From: sfaber@intgp1.att.com
Subject: Re: better chronograph
Organization: AT&T

From article <2aopgd$hgj@usenet.INS.CWRU.Edu>, by
gmk@falstaff.MAE.CWRU.EDU (Geoff Kotzar):

# In article <9310201242.AA01727@hpfcnews.fc.hp.com> bartb@fc.hp.com
# (Bart Bobbitt) writes:
#
# #Oheler chronographs tend to be the most accurate.  Their high-end models
# #are accurate to about 1 fps.  If your needs require velocity measurements
# #accurate enough to determine velocity standard deviations within 1 fps
# #below 10 fps, you'll need a chronograph with a 1 fps accuracy.
#
# You have stated similar things before regarding chrono accuracy,
# but as you know manufacturer claims often don't agree with reality.
# Also, 1 fps accuracy from a device with a maximum practical range of
# say 4000 fps comes out to about 0.025% which is very bloody good. In
# fact for most laboratory transducers 0.10% is considered very good
# performance and 0.025% would be truly excellent. This sounds like a
# claim based on clock rates alone and ignores all of the other factors
# that contribute to practical accuracy of the device.

The nice thing about the Oehlers is that it measures the same shot
twice, so you can look at the deviation of the difference between
the 2 shots and get an actual measurement of the precision of your
measurements.  Most of the time with a 4' screen distance, I have
seen a precision of 1 to 2 ft/sec.  Sometimes it is worse depending on
the light conditions.  If you go to an 8' screen distance it is
pretty easy to get a 1 fps std. deviation of error.
The absolute accuracy may be off more than that of course.

From: sfaber@intgp10.ih.att.com (-Faber,S.R.)
Subject: Re: Chronographs
Organization: AT&T

In article <3i8q6a$j3c@xring.cs.umd.edu>,
Don Kenny <dkenny@ix.netcom.com> wrote:

#I have been shooting & reloading for over 30 years, and have found the
#Oheler to be the finest chronograph.  First off, the Ohler has *TWO*
#chronograph circuits, so you always know about "false readings".  This
#feature alone makes PACT and all the other chronographs poor performers.
#The only problem is cost, as the Ohler goes for about $300.

You can get the Oehler for $225 without the printer and wire up a
particular Casio printing calculator to it for about $25 more if you
want to be cheap.

I just ran a test of a PACT in series with an Oehler 35(P).  I'll
post the detailed results later, but in summary the Oehler (4ft screen
distance) gave results self consisent to the proof screen to 1-2 ft/sec,
increasing to close to 3 (std.dev.) when the sun went pretty low.
This is shooting at a single target pretty low across the screens on a clear
day pretty late afternoon.
The PACT (2 ft screen distance) averaged 8 ft/sec higher readings with
a 5 ft/sec ave std deviation of the difference between the PACT and Oehler.
There was one data point out of 15 that was an outlier.

Steve

From: John De Armond
Newsgroups: rec.guns
Subject: Re: Opinions on Chronographs
Keywords: reloading, chronograph
Date: 1 Aug 89 16:57:27 GMT

In article <30676@ism780c.isc.com> john@wa3wbu.uu.net (John Gayman) writes:
>   I would like to solicite opinions on the various makes of chronographs.
>I've pretty much discounted the two popular models that place the
>display/controller down range with the skyscreens. Basically it looks
>like the Pact or Oehler 35P are the way to go. Prices (with printer)
>seems to be comparible. All I have to go on are the various reviews
>in the recent mags on the Oehler. They were are *very* favorable. If
>any of you have used either of these units I would appreciate hearing
>your opinions. Thanks.

I have a model 33 Oehler.  Several years old.  I am very pleased with the
unit, less so with the skyscreens.  I have the standard skyscreens that
came with it (skyscreen II, I believe).  These consist simply of a plastic
molding with a phototransistor inside.  They are fairly pickey about
sun angle and intensity.  You also have to shoot fairly close to them.
This invariably causes you to shoot one or more of them.  After the
second one, I machined replicas of the screens out of 1" boilerplate
designed to split along the centerline of the cell.  A spring arrangement
holds the parts together.  Now, if I shoot one, the assembly gets knocked
off the end of the stick, the pieces separate and fall away and the photo-
transistor is saved.  A little filing to remove the crater and you are
back in business.

I've had the opportunity to shoot over skyscreen IIIs.  They are better
but still not the solution, especially with scoped guns. With a scope,
spatial relationships are hard to judge.  In other words, it's hard to
tell when you've cleared the damn screen.

Electrically, the unit is very well designed.  IT has proper edge detection
which makes it extremely sensitive to even faint shadow signals.

The higher clock speeds of the newer units should make them more
accurate.  I'd not recommend taking advantage of this to reduce the
separation distance, however.  I use 4 feet which I consider to be a minimum.
I made a telescoping boom from square aluminum tubing (Ace Hardware) which
makes the thing much more transportable.  It is designed to mount on a
standard camera tripod.

Based on this experience, I'd expect the 35P to be a nice instrument.  After
using mine a couple of years, I think a printer is essential.  It is a real
pain in the butt to keep track of each reading, aim the gun and miss the
skyscreens.  If all I had to do is look at the display momentarily to make
sure the shot was recorded and not a flyer, my life would be much simpler.

John

From: John De Armond
Subject: Re: Chronographs
Date: 4 Jan 91 05:54:15 GMT
Organization: Rapid Deployment Systems (making go-fast things and things that-go fast)

bjb@hubcap.clemson.edu (BJ Backitis) writes:

>So, if anyone out there would be so kind as to suggest/recommend/comment
>on chronographs, I would really appreciate it.  I'll summarize e-mailed
>replies and post it here.  What I'm interested in is cost (how much ARE
>these puppies, anyway?), features to look for and/or avoid, and what are
>some good reliable brands?  Also, any recommendations for places to
>order them from (I haven't seen any listings in Shotgun News, except for
>one called Chrony... $80 or so).

I have an Ohler model 33 and have used the new Ohler printing chrono plus
I've used the Chrony and another put-'em-out-front-so-you-can-shoot-'em
type that I don't remember the brand name of.

The major tips I can state are:

1)	Avoid the ones that contain the integral skyscreens like the plague -
	that is unless you like to see bits of your chrono flying through
	the air after you shoot it.  You WILL shoot it, especially if you
	shoot a rifle with a medium to high power scope.

2)	Get the so-called sky screen II (Ohler's name) type skyscreens that 
	have optics over the photocells and a light diffuser above.  The bare 
	cell types, while they work, require you shoot so close over them
	that you'll invariably tag one.

3)	Get a printer if your budget can at all handle it.  It's a real 
	distraction to have to write down the readings after each shot.
	The new Ohler has an adequate printer.  One of the other brands
	uses the HP portable printer designed for their calculators.
	This is a very nice combo, as the communication between the printer
	and the chrono is via an infrared light beam.

4)	Make sure your chrono will calculate statistics.  Standard deviation
	is the bare minimum.  It should also calculate average and
	extreme spread.  SD is the most accurate indication of
	consistency in loading.  Extreme spread can indicate if you do
	something really wrong occasionally.  The chrono should also
	allow you to edit out "flyers" or bogus readings after the fact.
	Ohler will let you reject a reading after it is shot but you
	can't edit after the fact.

5)	The Ohler uses three screens and takes a second reading they call a
	"validation" reading.  After using one for awhile, I'm not sure I
	see a great benefit.  So far, every reading that has failed validation
	has appeared bogus on the face.  Example:  900 or 5000 fps on a
	round you know does about 2500 fps.  Unless you are very meticulous in
	placing the skyscreens, you can introduce errors due to different 
	distances between the main and validation screens.  This is especially
	true if you use a short separation.

6)	When you evaluate the unit, look to see how slow and how small a bullet
	it will reliably clock.  A good unit should reliably clock a BB gun
	and an arrow.  This is a measure of how well the pulse slicing 
	circuitry is designed in the unit.  Also check the operation in less
	than optimum lighting conditions.  My Ohler 33 is really picky about
	oblique and/or hazy lighting.  This again is a reflection of the 
	pulse slicers in the unit.

Opinions:

I don't at all like the genre of chronos typified by the chrony.  Their
flimsy construction and flimsy skyscreens mean that precision is not 
possible.  These are fine to check to see if your favorite popper 
load will make IPSC major but I would not try to do any serious load
development on one.  Plus you'll be guaranteed to shoot it up.

I've mainly used mine to develop bullseye loads for my Model 70 .30-06,
my NM M-1 and my silhouette pistols.  In the model 70 in particular,
velocity is critical for accuracy.  100 fps either side of optimum and
the group size grows.  What I've found with all my guns is that once
I find a velocity that is most accurate with a given bullet, I can change
powders and primers and brass and as long as I can work back to that
velocity, accuracy and point-of-impact will remain the same.

John

From: John De Armond
Subject: Re: Chrony chronographs
Organization: Dixie Communications Public Access.  The Mouth of the South.

cash@convex.com (Peter Cash) writes:

#Well, Midway has the Chrony chronographs on sale for $80, and I'm tempted.
#I realize that they don't have all the neat features of the more expensive
#Pact--but they are only a fraction of the price. So, I'd like to know: are
#the Chronys reasonably accurate, reliable, and useful?

If you just want numbers to satisfy your curiosity, the Chrony will
do fine.  IF you want accurate AND repeatable numbers that can be
compared over time and used for load development, look elsewhere.

The issue is the distance between the screen vs the length of the bullet.
These things work by detecting the shadow cast by the bullet as it
passes over the photocells.  The better sensors, such as Oehler's
limit the view of the cell to a narrow slice.  With fairly wide open
sensors such as on the Chrony, at what point in the building bullet shadow
the timing circuit triggers is dependent on a number of things including
temperature, battery voltage, lighting angle, shineyness of the bullet,
whether a shock wave passes before the bullet (subsonic round) and probably
a lot of stuff I've not thought of.

Oehler says that he does not consider a sensor spacing of under 4 feet
to be capable of sufficient accuracy for long term use.  His units
will work at under 4 feet and indeed come configured for 2 foot spacing
so it's not just a "buy mine because of this" syndrome.

One indication of chrono problems is if you shoot lots of rounds from
a factory lot and the standard deviation varies significantly.  While
the absolute SD will vary remarkably for similar loads, the variance
should NOT change within a lot.

I've experimented with chrono circuitry to connect to the parallel port
of the PC.  I've yet to come up with a better sensor and input
circuit than simply copying Oehler's.  (the 33 comes with a schematic on
the back cover of the manual.)  I am very impressed with the consistency
of my Model 35P, as I was with my Model 33 before.

John

From: John De Armond
Subject: Re: Chronographs - advice
Organization: Dixie Communications Public Access.  The Mouth of the South.

bobharbour@aol.com (BobHarbour) writes:

#I am looking at getting a chronograph and am trying to decide whether to get a
#PACT or an Oehler.
#I was told by one gentleman that the PACT model 1 indicated consistantly higher
#standard deviations than the Oehlers and hence that the Oehlers were more
#accurate than a PACT. I was planning to get the simplest model from the vendor
#decided on.  Does anybody have any experience with either or both of these
#beasts?

I had an Oehler 33 for over a decade and then upgraded to a 35P with the
proof screen setup.  The proof screen involves a 3rd skyscreen which
takes a second measurement of the bullet velocity.  The computer
compares the measurements and flags the reading if the two vary too
much.  Too much variance indicates a defective measurement.

This is one of those features that you don't realize you need until you
have it.  Using this chrono with loads that I've been using for years
has shown me that "spreaders"* recorded with the 33 are in reality
defective measurements.  The standard deviation of my pet loads
are now about where I thought they should be.

If you are a serious reloader who relies on the chrono for stable,
repeatable and reliable readings, you MUST have a 35.  I recommend
dropping the extra few bux for the printer option.  So much easier
to use.  If you're a casual reloader who uses the chrono just to see
whether your loads are duplicating those in the reloading manual or
to see if you make IPSC major or other similar uses, most any
chrono will do just fine.  But if you want to measure the effect
on standard deviation of a primer change or measure changes between
lots of primers or measure the effect of temperature on your load,
you really don't have any other option but to get a 35.

John

* "spreader" is the term I use for a reading that is not large enough
to be classified as a "flyer" and thus discarded but causes the
standard deviation and extreme spread to increase.

From: John De Armond
Subject: Re: Chronographs
Organization: Dixie Communications Public Access.  The Mouth of the South.

Doug White <gwhite@ll.mit.edu> writes:

#2) I want to compare prices with Oehler, but I can't find ANY of the major
#dealers that carry them.  Are they only available from the factory, or can
#someone recommend a good (preferably discounted) mail order source?  The
#prices on Pact seem fairly fixed in the catalogs that carry them.

Direct from Oehler only, as far as I know.  Give 'em a call at 512 327 6900
and ask 'em for a catalog.  Very interesting publication.  You'll probably
get to talk to Mr. Oehler himself because he usually answers the phone.

#The only info I can find on the different Oehler models was in a year old
#reloading handbook, and I haven't seen much more info on the Pacts.  Does
#anyone know if any of the gun rags have actually done a side-by-side
#comparison of the different models?  The $220 Pact claims that it also
#contains some sort of limited ballistics calculator, but they never say
#what it does, or how you use it.  The 3 screen Oehler sounds like a very
#nice machine, but for the amount I will be using it, I don't think I can
#justify the expense.  Unless I can get an Oehler with equivalent features
#for $300 or so, I think I'll probably end up with the Pact.

The Pact has a couple of interesting features including the ability
to drive the HP 82240 infrared printer (which means a PC interface
is pretty trivial) but for me the accuracy and reliability of the
Oehler 3 screen system makes the difference.  The Oehler 35p complete
with the printer is in the $330 range so you should be able to do it.

John