The “Mag Pal Speed Beez S&W Model 41 Clip Loader” from Amazon is a major aid to anyone with a Smith & Wesson Model 41 target pistol. Interestingly enough, this loader also works on Norinco TT Olympia target pistol magazines. Hope this helps someone out there.

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Sock Sorters

40 or 50 years ago there was a firm in Hong Kong manufacturing a small useful laundry accessory called a Sock Sorter. This was a one piece disk shaped clip designed to keep pairs of socks together during the laundry cycle.

The original, well designed product is on the left in brown. It is easy to use, with soft fingers that are easy on the socks. The original firm has long since gone by the wayside but other Chinese companies have picked up on this and are producing copies of a sort. Searching for “Sock Sorters” on Amazon brings up several. Unfortunately the copiers had apparently only seen pictures of the original and did not have physical access to samples. The copies appear to be made of polyethylene like the originals but have much stiffer fingers. The version in the center is more difficult to use and in the case of the item on the right in dark orange the result is too stiff and small to use with any but the thinnest of socks. In an effort to help any other budding entrepreneurs, herewith are the actual dimensions in inches:


Outside diameter 1.155

Finger Thickness 0.024

Ring Thickness 0.075

Inside diameter 0.922

Tip gap 0.179


Center (light orange):

Outside diameter 1.211

Finger Thickness 0.044

Ring Thickness 0.121

Inside diameter 0.970

Tip gap 0.181


Right (dark orange):

Outside diameter 1.103

Finger Thickness 0.042

Ring Thickness 0.121

Inside diameter 0.842

Tip gap 0.137


As an added benefit, the original at 0.466 grams uses 41% less material than the the 0.787 gram copy.

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Electronic Earmuff Noise

One ongoing source of annoyance is the omission of critical specifications by manufacturers. A prime example is electronic earmuff noise. This is the hissing sound that can be heard in most audio systems when you turn up the volume without other input and is dependent upon the design of the preamplifier circuit. Some common muffs have so much noise that the claim of being used to heighten hearing to detect quiet sounds is essentially meaningless. These also have a high enough noise level to be really annoying at volume levels suitable for range conversation. As a result you turn them off and gain nothing over cheaper passive muffs. This noise level could be specified in dB for a given condition just like the NRR rating or the maximum amplified level. Since it is not, it is impossible to tell before buying a pair whether or not the noise level is too high for usability. Unfortunately, even the low noise units do not specify this and are probably losing out on some sales as a result.

One example of the latter are the Honeywell Howard Leight Impact Sport (20dB NRR) and Impact Pro (30dB NRR) muffs. These are high quality muffs and are very quiet. At least the Pro says it can amplify animal sounds up to 5X. Both of these have similar low noise levels compared to some other brands. Once I discovered this using a friend’s pair, I bought two Impact Pro’s (one for the wife) and donated my existing electronic muffs.

My recommendation, if you are looking into electronic muffs, is either buy Howard Leight Impact Pro units or go to a sporting goods or firearms store in person where you can try out various brands.

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Time Constant (LAG) Final Value Predictor

In dynamic and control systems one of the most common elements is a lag. This is a first order slowing or delay of an action. It is generally modeled by a transfer from a constant potential to a storage element through a resistance. The key characteristic is that the rate of flow is proportional to the difference in potential between the source and the storage element. In electronics it is commonly charging a capacitor through a resistor from a constant voltage source. Other examples include: adding air to a tire from a constant pressure source, filling a water tank from the bottom using a constant pressure source, certain chemical reactions to equilibrium, spinning up a flywheel from a constant RPM drive through a fluid coupler, heat transfer by conduction from a constant temperature source to an object at a different temperature, or damped spring compression with a constant force. The response of these systems to a step change in potential looks like this:

Lag step response

Mathematically this response is the exponential shown below where b is the instantaneous value, f is the final value, t0 is the step time, T is the lag time constant, and t is the time variable. If you want to predict the future final value in a control system to speed up loop response time you have to sample three points and then solve these three equations to find f in real time. In the normal scheme of things this will involve calculating logarithms (inverse exponentials) which will take a lot of CPU time, time you may not have for a high speed control system. Here’s a surprising shortcut. If the three samples are at an equal time interval, typical of sampled data systems, you can finesse the transcendental functions and still get a mathematically exact solution. Equal time samples and the self-similarity of the exponential function allow the ugly stuff to cancel. The derivation of the solution follows.

Split and isolate the exponentials on one side.

Eliminate the common exponential term.

Eliminate the remaining exponential term by setting the fractions equal.

And solve for f. The final closed form solution has three multiplications, three subtractions, and one division, a much lower computational load for the control processor. One multiplication can be eliminated as shown in in the code sample.

Lag final value predictor performance. 1: Random input, 2: lag response, 3: Algorithm below run on the second line data in real time.

In the actual application the lag data is constantly sampled and processed. Each new sample takes the place of the oldest of three and the predicted value is recalculated allowing real time tracking as shown above. This algorithm was developed for a control system that needed to predict the final settling value of a temperature probe in a hot air stream. The thermal lag of the probe element inside its protective thermowell made the response much to slow to accurately keep the process temperature within limits.

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A Tale of Two 22s

During the recent government panic induced by China many entertainment venues, including my favorite bar, were shut down along with most of the economy. Some of the few activities available were the local gun ranges and I spent a fair amount of time shooting. With ammunition shortages and high prices, much of it was with 22 LR. My 22 rotation was a Ruger Mark II, a Bersa 224, and a Norinco TT-Olympia, all of which work very well and are not ammunition sensitive.

Later, when firearm availability improved I was looking for something additional like a 22 revolver and came across a slightly used Walther “Colt” Gold Cup Trophy target pistol which I purchased. I’ve also owned a Jonathan Arthur Ciener 1911A1 22LR conversion kit for a while, which I finally applied to one of my 1911’s. The Ciener was iffy with several failures to go into battery, failures to fire, and some failures to eject requiring a tap with a brass rod to remove the shell casing stuck in the chamber. The failures to fire could be fired by recocking the hammer and trying again. This was possible as the the Ciener and Walther retain the 1911 hammer. The Walther was worse with similar failures and even one detonation slightly out of battery that blew brass fragments out the ejection port. It was also very inaccurate for some reason. Now I knew why this was on the used market. Upon careful examination with a bore sized gauge I determined that there was a slight ring of lead about two thirds of the way down the barrel. A light dawned. Apparently the former owner had also experienced an out of battery ignition, that, unlike mine, stuck in the barrel. A subsequent shot cleared the blockage but not before swaging a ring of lead into the bore. I had been shooting through this existing restriction, distorting the projectiles, and causing the accuracy problems. I was able to restore the bore with an aluminum bore size scraper, lead solvent, and a fair amount of brushing. This fixed the accuracy problem but I still had the unreliability of both guns to deal with. I had tried about eight different types of 22LR ammo, both match and standard, without any observable difference. A little investigation was indicated.

Stripping the Ruger, Bersa,and Olympia I tried dropping various 22 rounds into the chambers. All brands dropped fully into the chambers without hesitation. Then I tried the Ciener and the Walther. For these, rounds dropped into the chambers stopped anywhere between 0.190″ and 0.040″ shy of battery. This was starting to make sense. The failures to fire, apparently in battery, were rounds that stopped just shy of the chamber. The first firing pin strike pushed them against the chamber lip allowing the slide to go forward fully into battery. The subsequent recocked attempt fired the round. Undersize chambers would explain all the failure events. Time for more gauges … results below.

The Ruger, Bersa, and Olympia all had SAAMI sporting chambers. The chamber labeled MATCH below is for match RIFLE chambers. As shown below that, the Walther chamber is smaller than the rifle match chamber and the Ciener chamber is similarly sized. Both are well under the sporting chamber standard size.

There is a recognized chamber for match autoloading pistols called the BENTZ. This is slightly larger than the rifle match standard chamber. Both the Ciener and Walther are distinctly tighter than this match pistol standard.

Others, Honest Outlaw for instance, have reported feeding problems with Walther 22’s … one suspects this is related.

The obvious solution is to give both to a gunsmith to have the chambers reamed out to the sporting dimensions but as I have an accurate small lathe and this is, after all, a hobby I decided to do it myself. Both the Ciener and Walther barrels are removable which eased the lathe set-up. I obtained a Manson Precision .22 LONG RIFLE FINISHER sporting chamber reamer from Brownells. It is necessary to finesse the Ciener ejector. (If this is not obvious then -> gunsmith) I indicated in the four jaw and the tailstock with a Jacobs taper chuck to hold the reamer concentric to <0.0005″. The main points here are to use a very slow speed, cutting oil, be very careful of the Ciener ejector as you feed the reamer, and most important, do not allow the shoulder of the reamer to contact the feed ramp on the barrel as you get close to bottom. If you nick the feed ramp you will probably ruin the barrel. You will NOT be able to run the reamer all the way in. This is not necessary as the cut described is completely sufficient to fix the feeding and reliability problems with the Ciener and Walther. As I finally found a 22 revolver, I now have six choices in my 22 rotation. 🙂

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Martian Off-equator Space Elevator

A decades old science fiction theme (or dream) has been the space elevator. This is a (really strong) cable running from the equator through geosynchronous orbit and then on to a suitable stabilization mass. Vehicles running up and down the cable would provide an efficient, low cost, route to planetary orbit and beyond. The technical challenges are immense requiring materials far beyond current state of the art but perhaps possible.

Building such an elevator on Mars presents two additional problems, Phobos and Deimos, the Martian moons which are directly in the path of an equatorial space elevator, unlike Earth’s moon. The blocks below indicate the extremes of the moons’ orbits. One suggested scheme is to create an elevator that sways back and forth under power to miss each moon as it transits, every 11 hours for Phobos and every 131 hours for Deimos. This is recipe for disaster, constantly dodging near misses and hoping nothing goes wrong or wears out in the maneuvering system. Initially it seems reasonable to locate the ground end off the equator far enough that the cable is above the maximum latitudes of the moons with a large enough counterweight to stabilize the revolution. Unfortunately, while stable, there is no way to actually build it. The traditional equatorial based design is built out from geostationary orbit keeping the up and down masses equal until reaching the ground. This is impossible here. With the elevator plane of revolution over the 45th parallel for instance as there is no stable orbit to build from.

However, it may be possible to build it out from one of the poles.

The main idea is like swinging a weight on a rope around your head and then letting out more rope. As long as you spin the rope fast enough the weight does not fall to the ground. While this is a serious mega-engineering project, just making the cable is probably the hardest part. Start with a large, massive structure at the rotational pole. Think the great pyramid at Giza but much bigger. Vertically through the middle is a hollow shaft topped by an eccentric crank with a bearing that connects to the ground end of the cable. The hollow shaft is driven to spin the cable. A streamlined mass is attached to the end of the cable. At initial launch, the eccentric and short cable assembly are spinning fast enough to keep the mass off the ground. The space elevator is is built out from the center through the hollow of the shaft which would probably of kilometer order dimensions. As mass is added to lengthen the cable and increase the counterweight, angular momentum would slow the rotation but increased centrifugal force due to increasing radius would keep tension on the cable. At first the angular drive from the shaft would need to contend with the atmosphere, hence the streamlining, where the drive has greater leverage. This problem will be reduced once the bulk of the mass is outside the atmosphere. With care it should be possible to balance the slow down with the radius increase to bring the end of the cable to a stationary condition at design altitude. At this time the cable will be moving synchronously with the planet which will eliminate drag and the eccentric will be aligned with the cable and no longer turning. By moving the eccentric ahead or behind by turning the shaft slightly, small adjustments to the elevator’s revolution speed or longitude can be effected as the planet’s rotation pulls or eases on the cable.

The figure illustrates the geometry for a 40,000km cable. This assumes negligible cable mass compared to the counter weight. Note the escape velocity locus. Any vehicle launched from the cable beyond this altitude will leave the Martian system without other effort. The plane of revolution is the 61st parallel. For this cable length the cable tension at the counter weight is 7.5 times the force of gravity. This makes the system fairly stiff against outside influences. For a 35,000km cable cable tension is 5.6 times gravity and the end is over the 53rd parallel. For a 30,000km cable the cable tension is 3.2 times gravity and the end is over the 43rd parallel. Shorter cables are cheaper but less stable in the presence of outside influences such as gravity from the moons and varying freight and vehicle transportation loadings. The closer the end gets to the equator, the less stable it is.

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A windage myth

A common misconception about windage is that the wind speed at the target is the most important. Superficially this seems reasonable since the slower a bullet travels the more it is deflected by the wind. An M855 is deflected by a 10MPH wind by 3.6 inches between 0 and 200 yards, by an additional 4.6 inches between 200 and 400 yards, and by an additional 6.4 inches between 400 and 600 yards which adds up to 14.6 inches but the actual 600 yard deflection is 39.3 inches as shown below. Something else is going on.

The point is that unlike a sailboat with an autopilot, a bullet doesn’t know where the target is. The wind blows it off course and so it is traveling sideways. After the first 200 yards it is traveling in the direction of the green tangent above. If there were no wind between 200 and 600 yards it would continue in a straight line with a total deflection of about 18 inches. The wind for the first 200 yards is responsible for 47% of the deflection. Similarly the wind between 200 and 400 yards is responsible for another 37% and the final 200 yards of wind at the target end is responsible for only 16% of the total windage deflection.

Pay more attention to the wind speed and direction at the shooting end for better results.

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Low Latency Contact Debounce Circuit

Electrical switching contacts are not nearly as simple as they seem.  Both at make (on) and break (off) they produce various undesirable side effects.  Transition times in the nanosecond range can produce unexpected reflections, surges, and arcs in long lines.  As the contacts make and break they bounce microscopically causing rapid on and off pulses lasting up to tens of milliseconds.  Sliding of the deflecting contact surfaces causes fritting that generates even faster pulses in the microsecond range. At circuit potentials higher than a few volts the bounces produce arcs whose effects range from electromagnetic interference to ignition of explosive atmospheres. This applies to light switches, electromechanical relays, electromechanical timers, and indeed any contact between solid conductors at different potentials.

In our modern solid state low voltage world, contact bounce causes problems with switch interfaces to computers and data gathering systems.  If you try to count switch events with an electronic counter it will indicate tens or hundreds of counts for each actuation.  A typical computer can read the state of a switch hundreds or thousands of times during the contact bounce time resulting in multiple “clicks” as far as the computer is concerned.  The normal solution to this problem is some sort of “debounce” circuit that filters out short transitions and eventually settles to the desired state after 50 milliseconds or so.  This works well for mouse buttons or remote TV controls.

Unfortunately this is undesirable for instrumentation, test, or metrology applications, especially multi-channel applications.  The delay time will vary from channel to channel and will be affected by the bounce duty cycle.  This will make it impossible to accurately determine the time of the initial event closer than a few tens of milliseconds.  As an example, in industrial testing it is common to test cam switches at higher than normal speed and correlate the event timing with the cam dwell times which requires very accurate measurements of the initial event timing and sequences.

This circuit essentially solves the contact event measurement problem.  The switch signal passes through a spike filter and then through a transparent latch.  The output of this latch is the cleaned-up input signal and is applied to an exclusive-or gate with a delay on one input.  When a transition passes through the latch, the two inputs of the gate are briefly different.  This causes the output of the gate to pulse low, holding the state of the latch for the duration of the delayed channel of the exclusive-or gate.  This delay is selected to exceed the length of any expected contact bounce but to be shorter than any expected valid signal repetition.  At the end of this time the exclusive-or gate unlatches the transparent latch and it reverts to normal.  Note that since the contact will have completed its event the output of the latch does not change.  As the exclusive-or is not polarity sensitive, this circuit works the same way for rising or falling edges.  One consideration is that the data input to must hold steady until the exclusive-or signal is able to latch it.  This is about two propagation times or a few nanoseconds for typical logic families and is the purpose of the input spike filter.  Its input time constant should be just long enough to guarantee this condition.

This circuit enables contact event measurements with time resolutions of a few nanoseconds.

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Locking Loop Knot

A particularly good knot for tying down tarpaulins is the slipped locking loop.  This is an adjustable self-locking loop knot that is easily untied, even when frozen in winter.  It is described on page 137 of John Shaw’s Directory of Knots.

Tie a stopper knot (either  Ashley’s or a quad stopper) in one end of a rope and pass it through a tarp grommet.  Take the other end through or around the tie down point forming a loop.  Pull on the working end to make the rope taught.  Form the main loop and slip loop, as shown above, near the tie down point.  Snug up the knot enough that it will just barely slide on the standing end.   While pulling on the working end to tighten the rope to the tarp, slide the knot away from the tie down until it snugs hard against the working end.  The main loop will pull the standing end around the slip loop and lock the knot in place.  Load tension from the tarp end will lock it tighter.

To remove the tie simply pull out the  slip loop and the knot will fall apart.  This feature is very useful for applications like covering car windows in the winter where freezing rain and snow-melt-freezes will completely lock up ordinary knots making them impossible to untie.

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