Mark Sims wrote:

The fact that the direction in which the last 4" of the barrel largely
determines the initial trajectory of the bullet (in absence of crosswind
etc) was made use of to assist in alignment of the sights during mass
production of infantry rifles during WWII.

Bruce

Could you be more specific, and perhaps provide a reference?

Paul Mauser's group was pretty fussy about sighting through the
new barrels, and bending them a little here and there to make sure
their bores were perfectly straight.  The WWII records on the M1 Garand
talk of using a bore scope to adjust the adjustible iron sights.
The WWII records on the M1 Carbine talk of the same technique.

-Chuck Harris

Bruce Griffiths wrote:

Chuck

It was a paper written around 1942 detailing the procedures used to
align the sights of mass produced rifles for which it was impractical to
have each rifle individually adjusted on a firing range.
Unfortunately I dont think I have a copy of this any longer, however
I'll keep an eye out for it.
The alignment jig used a mirror attached to a cylindrical plug that was
a close slip fit into the end of the bore.
It wasn't perfect but far better than not adjusting the sights at all.

Bruce

Chuck Harris wrote:

If I recall correctly, the article was published in the Journal of the
Optical Society of America around that time or perhaps a little later.

Bruce Griffiths wrote:

I've remembered that I was originally looking for DD Maksutov's article
on his catadioptric telescope published in 1944.
Consequently I had a look at the contents of JOSA for 1944 and I believe
the actual article in question is:

An Optical Sighting Gauge for the Garand Rifle C. B. SITTERSON and JR.
and NORMAN F. BARNES, JOSA, Vol. 34, Iss. 3, pp. 126–126 (1944):
http://www.opticsinfobase.org/josa/issue.cfm?volume=34&issue=3
http://www.opticsinfobase.org/josa/issue.cfm?volume=34&issue=3

It was probably intended more as an acceptance test by the army.

Bruce

Bruce Griffiths wrote:

Hi Bruce,

Thanks for the reference.

Bore sights are a system that I use, and I find they work very well.

Some how I misread your initial post in a way that lead me to believe
that you were saying the barrel was being bent to adjust it to target.

Upon re-reading your post, I cannot for the life of me figure out how
I could have gotten that impression from what you wrote... Sorry!

-Chuck Harris

Bruce Griffiths wrote:

On Tue, 23 Dec 2008 08:36:57 +1300, Bruce Griffiths
bruce.griffiths@xtra.co.nz wrote:

since we have so many shooting time nuts here, I thought that y'all would
enjoy this page:

http://www.neon-john.com/Misc/Antique_Chrono.htm

I bought this instrument new in the box at an estate sale.  The guy apparently
acquired it but never even cut the packing tape from the box.

It works perfectly, using the wire-break principle.  I made some screens by
gluing a few runs fine copper wire across the bull's eye to paper targets. The
display is transit time.  The velocity must be looked up on charts that
convert the time and the screen spacing into velocity.  I actually wrote a
little HP41 program to do that and dispense with the charts.

Unlike my Oehler and its sky screens, it is not fooled by shock waves
(sub-sonic rounds) or debris (shotgun shells) and is very repeatable.  The
velocity results agree within reasonable statistics of my Oehler 33p.

One of these days when the round tuits become plentiful, I'm going to design a
little box to interface the Oehler skyscreens to this unit.

I also have one of Oehler's very first commercial chronos.  It's all analog
and uses the constant current/capacitor method of determining time-of-flight
and displays the results on an analog meter.  Again, it appears to use the
wire-break method (no manual).

John

John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Democracy is three wolves and one sheep voting on what to have for supper.

Cool.  I used systems like this (but a bit faster) for measuring
detonation velocity in explosives.  Several wires would run through an
explosive compound and would break as the material detonated.  Later
the systems used the same wires but would measure the voltage/current
running through them as the explosive detonated in a magnetic field.

-Bob

On Mon, Dec 22, 2008 at 4:37 PM, Neon John jgd@johngsbbq.com wrote:

And for the ham time-nuts, Hiram Percy Maxim's father invented the
Maxim machine gun.  Hiram Percy Maxim invented the firearm silencer.

-Chuck Harris

Brooke Clarke wrote:

Points of pride, I'm sure.

-- Dave

Chuck Harris wrote:

David M. Witten II skrev:

All this talk still does not make me feel like going out and get a
firearm of any sort, fashinating as they can be in their own right.

If someone got me involved in elk-hunting maybe, but that's about it I
think.

My intent is to get some stuff done in the lab during the vacation.
(Desperatly trying to get some more on-topic discussions going).

Cheers,
Magnus

Magnus Danielson wrote:

Here are two questions that have been running around my head:

1. Following on from the discussion last week about trying to
   synchronize multiple oscillators to improve phase noise, I've wondered
   about a simpler tack:  take, for example, two 5 MHz atomic standards and
   mix their outputs together, using the 10 MHz result to drive a time
   scale.  Assuming the standards were of relatively equal quality, would
   this provide a better time scale than using one of the standards alone?

2. Several measurement techniques require a given phase relationship
   (e.g., quadrature) between DUT and reference.  For HF frequencies (ie, 5
   or 10 MHz) is there a practical phase shifter design covering 180+
   degrees that doesn't involve switching various lengths of coax in and
   out of the line?

Happy holidays!

John

Surely, you don't have a problem with a precision trombone line for 10 MHz, do you?
You could use a water dielectric and slow the waves WAY down so it's of practical length (if not impractical in other ways)

But more seriously.. How accurate and stable does the phase shift have to be?  There are some little 10MHz phase shifters down in one of our labs that are (guessing) some sort of transformer inside.  They're about the size of the Helipot style 10 turns (i.e. a couple inches in diameter and a couple or three inches long, with a 1/4" shaft to adjust phase. (I'll go down and see if I can find one and the mfr & part #.. They're probably not made any more, though)

A more classic approach is to take a 2x or 4x frequency and run it into a suitable divider/decoder to generate quadrature.

Once you have quadrature, you then need some way to combine the two with varying amplitudes.. Sine/cosine pots, etc  Or some MDACs driven by a lookup table.  (the commercial phase shifters use a 90degree hybrid and some sort of variable gain thing.. PIN diodes, mixers, what-have-you)

Some form of goniometer springs to mind as a way to do it.  The stability of couplings, etc., are going to be determined by mechanical tolerances, and clever design might make it fairly temperature immune.  Vacuum capacitors are quite stable with aging (since the dielectric doesn't change)

James Lux, P.E.
Task Manager, SOMD Software Defined Radios
Flight Communications Systems Section
Jet Propulsion Laboratory
4800 Oak Grove Drive, Mail Stop 161-213
Pasadena, CA, 91109
+1(818)354-2075 phone
+1(818)393-6875 fax

John Ackermann N8UR skrev:

I have been looking at mutual lock systems for say two 10 MHz
oscillators. This mutual lock system behaves much as a PLL circuit (as
contrary to the other mutual lock methods described previous) such that
a phase detector detects the phase-difference between the oscillators, a
loop filter filters this difference and then it is feed back with
opposite signs to the respective oscillator. I envision that a common
EFC input exists to the system. Such a system is kind of interesting in
that within the PLL bandwidth, the two oscillators are locked and you
see the average of frequency errors etc. Well above the PLL bandwidth
the two oscillators is independent of each other and just above the PLL
bandwidth they are essentially independent. As the two oscillators is
phase-locked in, their outputs can be combined and noise reduction can
be achived, which is the significant effect above the PLL bandwidth.

It is interesting to notice that the PLL operates on the difference
between the oscillators, where as the EFC input is acting as a common
mode action, which in the perfect world is not influenced by the
diffrential PLL. Realities is however such that the EFC is not linear,
and the need to regulate differently also ensures that the oscillator
gain constant never really match, and therefore will also the
diffrential PLL "leak-in" on the common mode behaviour.

I have not seen any reference to this type of diffrential PLL action to
mutual locking. I've only seen discussions on mutual locking involving
injection locking.

This diffrential locking technique could be applied to atomic standards,
but then naturally require much improved solution than simple
oscillators. The diffrential locking technique does not magically solve
issues that is typically common mode, such as temperature dependence. It
can however even out individual properties like noise and systematic
drift to some extent. It essentially runs the oscillators as a common
constellation and attempts to achieve the average improvements of those
oscillators in an interlocked fashion. In its simplicity it will do
unweighed averaging. It is fairly easy to do weighed averaging by
individualizing the feedback gain to the respective oscillators. Further
refinements would individualize the proportional and integrate feedback
terms, but as always, the simplicity forms a limit.

I have intended to make some runs just for fun to see how this behaves
in real life.

I wish you all happy holidays!

Cheers,
Magnus

David M. Witten II wrote:

ABSOLUTELY!  Freedom was born of guns.

Tyrants are never willing to give it to you
without a fight.

-Chuck Harris

This is similar to the problems of synchronizing multiple AC generators connected to a common bus. In that application, you typically adjust the throttle on the prime mover (or penstock gate for hydro) for each generator, while keeping a stable system frequency.  This is a very difficult problem because of the nonlinearity and time delays inherent in the system, not to mention the fact that there's transmission lines involved and a varying load.  The transients on long transmission paths (like from pacific northwest to southern California) can take many hours to die out.

There have been notorious oscillation issues in days of yore.. Modern GPS disciplined frequency references makes it easier.. (rather than sync to each other, you all sync to a common master) As do DC links with inverters.

In your case, you're trying to do the mutual synchronization scheme.

Jim

Magnus Danielson wrote:

Assuming that the atomic standards are correct for some tolerance of
"correct", I'm not sure why you would need to use a differential locking
scheme (or anything else that moves one oscillator versus the other) --
if you simply mix the two signals together you get a sum that contains
both signals.  Apart from redundancy (what if one unit fails), why not
just use that sum to drive the clock?

John