By Emil Albertini (02389@fnma.com)
10/20/95
This article attempts to assist those interested in chronographs
understand how they are used and some of the features of three popular
chronographs available today. Also, I have included some (limited)
first hand experience regarding my recent acquisition and use of my
first chronograph.
While this article is a survey of some of the current availabilities, I
suggest that prospective purchasers obtain and read the information
available from the manufacturers before making a purchase. The
brochures contain valuable information.
I would like to point out that I am neither a statistical expert or an
engineer, so whatever you read here are the interpretations and
experiences of a somewhat non-technical person.
The contents are:
I. BACKGROUND AND BASICS
II. CHRONOGRAPH TYPES AND CATEGORIES
III. SUMMARY OF THREE MODELS
OEHLER RESEARCH (800.531.5125)
PACT, INC. (800.722.8462)
SHOOTING CHRONY (416.276.6292)
IV. MY EXPERIENCE WITH THE PACT MODEL 1 CHRONOGRAPH
//Emil
________________________________________________________________________
I. BACKGROUND AND BASICS
________________________________________________________________________
WHAT'S A CHRONOGRAPH USED FOR AND WHY DO I NEED ONE?
A chronograph measures the speed of an object such as a bullet or a
pellet or an arrow, passing through it's sensing field. If it is set near
the muzzle of a rifle, it measures muzzle velocity. Generally, all
bullets are measured near the muzzle - actually about 8 ft. - 12 ft. in
front of it.
Measuring the muzzle velocity can be important for many reasons,
including finding consistent (i.e. more accurate) loads, determining
potential (relative) high pressure situations, evaluating likely
erosion and barrel wear, and determining/plotting trajectories and
bullet drop for various down range distances.
HOW DOES IT WORK?
A chronograph includes three essential parts to handle input, computing
and output. The input devices are called skyscreens (early electronic chronographs used real metal screens as sensing devices) and the projectile
is shot over (across) a small defined sensing field above the skyscreens.
The computing device is a timer that measures the time it takes the
projectile to cover the sensing distance (2 feet - 4 feet). The output
device can be an LED display, a paper or tape printer, or computer memory.
A start and a stop gate are provided to trigger the clocking of the
object. The chronos reviewed herein all utilize light-sensitive
sensors that detect then amplify a drop in the light level when the
projectile passes over it to trigger the start and stop gate circuits.
The skyscreens are placed a precise distance (i.e., 24 inches) apart
and the chronograph is calibrated for that distance. Any error in the
placement distance can be extrapolated to the velocity, such that
placing the screens 0.5" further apart would result in about a 2% error
(lower) in the readout.
The computer converts the start and stop times to feet per second
measurement and sends it to the display or printer. The computer also
calculates other statistics about the shot string (discussed below).
Depending on the features of the chorongraph, is is possible for the
velocity and the shot number in the string to display only on the LED
display and/or print to a hardcopy readout as well as being stored in
memory for further statistical analysis.
Other components needed or that might be usefrl and might or might not
be included with a chronograph are:
Sky screen mounting bar, usually with a 1/4" X 20 tpi receptacle
for a standard (U.S.) camera tripod mount. (Usually optional but
built into remote units).
Sky screen diffusers to define the shooting area and partially
screen out too much light. (Usually provided with skyscreens).
Cables to attach the skyscreens to the local unit (provided).
Carrying case (usually optional or user provided).
Notebook, pre-printed data sheets, extra batteries, etc. (User
provided).
WHAT OTHER INFORMATION IS PROVIDED BY A CHRONOGRAPH AND HOW IS IT USED?
Besides providing the velocity for the last shot fired, when the
shooter has concluded a string of shots - 1, 2, 5, 10 ,etc. - other
statistics are calculated, and displayed, usually including:
1. High velocity
2. Low velocity
3. Extreme spread (high minus low)
4. Average (mean) velocity
5. Standard deviation (from the mean)
** NOTE: A technical or statistics based discussion of standard
deviation (SD) is available in an excellent article in the
NRA Handloading Manual (now out of print but still
available at gun book dealers). The article is out
dated in its description of equipment, but the
statistics portion is very good and I recommend reading
it. In fact, I recommend acquiring Handloading for many of
its articles and information, much which is not readily
available elsewhere.
Some chronographs store the data for future downloading to a PC and/or
include exterior ballistics programs to allow the plotting of down
range performance for a selected bullet, given the stored results.
Depending on the user's objectives, needs, and requirements, the data is
used in various ways. For instance, a target shooter who wants the
most accurate load is less concerned about eking the highest attainable
(safely) velocity out of his loads than he is with the consistency of
the shot to shot velocity (within acceptable velocity ranges, of
course). Therefore, the standard deviation of the string is his
primary concern, and his focus is on as small a number as possible,
meaning that the load is "consistent" in his gun. On the other hand, a
hunter might want to assure that he is attaining acceptable velocity
and in turn energy to assure that he is making clean kills at all
acceptable ranges and to calculate the trajectory of his bullet at
various ranges to give him sighting information. The varmint hunter,
on the other hand , might be concerned about both the foregoing,
wanting to achieve acceptable accuracy at the highest attainable
velocity to gain a good "flat" shooting load for plunking prairie
critters several football field distances away.
While the chronograph might not provide all the data needed, it
certainly is the first step in achieving any of these objectives. It
is also a far sight better than the "published" data for reloads and
factory loads that were measured under (usually) much different
interior and exterior conditions.
___________________________________________________________________
II. CHRONOGRAPH TYPES AND CATEGORIES ___________________________________________________________________
I would categorize chronographs into groups by four attributes or
features, including:
1. Local/remote read out
2. Printing/nonprinting results
3. Downloadable memory/volatile memory
4. Ballistics program/simple statistics
Let's review each of these major features.
1. LOCAL VS. REMOTE READ OUT
Obviously, the more components included in a unit, the more expensive
it is to manufacture. One way to reduce the components is to put the
skyscreens and the computer in one unit. The skyscreens mount on top
of the unit and the readout display is on the front panel. In my
estimation, this has two major drawbacks: shooting over (at) a
sensitive unit and the need to get up and walk out to the unit to read
it or to use binoculars to read the display. Regarding the former,
many of these units have been (unintentionally ?) hit and destroyed by
a low shot. In fact, I have an acquaintance who shot his chronograph
with the very first shot he tried to measure. With respect to the
latter, walking in front of the shooting line when others are on the
range is ill-advised and not allowed in most organized shooting
places. Therefore, one is left with using binoculars to read the data
and if it needs to be reset, the simple act of pushing a button on the
front panel has to wait until the line is clear and it is safe to walk
out to the unit.
2. PRINTING:
Printing v. non-printing seems pretty straight forward, but the media
and connections differ. Not having to copy down the velocity of each
shot and or shot string at the range is obviously a nice feature and
some users simply staple the tape to the related target, keeping all
the information in one place.
Because all these units are battery powered, energy consumption must be
conserved. Therefore, the units tend to be pretty small. Two paper
types include thermal (more expensive) paper and the traditional
"adding machine" or cash register plain paper tape. Printer units tend
to be built in, but some use an IR signal to transmit to the printer.
Obviously, printing capability increases the cost of the chronograph,
whether the printer is internal or external.
3. DOWNLOADABLE MEMORY:
As an alternative to printing out the results at the range or copying
them down on output sheets, some units have non-volatile memory that
permits the user to carry the unit home, plug it into a PC and dump the
data for storage, printing or further analysis and manipulation. The
standard connection seems to be a serial interface port. Data is
dumped out in various formats, usually compatible with a separate
program sold by the vendor or others such as RCBS.
4. BALLISTICS PROGRAMS:
Evaluating the velocity data in a ballistics program adds more
dimensions to its use, as discussed above. Some units include this
feature internally in the unit or in a separate program that runs on a
PC. In the case of the latter, the data must be downloaded or
otherwise input into a PC. The advantage of a PC based program is that
it does not inhibit the user of a low level, non-memory type
chronograph from further evaluating the data gathered at the range and
copied to a notebook. Then, too, one can always compare the results of
the internal program to that of an external/PC based program, getting
the best of both worlds.
________________________________________________________________________
III. SUMMARY OF THREE MODELS
________________________________________________________________________
There seem to be three popular makers of chronographs available in the
U.S., today:
OEHLER RESEARCH 800.531.5125
PACT, INC. 800.722.8462
SHOOTING CHRONY 416.276.6292
OEHLER RESEARCH
This company has been in the chronograph business at least as long
as I have been reading shooting magazines: thirty years or more. They
make the most sophisticated units and have the most impressive catalog
- more than 40 pages. A good portion includes at least six re-prints
of product reviews by various shooting sports related magazines such as
American Rifleman, Shooting Times, Guns & Ammo, etc. These make
interesting, if not informative reading for potential buyers of
chronographs.
Oehler's "bread and butter" model is the Model 35 Proof Chronograph
available with or without a printer. Oehler also offers a Ballistics
Explorer external ballistics program for IBM compatible computers.
Model 35 Features:
The "star" of the Oehler line up is what they call a "proof channel",
essentially a second timer and a third sky screen. The idea is to
make two measurements of the velocity and compare them to validate the
reading. It is not unusual for shots to go unrecorded as light
conditions and other factors influence the reading. The proof channel
helps weed out "bad" readings.
Otherwise, the 35 provides an LCD or printed statistical data readout
of high, low, extreme spread, mean and standard deviation. It also
shows shot-by-shot information regarding the shot number and channel one
velocity and channel two (proof) velocity. Controls include:
edit/reset, omit, and step/summary. The skyscreens and mounting
bracket are included in the price.
Prices:
Model 35 + two screens (no proof capability) $195
Model 35 P + three screens $225
Model 35 P + three screens +
built-in plain paper printer $345
Model 43 Features: Basic starts at $600
The more recent Model 43 ballistics laboratory type instrument that
provides statistics included in the Model 35 plus the capability to
measure (relative) chamber pressure and calculate interior and exterior
ballistics, including: velocity, b.c. point of impact, group size, wind
deflection, downrange energy, time of flight, drop and more (according
to the literature). It requires permanently fixing a strain gauge
sensor and wire lead to the under side of the barrel to take the
readings.
Model 82 Features: Basic set up starts at $7,500 and it is suitable for
tanks.
PACT, INC
PACT has not been around as long as Oehler and (I think) got its start
making timers for competition shooting. Now, they offer three types of
products for shooters, including: timers, chronographs and electronic
scales.
The PACT chronographs include three models: Model 1, PC and
Professional. Each includes the standard statistical data, including,
shot-to-shot velocity, and string data, including: high, low, extreme
spread, mean, standard deviation and average deviation. As
explained by the PACT people, standard deviation is used to predict the
velocity of the next shot while average deviation tells the shooter
about the shots already fired. You take it from there.
All the PACT models include their M5 skyscreens. The skyscreen
mounting bar ($25) and soft carrying case ($16) are optional.
PACT Professional: ($280)
PACT calls this their fourth generation chronograph and the "ultimate
chronograph system". It includes ballistics software to calculate
bullet trajectory. This can be done from chronographed data or entered
via the key pad to play "what if" scenarios of load, bullet, etc.
Memory also allows the user to chronograph his or her loads then run
the trajectories at home. It does this based on a built in library of
bullet ballistic coefficients for Barnes, Hornady, Nosler, Remington,
Sierra, and Speer bullets.
PACT PC2: ($180)
Basically, it includes the same chronograph features as Professional and
most of the down range trajectory information. It does not include a
printer, the memory is smaller, and the bullet library is not included.
The chronograph data for shot strings can be held in non-volatile memory
and down loaded back home to a PC. It is compatible with the RCBS PC
Bullet program.
PACT Model 1: ($130)
PACT refers to this chronograph as a third generation chronograph and
says it is comparable to the Oehler 35. It provides basic shot and
string data on a four digit display in strings of up to 24 shots.
Memory is volatile. An optional IR printer is available. The M5
Skyscreens are included and the carrying case and screen mounting bar
are optional.
SHOOTING CHRONY
"Chrony", as it is popularly known, seems to be the low price provider
in the market. Their model line up has been changing and, I think, as
more shooters become comfortable with using computers in their work and
leisure, these shooters are looking to buy more sophisticated equipment
- like chronographs. I get the feeling that Chrony is feeding this new
"mass" market with affordable equipment.
From the sales literature and ads I seen this year (1995), it seems
that Chrony's current line-up includes four models: Delta, Alpha, Beta,
and Gamma, each with progressively more features. The prices are from
the 1995 Mid-South Shooters Supply catalog, except for the Delta.
Chrony seems to be the only one of the three manufacturers outlined
here whose products at discounts from the MSRP.
Delta: Basic per shot data and string average; no s.d. or extreme
spread. ($55)
Alpha: Includes string s.d. and extreme spread; holds up to 32 shots in
memory. ($61)
Beta: Stores up to 60 shots; downloadable memory to PC. ($76)
Gamma: Ballistics program also downloadable to PC; timer; 1,000 shot
memory. ($140)
Accessories: Indoor Shooting Light Fixture: $23
Carrying Case: $15
All the Chrony models are all-in-one remote units in that the
'lectronics are out there under the skyscreens. I know fellows who use
them and feel that they are good value for the money. They also like
the all-in-one feature because there are no cables to deal with and it
is a very compact unit to carry to the range.
Please also see VII.C.10.a. Shooting Chrony Beta Model Chonograph for more chronograph information.
________________________________________________________________________
IV. MY EXPERIENCE WITH THE PACT MODEL 1 CHRONOGRAPH
________________________________________________________________________
SELECTION DECISION:
I reviewed the available information from Oehler, PACT, and Shooting
Chrony before deciding to purchase the PACT Model 1. I chose the Model
1 as a compromise between price and features, not wanting to invest
heavily in features that I was not sure I would use. Basically, my
need for a chronograph was peaked by my desire not to use too hot
loads in my M-1 Garand because of the fragile nature of the Garand op
rod. My secondary and tertiary reasons were for development of
consistent loads and to test performance of various pellets in my
several different pellet guns.
I rejected all the Shooting Chrony models because of the remote
design. I knew at least one person (and had heard of others) who had
shot their Chrony machines. Also, I was turned off by the need to read
the display from ten feet away with a pair of binoculars. I was
already carrying too much equipment to the range, including a spotting
scope and I didn't want to added more pieces.
I did not go for a higher end unit with a built in ballistics software
because I can acquire these capabilities when needed on a PC and enter
the chronograph information myself.
I rejected the need for a printer because I planned to use only the
basic features of velocity and shot string statistics and to do the
recording manually. I do not plan or intend to sell velocity
information or time on the chronograph at the range. My time there is
precious little and I guard it. I developed some data sheets for 10
shot strings and simply jot the data on the sheet after I've concluded
the string.
DESCRIPTION OF THE PACT MODEL 1:
The unit is fairly small (2.25" high, 5.0" wide and 5.25" long). The
display is easy to use and the controls are simple. The leads to the
skyscreens are about 15 feet long and pretty sturdy. The plugs are
generous, also, and don't slip out of the jacks. The leads are
permanently attached to the skyscreens at the other end of the wire
which is a little inconvenient and makes stowing the unit more
difficult. It would be nice if the cables could be detached from the
skyscreens.
My unit included the sky screen mounting bar and chronograph case for
the price of the chronograph, including shipping. While the
electronics and display box are `light as a feather`, the skyscreen
mounting bar is made of two pieces of 1/2 inch square tubing, attached
together with welded cross pieces. The top, at the ends of the tubing,
are drilled and tapped for four sky screen mounting screws, each, and
the mid-piece is drilled and tapped for a standard camera tripod
attachment screw (1/4" X 20 tpi). It's painted a nice pretty red.
The skyscreens attach to the mounting bar with screws. An angled
plastic diffuser upright bracket slips into a slot on either side of
the sky screen, making a flat bottom "vee". Then, a bowed white light
diffuser attaches to the two uprights, forming an arc over the sky
screen. Under low light conditions, PACT suggests removing the
diffusers. The brackets provide a convenient "sight" for aligning the
skyscreens with the target. The sensing area above the screens is
plenty large enough to permit shooting at a couple of SR targets set
side-by-side at 100 yards.
The skyscreens require four screws to attach them. I elected to put
'em on the bar and leave them there. Therefore, I needed a bigger box
to store the bar and screens so I built one to house the electronic
unit, diffusers, extra batteries, notebook, pencils, etc. I divided
the box along its length to protect the skyscreens (mounted on the bar)
from the other loose stuff (diffusers, brackets, batteries, etc.) that
might move about in there. It's a good way to transport the unit and a
better way to store it, but it is awfully bulky and a pain to tote from
the car to the range. In fact (and this is a little embarrassing) I
now have so much gear to take to the range (guns, tool/equipment box,
ammo/sand bag box, chronograph box, tripod, targets, lunch) that I have
resorted to using a sturdy luggage carrier with 3" wheels to haul it
from the parking lot to the benches!
PACT recommends setting the skyscreens at least 8 feet from the muzzle
to avoid having the shadow of the blast trigger the start clock,
causing errors or erroneous readings.
They also describe how at low sun angle, late in the day, the underside
of the bullet can reflect light onto the sky screen causing the bullet
to appear brighter, not darker, than the surrounding light and fail to
trigger the chronograph. I thought that this would be very unusual,
but I did indeed experience this problem on my first chronograph outing
on a late afternoon. I did get some non-reads as the sun was shining
into my face and the front of the skyscreens from about fifteen degrees
left and very low on the horizon. I think I clipped a couple of used
targets to the left side of the diffuser uprights and that solved the
problem.
I have also used the Model 1 to clock pellets in my basement as well as
bullets from various rifles at the high power range. I have not used
it with pistol loads, but expect no problems.
Using the chronograph indoors is an eye opener and a great way to try it
out without taking up valuable time at the range experimenting.
Initially, it would not give any readings using the overhead
incandescent and fluorescent lights in the garage. A call to PACT
solved the problem: add more light; a lot more. They suggested
suspending at least a 75 watt light 12 inches above each sky screen. I
used two large reflector work lights with clamps on the base and
attached them to a board suspended above the skyscreens so the light
shined directly onto the skyscreens with the diffusers removed. I
clocked ten shots from each of my six pellet guns without one error.
A friend who has a Model 1, and incidentally whose experience I relied
on when selecting PACT and this unit, uses it for chronographing arrow
speeds without problems, too.
PACT addresses the question: "how do I know if my unit is accurate?"
which was definitely on my mind. They suggest using a fairly well
established load to test consistency of the chronograph, recommending
Eley Tenex .22 ammo that has an established velocity in rifles of
approximately 1080 fps. In my .22 rifle with a 22 inch barrel, ten
shots of Tenex produce an average velocity of 1072 fps. Close enough
for me. I plan to carry the rifle and clock at least five rounds of
Tenex at the start of each session.
A chronograph also opens the door for much experimentation and testing,
that is otherwise only conjecture, opening up new avenues of discovery
for shooters and reloaders by providing the capability to compare loads
head-to-head. For instance, I want to measure the effect of primer
pocket uniforming and flash hole deburring on velocity consistency. I
intend to test this effect ( using 60 cases nearly uniform in weight),
holding the sizing, length, primer, powder, bullet and seating depth
constant and load four batches of 15 cases each as follows:
Batch 1: No deburring, no uniforming.
Batch 2: Deburred only.
Batch 3: Uniformed only.
Batch 4: Deburred and uniformed.
This test might not do much for most readers or reloaders, but it sure
peaks my interest. Others might be more interested in measuring the
effects on consistency derived from varying primers, bullets, load,
powder. All are valid and achievable with a chronograph.
HINDSIGHT:
I am happy with the Model 1 and feel that I have made a good choice
with this unit. It provides the information I want in a format that I
can use. Of course a printer would be nice, but I like to keep it
simple and jotting down the shot data and stats forces me to allow the
barrel to cool a little between shots, too.
The unit definitely adds to the pile of gear already being carried to
the range. There is also set up and take-down time for the
chronograph, tripod, skyscreens, etc. Figure about 10-15 minutes at
each end of the session.
One surprising "side effect" was the number of on-lookers who wanted to
know what it was, how it worked (o.k., we're not such a sophisticated
bunch at our club) and then came the inevitable question: "could you
test my loads for me"?
Now, I wasn't prepared for this last one and had not even thought about
it. I definitely didn't want anyone shooting over my new and somewhat
delicate equipment, but I didn't want to do the shooting with unknown
loads. I also didn't want to be a jerk and refuse to share my
equipment (shooters don't treat shooters that way) but then, I also
didn't want to spend the valuable little time I had at the range
clocking everyone else's loads. Because the first request came from a
14 year old, I acquiesced and put five shots out of his rifle and over
the skyscreens for him and gave him the results on a clean form after I
jotted them down.
In the future, I plan to address such requests as follows: "I'll be
happy to clock your loads when I am finished with my shooting and
chronographing, as time permits". This seems like a fair compromise; I
get done what I came to do and if the requestor wants to wait until I
am finished, that's fine.
Also, I understand that some people charge for chronographing loads
which likely turns some away. I didn't buy my chronograph to make
money or to pay for itself. If I take it out for our club's annual
sight-in days, I might consider charging and turning over the proceeds
to the club. I'm still worried about who does the shooting over my
equipment and the soundness of the piece being tested and the safety of
the loads therein, especially reloads.
SUMMARY
A chronograph adds a new dimension to shooting and answers a lot of
questions about muzzle velocity and consistency that are otherwise next
to impossible to address. As the cost of electronics has fallen, more
chronograph companies have come into the market in recent years. The
prices of all units I have seen are reasonable and much less than the
price of a scope or a new stock. I suggest that anyone contemplating
buying a chronograph first review the features of the available units
and read all that is available.
Because chronographs are not quite as ubiquitous as the ads portray,
actually trying one before buying is still difficult. Therefore, I
would be happy to answer any questions readers might have about the
information included here.
I also want to thank my r.g shooting buddy, Martin Olsen, for taking up
his valuable time to review this article and provide his considerable
comments.
I can be reached via email at two addresses:
emil@fnma.com
72072.706@compuserve.com
Regards and happy shooting!
Emil Albertini