon SS with .22cal CPs at 900fps
that's about 26fpe muzzle energy.
> I also
>failed to detect mushrooming from any of 14 different 177 pellets shot
>from my R1 into soap, again with an approximate 900 FPS muzzle
>velocity.
>Silver Bear and Crow Magnum hollow-pointed pellets were not
>tested.
>
I've shot pellets into Plumber's Putty
with airg-rifles of about ~13fpe (a BSA SuperSport in .22cal) and
about ~9.5fpe (Crosman 2260 co2 air-rifle .22cal)
and air-pistols of about 3.4fpe (Webley Tempest .22cal) and ~5.6fpe
(Crosman 2240 co2 .22cal air-pistol)
RWS Super-H(ollow) Points .22cal -
all the power levels show some degree of deformation - obviously with
the ~3.4fpe Tempest almost minimal - but noticable. All the way to the
~13fpe BSA SuperSport where the rear skirt/body completely breaks
through the head to leave the head as a ring of lead. The ~9.5fpe
Crosman 2260 the deformation is quite substantial where the head is
starting to turn inside out.
Copperhead Wadcutters .22cal
show flattening of the head to a larger diameter and quite noticable
shortening of the total length in both the BSA SuperSport and Crosman
2260. On the Crosman 2240 this just noticably obvious - on the Tempest
it is barely noticable.
Crosman Premier .22cal
there is a slight shortening of the pellet length in the BSA
SuperSport and only just noticable on the Crosman 2260 - but no
noticable expansion as such.
Copperhead Pointed .22cal
very similar to the CPs in .22cal
Obviously Plumber's Putty is a different media to Ivory soap bars -
how this corrolates to actual live quarry has not been established
Dave Remling
Assuming that the pellets from the same lot are reasonably identical and a
proper form factor has been established, then something must alter their
shape to account large differences in BC.
If the shape changes - I would look at:
compression, therotically I believe a shorter pellet will have more
drag,
Diameter. breaches and choked barrels
rifling marks. I have noticed a marked difference in groove count,
depth and width between different manufacturers.
to this end I just acquired some material that I will use to try and arrest
pellets without deformation.
Of course, haveing an incorrect form factor or testing methodology can also
contrubute to the differences. I am unaware of similar BC variance in
handloads. My handbooks make no note of it, nor have I found reference to
BC shift in other material.
As stated earlier I strongly suspect the use of an incorrect form factor -
pellets are a high drag projectile, expremental error, and possible pellet
deformation play a part. If I can not show significant deformation, then
what is left but form factor and expermental error?
Unfortunatly, for the purpose of this experment, my collection is fairly
eclictic. I doubt I will have similar barreled guns so comparing the same
barrel at different power levels in a springer, will be out. While I can do
some expermentation in pneumatics, my Sheridan is a 20 can and my 707 a 22
which makes .177 testing difficult. I haven't started testing yet, but my
guess is that If I am able to develop a method of catching pellets without
deformation I will be lucky. Well time will tell.
Another possible culpret is precession, posisblly caused by a nicked crown.
Cardew was unable to show precession in their experments, but I have seen
high speed films of cannon that do precess.
Do you have any other ideas that might account for the findings?
Dave Remling
stuffed toys and sleeping bags. my hope is that the initial srtike will
carry fibers and these will accrete increasing the frontal area and bleeding
of the energy slowly.
I will report on my findings when I have some results.
I use duct seal, a heavy form of plumbers putty, myself in my indoor
backstop.
Rog
substantial deformation in flight that would contribute to substantial
changes in BC. However, since magnum air rifles can now approach
muzzle velocities that are near (and even beyond) the speed of sound,
care must be taken to allow for this, since BC is a nonlinear function
of bullet velocity, particularly in the transonic region. Arbitrary
projectiles such as airgun pellets are most effectively analyzed by
measuring a velocity V1 near the muzzle and another V2 downrange.
Knowing the distance S between measurement points and having V1 and
V2, the average value of the BC is simply S/(F1 - F2) where F1 and F2
are the values for the space function corresponding to V1 and V2
respectively. Hatchers' Notebook (a handloader's reference) contains
a lookup table for space functions based on the values of Mayevski
ballistic functions. Another way to do this might be to curve-fit the
values in the Notebook to create an easy-to-use closed form solution.
This should work well for subsonic calculations at least, but for
greater accuracy you might want to estimate the "breakpoints" of 790,
970 and 1230 FPS (the Mayevski Functions were all obtained empirically
- there are no sharply defined breakpoints). In any case, the most
valuable BC is probably derived from measurements made over the
approximate range actually used, since these changes in BC are thus
factored in and averaged.
If there are large published differences in BC for pellets that are
outwardly similar, it might be related to how the above procedure was
managed. Since it's to the advantage of the pellet maker to claim the
highest ballistic coefficient possible, this might encourage
measurements being made at the higher near-sonic velocities closer to
the muzzle. They may also have just guessed at it - or perhaps lied.
Those who have made the two-velocity BC measurements have derived BCs
that are substantially identical to published values (regardless of
the gun used), and that's understandable, since that's how the
manufacturers did it.
-Rog
Dave Remling
You seem to have a background in math or similar. I am not so inclined. so
perhaps the equation you offered makes sense, but where is the idealized
shape? is it part of f1 and f2? Can you point me in the direction of a
definitive, but readable text on ballistics? Diff Equations was quite a
while back and not my best course...
I have a copy of Hatchers, but it has been a while since I read it. I will
give it a look.
my basic issue is that if pellets do exhibit different BCs for different
guns, them something must be different. If not the pellet, then most likely
it is caused by experimental error of one kind or another or the use of
incorrect formula.
I believe that a ballistic coefficient is not an absolute, but a fudge
factor to show the deviation from the performance of one of a number of
ideal shapes. As most ideal shapes were designed for firearms or cannon
they do not exhibit the performance characteristics of high drag projectiles
of low sectional density. Could it be that if plotted against a standard
shape of correct characteristics that the variances would shrink?
This morning I had an idea. I am going to try and make a wind tunnel and
see if there is a notable difference between fired and unfired pellets. I
figure to use a 2 foot piece of 1/2 inch EMT and an aircompressor. I will
blow down into the tube and place a pellet. balanced on a piece of piano
wire in the bottom 2 inches. the length of tube should allow the flow to
smooth some. the piano wire will extend down through a board to a powder
scale below.
I think that this discussion may become a little deep for this list. please
contact me directly if interested in continuing this discussion. If i do
develop anything of interest I will probably place it in the airgun forum
where it will reach a broader segment.
"Rog" <Ro...@hotmail.com> wrote in message
news:m4ugiukuqtc082ri3...@4ax.com...
BruceHP
<drem...@nycap.rr.com> writes:
>I have a copy of Hatchers, but it has been a while since I read it. I will
>give it a look.
>
If you have a copy of Hatcher;s formula and two crono's you can just enter V1
and V2 and forget all of the tables and and foofy BC stuff!
-----====================================================
Keep Shooting!
Bruce
InterNet: Bruce.Pe...@comp-online.com
RIME : ->495 AOL: Bru...@aol.com
===================================
BruceHP
<Roger...@hotmail.com> writes:
>BCs are small (<0.2) for pellets, but there are evidently several
>methods of calculation used for ordinary projectiles.
B.C.'s are really only of historical signifance. They were needed when you
couldn't measure the velocity of any thing at two different measured
distances. Now you just buy two crono's!
BruceHP
<drem...@nycap.rr.com> writes:
>stands to reason if the pellets can be caught carefully without damage
>their measurements before and after should show differences for different
>guns.
Try a large pipe filled with water. Put a short elbow at the far end so you
can reach in to get the pellet. Angle the pipe slightly so the water doesn't
run out.
BruceHP
(VT) writes:
>BC figures are small - but it is the number of significant figures or
>"precision" that counts - since BC is a calculated or derived figure
>rather than one thatb is measured directly.
My guess is that you will need at least 5 places (.xxxxx) to calulate any
usable data using the BC programs.
BruceHP
<drem...@nycap.rr.com> writes:
>I would like to know if anyone has ever set up 3 or more chronographs and
>measured the same pellet's velocity at different ranges. seems to me that
>this would eliminate one layer of averaging, helping to sort out the
>differences between spring and pneumatic propelled pellets of the same
>muzzle velocity. Not that the data would probably cause any major change in
>the pellet gun world, just that it would be nice to have a definitive
>answer.
I have done this. In most cases the pneumatic does far less damage th the
pellet, thus it will have a better BC,
BruceHP
<drem...@nycap.rr.com> writes:
>Cardew raised an interesting question. Does a pellet keep it's shape when
>fired. particularly from magnum spring guns. this could account for the
>variability seen.
>
>Perhaps a test with a hard pellet, such as a CP, v a softer pellet in spring
>and PCP guns may yield an answer.
>
Of course it changes its shape. The faster the pressure peak and the softer
the skirtL the more the pellet will act like a wadcutter. (blown-out skirt)
BruceHP
<drem...@nycap.rr.com> writes:
>I believe that one way to get around the measurement problem while still
>keeping the number of shots on a manageable scale is measure the velocity of
>each projectile at each necessary point. thus you only have one population
>to deal with. with somewhere between 100 and 1000 shots at each initial
>velocity you could develop some statistically valid data. Of course, you
>may have to sample at several different initial velocities...
>
Measuring the velocity at two or more points for each shot and then calculating
the BC for each shot then averaging that string will give a decent number.
Actually you never need to calculate a "B.C." anyway. Once you know the
velocity at two points you don't need any more data to calculate the drop of
that pellet.
Rog
Suggest you find a copy of "FSI Advanced Airgun Ballistics" by F. S.
Brychta. I obtained my copy from Firearms & Supplies Inc.
www.AirgunsUSA.com
As I recall the book was $25.97 USD.
-Rog
art69
Rog
wrote:
>On Mon, 01 Jul 2002 22:14:35 GMT, "Dave Remling"
><drem...@nycap.rr.com> wrote:
>
>>Vincent:
>>
>>Cardew raised an interesting question. Does a pellet keep it's shape when
>>fired. particularly from magnum spring guns. this could account for the
>>variability seen.
>>
>>Perhaps a test with a hard pellet, such as a CP, v a softer pellet in spring
>>and PCP guns may yield an answer.
>>
>
>Dave,
>
>I don't know for sure about that - however taking some of the figures
>for a "harder" pellet like the Crosman Premier:
>
>It seems as though the BC of any given pellet can actually vary with
>the gun that it is shot out of - ie: it is not a constant for a given
>weight and shape as I initially thought - at least this is what I've
>gleaned from looking at the velocity test results from Straight
>Shooter's "Our Take"
As you have observed, BC is not a constant value and should not be
expected to be. BC is a function of many variables apart from the
projectile's form and weight, and these must be accounted for in its
calculation. The mathematical models of Mayevski (that were used to
create Ingall's Tables in Hatcher's Notebook) were actually based on
experimental data for six velocity ranges, with particular detail
given to the transonic region. Take a look at the chart shown at:
http://home.snafu.de/l.moeller/Mayewski.html
This clearly shows the problems that can occur when attempting to
predict BC without considering velocity, since there is a clear
dependence. Even at 900 FPS you can see that retardation is becoming
nonlinear, and at higher velocities moreso. For ordinary bullets,
things are much more predictable, since muzzle velocities and bullet
form factors are fairly consistent for a particular round. However,
since PCPs often have variable power settings, it should be clear that
BC can only be defined for a single setting, and is also likely to
vary from gun to gun, depending on muzzle velocity (particularly with
higher-powered rifles).
-Rog
Dave Remling
tables.
For my personal use. I generally sight in a gun with a particular pellet
that does well in it and that is that. From a pragmatic approach, it works
quite well.
I went back over some micrographs I had taken of IZH61 engraving on a series
of pellets. there are some noteable differences. I also recovered a CP
lite shot from a M48. It had a lot of engeaving on it's head as well as
skirt. the RWS gun really chews on a pellet. There is a major difference
in pellet engraving between these two guns. Given the low mass of these
projectiles, I can see where the rifling marks may make a noticeable
difference in flight charactoristics.