The MX991\U is a design that has been used by the military since 1940, is still in use AFAIK. It's light weight, rugged and waterproof.
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They're cheap on EBay, often under $10. One recently went for $3.30.
I modified mine to accept the Maglight 3-watt LED "bulb" that sells at Wal-Mart for $18. The modification took less than 2 hours, not counting the trip to Wal-Mart.
It isn't as impressive with the LED as the 2D Maglight with the LED was, but it's far better than with the stock incandescant bulb and it's a lot lighter weight and easier to carry than a 2D Maglight. The Maglight does have a bigger and better reflector so it produces a better brighter beam with the same light source.
I figure battery life will be about 20 hours of full-brightness operation. Survivalists might like this because it's military-rugged, easy to carry, delivers constant full brightness for nearly the entire life of readily-available cheap batteries (D-cells), and at about $25 for both flashlight and LED module it's a hell of a lot cheaper than a lot of LED lights that aren't nearly as good.
Geez, I'd forgotten about that, Gunner. I think one is enough for me at the moment, thanks. However, if you want to mod one of yours I'd be glad to make a bulb retainer for you. I know you could do it on one of your several lathes, but I probably have more time than you do. If you send me the positive contact I'll also stick a bump on it, and then nickelplate both parts. I turned the contact bump on my lathe. It's .090 dia with a .062 post that I stick in a hole and solder in place. I can't buy parts and build the LED and elex for what Wal-Mart now sells the Maglight 3Watt LED with pretty good elex. I'll say again that the 2D Maglight with LED is more impressive if ya don't mind the weight -- and put some Penetrox on the tailcap threads so it doesn't gall.
Another project in the wings: another correspondent has gotten into long-range shooting, wants to study the strain behavior at the muzzle of his rifle. There is some opinion that dispersion (group size) of a given rifle depends a lot on when the bullet leaves.
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We don't entirely believe this simulation and would like to see actual data on a scope to directly observe OBT (optimum barrel time) on his particular rifle. The thesis is that each rifle will have a time window of OBT, time between pulses. Once that is known, one can then tune loads to be within that window. So he plans to stick some straingages on his rifle, my part is to cook a couple of postage-stamp-sized straingage preamps with risetime of under 2 microseconds. Don't want long leads on straingages if looking for 200 KHz bandwidth.
What's that Lassie? You say that Don Foreman fell down the old rec.crafts.metalworking mine and will die if we don't mount a rescue by Sat, 23 Sep 2006 00:03:12 -0500:
Take a look here:
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I he uses a lense make for LEDs so his may be better than using the Maglight conversion 'bulb'.
Have you looked at piezo-sensors? They're often better suited to observing high speed transients than strain gages, and avoid the problems dealing with millivolt signals. The frequency response of strain gage based transducers (load cells, pressure transducers, etc) is quite low (10s of Hz?), primarily due to mechanical resonance - this may not be a problem if you're bonding the gages directly to the barrel.
The Maglight elex do a pretty good job of driving a 3W Luxeon from two C or D alkaline cells. Better reflectors always work better; reflector efficiency can make more difference than more lumens. The reflector in the MX991/U is not great, but using it is very easy. The one from Elektrolumens is only 27mm. Larger dia is better as long as it's a deep short-focus reflector. A better choice might be a Carly 1.5" dia short-focus reflector, which would fit in the MX991/U. That would require a bit more machining and re-work but not a big deal.
Piezo senses force. We want to measure strain or deformation. The straingages will be bonded directly to the barrel. I should check with Omega about intrinsic frequency response of foil straingages, but I see nothing that would prevent one from working up to frequencies where the straingage size would become a half-wavelength of sound in the material it's bonded to. They have very little mass and their resistance is low enough to make their capacitance and inductance negligable even at 1 MHz and above.
Yall are reinventing the wheel. Google "Browning BOSS System"
Its designed to minimize muzzle harmonics, and does a rather fabulous job of it too. That barrel harmonic is created by bullet time in the barrel, and while there are shot to shot variations of upwards of
100-200 fps with factory ammo, if you calculate the time in the barrel (discounting accell time..total barrel time is what counts)..you will note that at say...2700 fps muzzle velocity...barrel time is mighty short..but that variation of 100-200 fps is a pretty small percentage.
It ALWAYS makes a difference where the bore line is when the bullet leaves the barrel. Light barrels have more harmonics then do heavier tubes..or dampen better..hence on average, fat barrels are more consistant than skinny ones. The Boss System balances out the harmonics...or dampens them as it were. A free floating barrel, glass or pillar bedded action..and the only thing of significance and vibrating thing IS the barrel. Truing the locking lugs, truing the barrel/receiver join simply makes secondary harmonics less likely...or less significant.
Yes..it does make a difference When the bullet leaves..as the harmonic cycle may have the bore pointing in slightly different directions if you are leading or behind a common point in the vibration. Think of it as a sine wave. Zero/Zero is bore dead nuts. A rise or fall in the sine wave will put the bullet exiting in a slightly different direction. Now extend this to a circle..barrels may be pointing at any degree in a circle when the bullet exits..the idea is to consistantly exit at that same point every time. Say...240 degrees. If the bullet exits early..it may exit at 134degrees, or late..320 degrees. Barrel harmonics tend to whip the end of the barrel in a circle, both because of the rifling having a great deal of effect on progression. (right and left twist, twist per foot etc) etc.
Ultra highspeed photography shows a number of stress events on a barrel while the bullet is traveling down the tube. Torque in the opposite direction of the twist. The Snake Swollowed the Rat expansion as the bullet passes down the tube, an elongation which gets greater as the bullet gets closer to the muzzle and so forth. Rather fascinating.
Then too, external forces such as temperature of the barrel steel makes it slightly "stiffer", fouling, which acts like accoustic material providing some dampining, and additional friction and so forth. Which is why fouling shots are fired before going for score..and so forth.
Toss in some variable stress forces within the metal itself (hence cryogenic treating to make the barrel more homogenious) and so forth.
Thats not even including the variables of the ammunition and its components, lock time etc etc
But it sounds like an interesting project. Let me know the results.
Respects and regards
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences."
On Sat, 23 Sep 2006 23:12:40 -0500, with neither quill nor qualm, Don Foreman quickly quoth:
Right. On my latest jaunt to Medford, I hit the HF (big surprise) and picked up a few of the waterproof Gordon headlamps. They're standard bulb and dual AA battery, but they were on sale for $1.99, including batts. I picked up 5 and popped them in drawers around the house + 1 in the truck. These put out about triple the light my Remington 3-led headlamp (2 AAA) is capable of, but the meek Remington also has red leds which allows retention of night vision. Each one has its place.
I picked up some white leds last year and mated them to 9v batts with current limiting resistors. They'll be OK during longer blackouts.
I want to build a good, bright, super-long-lasting led flashlight and have been waiting for the Luxeons to drop in price. I love new technology but seldom fund the first year of it. (I'm way too cheap for that. ;)
I, too, would like to hear about the rifle strain testing project you're working on, so do keep us informed, please.
-- Jewish Zen: Be here now. Be someplace else later. Is that so complicated, already?
Hmm. I've been thinking about this for a while, this will probably cause me to get off my (cheap) butt about it. I've got an old 6V lantern (BIG reflector) which might make a good candidate for reworking. I can rewire it to 2 D cells (leaving room for storing a few other things inside it,) or do a smoke test to see if the electronics supplied are smart enough to relax and enjoy extra voltage. But part of the appeal to reworking it is that 6V lantern batteries are an oddity these days.
I made a Luxeon light from the 6 volt lantern from Home Depot. I chopped the plastic case and shortened it so I could use AA cells. This yellow and black"stubby" lantern is 3 1/2 inches long and 3 3/4 inches diameter. Don Foreman made me a mount for the Luxeon that allows the LED to be positioned in the reflector so it can be focused easily. The Stubby is much brighter than the original 6 volt lantern.
I think I know where you're coming from, but both piezoelectric materials and foil strain gages respond to induced strain.
Okay, that makes sense. The problems arise when, in order to get a reasonble output level from a transducer, the gage must be mounted to a relatively flexible member.
Piezoelectric is probably cheaper than foil strain gages, or do you mean piezoresistive? Foil strain gages are certainly more accurate. If you want actual measurements rather than relative levels of tension and compression, piezoelectric may indeed not be practical.
How many points do you think you need to monitor? If I understand the goal, I expect you need to look at several points, and 2 or 3 axes per point, in order to get a clear picture.
I think we're just interested in one point and one direction: diametral expansion of the barrel at the muzzle as fn of time. A second SG would be used near the breach just to trigger the scope or datalogger.
But the propagation velocity of sound (hence strain) in steel is much faster -- about 15,000 ft/sec. A floating barrel on a pillar-bedded or glass-bedded action is a mechanical analog of an unterminated transmission line -- although more complex because there are 4 degrees of freedom: X, Y, torsion and elongation. The disturbance that occurs when the cap pops will cause perturbations in the steel that propagate down the barrel, are reflected from the impedance discontinuity of the end, and so on.
The idea here is to avoid the most chaotic periods. A very few microseconds may mark the difference betwen when the barrel is pointing 240 vs 320 degrees during an active period -- but there is some evidence that there are periods of considerably more than a few microseconds when the muzzle is relatively still.
Yeah, if one has the budget for high speed photography! The thesis here is to find periods where the muzzle activity is relative low, and tune the load so the bullet leaves during a period when the muzzle is relatively quiet -- and do that with less investment than the ammo required to get it right by blind trial and error over thousands of rounds.
The hole in the paper downrange gives a pretty good indication. Our interest is more in reducing dispersion from round to round to minimize group size. We can always re-zero the scope.
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