pat

As a further aside to this I was contemplating the interesting effects that we see during load development. We can tune the load in three main ways - powder type/charge weight, seating depth and barrel tuners. With further thought it would make sense to include things like neck tension. One thing I found interesting is the appearance of velocity nodes. Whilst working up a load, we can get to a point where the increase in MV begins to level off a bit, before it starts climbing again. This didn't make a huge amount of sense. But it did make me wonder if there could be a similar phenomenon at play here. It is generally the case that giving a bullet more jump before encountering the lands causes a reduction in pressure and speed (QL will indicate the opposite, but that is another story). This happens, I believe, for a few reasons : 1) a bullet seated deeper leaves less "free space", ergo less gas needs to be produced to overcome the neck tension so the mass fraction alight at the point it starts moving is lower, 2) because there is less "free space" to start with, then for the same forward movement the volume increase ratio will be higher thus moderating the pressure more and 3) a bullet which is already moving will engrave / obturate more easily (static friction is normally higher than dynamic friction - this also explains why you need to be careful when seating into the lands - QL recommends increasing the Shot Initiation pressure substantially and for good reason). Taking that into consideration, and not messing with the jump, but only the charge weight, it should become apparent that something similar can happen. If we add more powder, then this reduces the "free space", which in turn reduces the mass fraction that must be alight in order to start the bullet on its way, which will then moderate the gain from the additional powder. But of course that should "always" be the case whenever you add more powder. And perhaps to some extent it does happen - it would be interesting to try using an inert filler material in lieu of actual powder to see what would happen if the mitigation of the reduced volume was eliminated - I digress. I'm not entirely sure "what gives" with regard to why this effect is more pronounced at some loads than others. It is possible that some sort of hoop-stress shear wave (c.f. Chris Long / OBT) is interacting with the bullet, or it could just be down the the mechanics of the engraving / obturation (perhaps there is a partial "stall" going on which is widening the pressure / speed plateau). It is interesting to note that the above mechanism which is responsible for the reduction in pressure / MV as we shorten the round must also affect the barrel time, and hence it should come as no surprise that it is possible to tune the load that way. Moreover it is likely possible to tune different aspects of the load - that is to say that there are some barrel motions which are "slow" relative to the exit-time-variance, and so we may observe a drift in POI as the charge is changed (as well as a possible group size reduction), whereas within reason we may be less likely to observe a general POI shift as seating depth is changed. In terms of group size, I found it quite interesting that a small change, say 5 thou, in seating depth can make or break things - but with the extra mechanisms at play that is much more "understandable" than what happens with barrel tuners. Here again, we can see a substantial difference in group size with just a small change in location. Many tuners have rather fine pitch threads and a whole revolution may be only 40 thou, and yet we can see enormous differences within 1/4 turn, which would again only be 10 thou! As I see it there are two (not necessarily mutually exclusive) possibilities for why any given bullet's POI is not exactly where the crosshairs were (assuming a correct zero, of course) : 1) the barrel wasn't pointing in the right place or 2) the bullet got nudged off course. By 1) I am referring to barrel motion ("harmonics") - if we have a small variance in exit time and the barrel is in a "rapid" part of the harmonic motion, then it should stand to reason we should see some stringing, in the direction that the barrel is moving at the point the bullet exits. By 2) I am referring to one of two mechanisms - a) Chris Long's idea that a hoop - stress shear wave is at the muzzle at the point of exit, which has enlarged it to the point that the bullet is no longer in contact with the entire circumference of the bore - then given the variance in centre-of-mass from bullet to bullet, the bullet will exit when it is touching some "random" part of the bore, and hence we see random scatter, and b) acceleration of the muzzle in a direction normal to the bullet path causing some "tip off" - that is to say imagine the barrel moving sideways (say it's on a train, pointing out a window sideways), but the bullet is also going sideways, both are going sideways at the same speed and so there is no relative motion between them, ergo the exit will be "clean", but what if the train applies is brakes ? well, whilst the bullet is still in the barrel, it will slow the sideways motion of the bullet, but that is only possible because the bearing surface is in contact with the bore - but what happens as the leave the muzzle ? when the bearing surface is half way out - 75% of the way out - 95% of the way out ? The barrel will still be slowing down, but it is only touching the bullet behind its centre of mass, and so it would try to "tip" the bullet. Delete the train from the picture and replace it with barrel harmonics. If the bullet exits at a time that the barrel is accelerating in any direction normal to the bullet flight, you may end up with "tip off". We know that aerodynamic jump causes deflection in "unexpected" directions, due to the angle between the axis of rotation, the flight trajectory and the ambient wind, so it stands to reason that any deviance, however caused, may have an influence. If the group size was purely down to the harmonics themselves causing the bbl to point in a different direction then two things "should" be true : 1) we should see some sort of Lissajous pattern emerge in the impact locations (but they appear random) and 2) it would have to be a very high order harmonic - given a total barrel time of 1.35ms (will vary, just a suitable example) and given that a substantial change in bbl time would be quite noticeable in its effects on MV (delayed ignition aside, ahem, err), we should not really be seeing exit-time variances much longer than 0.025ms....which would be 20kHz if we're thinking peak-to-trough - and so far no one has suggested / simulated harmonics that high (think Varmint Al went up to 1.5kHz is). That's not to say this isn't possible.... indeed perhaps there is some ultrasonic excitation from the primer detonation..... worthy of further thought My gut feeling is that sizes are down to a mechanism proximate to harmonics but not necessarily directly related. Changing the "length" of a barrel from 26000 thou to 26005 thou is not going to change its resonant frequency by much - it's a 0.019% change - equivalent to putting 50.0096gn into a case when you "should" be putting in 50.0000gn. Whatever the tuner is affecting, it's much more sensitive than that! I am minded to think about wave theory again - the very notion that "the speed of light is too slow" is fascinating... that you can apply and measure several thousand volts to a "dead short" just because the "dead short" is finite in length and it takes time for that voltage to appear at the other end of the "dead short" "wire" means that for a (admittedly rather brief) period of time, this situation is "fine". Indeed if one times it well, so that when the reflection comes back from our short (the opposite voltage is reflected to cancel out the original) we are outputting the opposite as well, then it actually looks like an open circuit - pretty crazy, and all because the speed of light is so slow That being said, the same should be true in steel as well. A shear (transverse) wave applied to one end will travel to the other, and when it gets there it will reflect, but it could wiggle things about "vigorously" whilst there. Trouble is that the wavelength in steel will be somewhat longer.... 20kHz would be around 16.25cm. And we're talking about moving something a few thou. Mmmmm Cheers, Pat.

Evening all, whilst discussing load development I happened to mention that I would always target a bare minimum of 85% fill ratio, with the rationale that anything lighter can be dangerous. I hadn't previous given it much thought as to why that should be the case, and when asked to justify this, I had to say "let me get back to you on that one". I hadn't needed to understand it at the time, and so didn't have an answer on hand, but I have had a chance to think about the internal dynamics and I think I have been able to tie a few things together that form an overall coherent theory that may explain some interesting phenomena - including why a light load can be an issue. Thinking about a loaded round, we can make some observations.... the case has a given volume, which is reduced by the seating of a bullet.... powder kernels are solid (be they ball or extruded).... powder has a bulk density which is different from the kernel density (there is some air in between the balls / or kernels). These should all be axiomatic and require no further proof. Thinking about the way that smokeless powder burns, there are a number of salient points.... powder turns from a solid into a high temperature gas... the rate at which this happens is affected by the pressure in the case.... the rate at which this happens is affected by how much of the powder is already burning (current mass fraction). The second and third are ostensibly conjugate - the more hot gas there is to set other kernels alight, and the higher the pressure the more those gas molecules are likely to bump into an unlit part of a kernel the faster it lights, whilst the higher the percentage of the powder that is already alight, the faster it will release gas, and so it goes on. It is noteworthy that as the kernels burn, they "create volume" that gas can occupy. At the initiation, a large percentage of the available case volume is occupied by solid powder and so is not available for gas to expand/compress into. Now that we understand some of the mechanics of what is going on we can think about what must happen in order for things to work the way they are supposed to. Given the powder's desire to exponentially burn and build pressure, if it was fully contained then we'd end up with an actual explosion eventually (that is how a bombs work, though it is notable that the term "bomb" initially refers to a confined space). The fact that the bullet is "not" confined (it is "free" to move) is what allows the pressure to stabilise - as the bullet moves forward, it is adding more volume which the gas can occupy - applying Boyles' Law or the Ideal Gas Law shows us that increasing the volume decreases the pressure (which, in turn moderates the burn rate). Most smokeless powders use a base which has pretty much the same burn rate, and so the difference between a "fast" powder like Bullseye and a "slow" powder like H50BMG comes from the use of retardants and the surface area:volume ratio - but fundamentally the powder, if in the same shape and not coated, would all burn at the same speed. Fortunately we do have retardant coatings and different shapes to control the burn rate. Now, an interesting point was made - "if X amount of powder only generates Y pressure, how can 0.5X make more than Y pressure?" - now I was a bit slow on my feet at the time and a sensible retort might have been "well, try putting 120gn of Bullseye in a 50BMG, stand well back, and let me know what happened!" Given that you can get 240gn of an appropriate powder in there safely, I think this demonstrates the point that it is not just the amount of the powder that is important. Hold that thought! In order to push the bullet out of the case, we need to overcome that static friction between the neck and the bullet - we need to reach a certain amount of pressure. The amount of powder that needs to be burnt in order to achieve that pressure depends on the free space in the case to start with. Remember that powder is not a monolithic solid that fills the case, it is a collection of balls or kernels with air spaces between them. The amount of space available for gas to expand / be compressed into is a function of how much powder is in there to start with (kernels are solid and "can't" be compressed like a gas, so any space they occupy at the beginning "does not exist" for gas to occupy). If the case it very full then there will be only a small amount of "free space" - therefore it doesn't take much powder to burn before the required pressure is reached to unseat the bullet. But now let's imagine we get rid of half the powder. Rather than"doubling" the free space in the case, we may have increased it by a factor of 20 or so! It stands to reason that much more powder has to burn, in order to generate the same pressure - it is after all filling a much bigger space! Now, the burn rate of the powder depends on the mass fraction that is already alight. And now the problem reveals itself. Far too much of the powder is already alight, and evolving gas at a rate far too high, for the nascent motion of the bullet to effectively relieve. If we think about the original scenario where the case was full, there was only a small amount of "free space", so any small motion of the bullet would enlarge that space significantly, but when there is already a large volume, then a small movement of the bullet will only have a tiny impact on the pressure relief, and hey presto, things have gone rather wrong. In order to not end up with a ridiculously enormous single post, I'll make some further observations in other posts Cheers, Pat.

Hiya Matt! Apologies for the delay in replying. The topology tool is a very useful one I'll try to get a 0.5m and a 3m cable made for you. I have a number of connectors so that will be fine. And of course if anyone else wants, then I can do that too. The silicone cable that I used was one I sourced from Amazon of all places. I didn't want to buy a 100m roll of it, just needed enough for 2 or 3 cables. I can try to find the listing again it that would help. Cheers, Pat.

Matt, Price for flying leads are likely in the region of UKP 15 - UKP 20 ish. Not sure what you define as long or short - gonna imagine something like 3m and 50cm but you may have something different in mind. I don't have any of the flexible silicone type cable in 5 core so would make it using Type 55 Raychem twisted with an outer heatshrink sleeve if that suits ? I'm sure you can come up with a way of persuading the binos to stay put in that tripod - worst case you may be able to do something like the universal Swaro mount which is a support frame the binos sit in with some straps up top to hold it securely in place. There are likely more elegant solutions as well Regarding astronomy, yes, I also do a bit of astrophotography - and yes, 0.3 arcseconds is indeed to prevent, to the extent possible, trails / elongation. I typically operate at around 0.6 arcseconds per pixel and I prefer my stars to be round. When all is going well the guidescope seems to be able to keep the errors down to sub-half-arcsecond. To be fair even at 1 arcsecond, it wouldn't be a a disaster, but why settle for that when better is possible In order to see further than 19km you'de need to have a clear elevation of at least 30m higher than anything between you and the observed object. Oddly enough I have some experience of clear line of sight stuff as well, LOL. You can explore topography pretty well using resources such as heywhatsthat.com..... when you can't rely on tropospheric ducting or sporadic-E you have little choice but to get a better vantage point I digress.... 73 es 30 de Pat.

Afternoon All! As promised, thread updated to reflect the fact that more connectors have now arrived Cheers, Pat.

Hiya Mart, Yes, the binos are still available Cheers, Pat.

Matt, A good support can make a HUGE difference, though when it has to be ULTRA stable (whilst still being portable) then I find that a Tri-pier is about as solid as you can sensibly get - beyond that you're actually anchoring things into the ground. When you need to track 15.041 arcseconds per second and any error exceeding 0.3 arcseconds causing issues, you being to appreciate solid support Beam divergence is a real PITA. You can of course trade beam diameter against beam divergence but I'm not sure that helps (need to run the numbers to be sure). Target albedo will have a considerable impact on ranging capability - though of course you can mitigate that with higher pulse energies - with (say) Nd:YAG lasers you can get a 10J pulse lasting 1 nanosecond - would be fascinating to see what Vantablack or similar coatings would do with a 10GW pulse (maybe just ablate - a bit brutal but you might get a ping off it, LOL). Regards the AS connectors, I've been known to hang around some interesting vehicles, yes, but few will spend on things like AS and DR25. I'll certainly update the thread when the balance of connectors arrive - and I can indeed sort out a "flying lead" or two for you Cheers, Pat.

Matt, The right angle version is indeed tidier but it is also a lot more expensive from Lemo. Sure, if you need it to be that way the fair enough (and I doubt that Safran Vectronix were too concerned about the cost of the connector given the intended market). Those crimps look very familiar - I have a set in blue with a positioner for AS pins And a larger set with adjustable positioner for the DT / DTM pins.... it is a PITA when you find that you have the wrong positioner though Cable seems to be doing a decent job - it is now "trivial" to range telegraph poles against the sky at around 1000yds without missing and "ranging" thin air - a good fluid head on a tripod works wonders for that. Really easy to hold rock steady on the thing you're trying to range as no force needs to be applied to the unit Ranging daisies at 500yds is also trivial - but one does need to bear in mind the beam divergence is somewhat wider than the reticle subtension at the aim point! Cheers, Pat.

I have a "spare" set of the original 10x42 EL Range if they're any good to you

Matt, The Deutsch DT(M) series are nice insofar as they use good pins, but then a cheaper plastic housing - so if you don't need the ruggedness of the AS type but still want the high quality contacts then they could be a good compromise. Lemo crimp wise, I would suggest that FGB-0B-305-CYCD42 would be a suitable crimp version of the mating connector for the PLRF. The "usual" solder version is the CLAD version, but if I am reading the catalogue right then CYCD would be a crimp version of the same connector. You will likely need a nice crimp tool though. When I'm not shaking like a dog relieving itself, I can happily solder 0.5mm pitch devices, so I just went with the solder variant. Cheers, Pat.

Matt, The etched reticle means it is possible to accurately position the RF before you press any buttons - having to have the electronic reticle on can be a pain since then most rangefinders will want to take a measurement. The PLRFs I believe will hold off the ranging until you let go of the button, so you can light up the electronic reticle (when darker) and align, but it always struck me as interesting that not more manufacturers etch reticles on rangefinders. I suspect there will be commands that can be sent to the unit to tell it to switch modes etc - just haven't seen any docs for those (yet). Though you could of course use something like an Arduino to automate "pressing" the buttons. And yes, you could certainly use the output from the RS232 for some useful purpose. That thought had crossed my mind - maybe a cheaper Serial <> Bluetooth interface to then connect to an App, say. Trouble is that Apple locked down their BT and you need their auth chips to talk to them! Should be fine on Android though Re-reading your post, the idea of a remote display (as connected directly over RS232) is a pretty cool idea - that way you could collimate a PLRF with a spotter with reticle, and you would not need to aim with the spotter then swap to the PLRF for the answer, just taking your eye off the spotter would allow you to see the display. Mmmmm There are indeed Lemo copies out there, but Lemo UK were most helpful and the pricing was sensible enough that there was no good reason to risk an inferior product. I went with the straight rather than the right angled body - for the intended purpose it should be fine and they are a lot less than the (admittedly nicer) right angled ones. Lemo are already better priced than the Deutsch connectors (though I do like the AS series). Cheers, Pat.

Hiya Matt! Good find on the pinouts - and I suspect that the reason it differs to mine is that I may have started counting at a different place - I called the pin in line with the index / datum pin number 1 and counted clockwise from there, but if we go counterclockwise then what I called pin 5 would be pin 2, etc - in which case it all lines up Of the sets you have I personally would find the Rockwell set more useful based on the engraved reticle - that's one thing that the PLRFs have that is most useful compared to others that have an electronic reticle. I had a reasonable idea regarding the serial data format - the distance was too long so I figured there was a checksum at the end, and the other 2 fields were placeholders (mine don't have the compass) which I figured would be filled on units that did have the requisite hardware. I didn't specifically want to do anything with that - I was just seeing what each pin does when the range button is pressed The keying is a pain - Vectronix used a less common keying - had they used the usual "G" keying rather than the "B" keying, there likely would have been more in stock. Hey ho. I was reluctant to use a key-less plug, just in case it got inserted the wrong way by accident - something that is avoidable by using the right keying Cheers, Pat.

Hiya Matt! I was somewhat frustrated that it wasn't possible to buy just a trigger cable on its own, without the serial or USB, which I didn't need. Seemed sensible to just make one And I'm not at all jealous that you have two Vector binos! You are correct in the assumption that the remote trigger pulls the relevant pin to ground. I originally was testing with 1k for safety, but since there appears to be in the region of 82k pullup it seemed quite safe to just ground it. That certainly works for the cables I have made thus far. Interesting that your manual enumerates the pins - that was not the case for the PLRF manual(s). I had to work it out by measurement. Would be interesting to see if your manual concurs with what I found.... Pin 1 is the "function" button, Pin 2 is RS232 Transmit, Pin 3 is RS232 Receive, Pin 4 is Ground, Pin 5 is the "range" button. I can certainly make a cable that is un-terminated at the other end, though I would need to know which pins you would be interested in - these cables (bar my first prototype which has 3) have 2 cores, one for the range button and one for ground. This is a highly flexible silicone cable - but I can do a twisted triple, quadruple or quintuple if you need access to more of the pins. Please be aware that I am currently awaiting delivery of more of the connectors (Lemo UK only had 3 in stock at the time), they are predicting that they should be with me in June. Cheers, Pat.

As a heads up / courtesy, the two connectors I have here are now spoken for. More are on the way, so it is still possible to get one, but they will be available in June (unless the connector manufacturer delivers sooner than promised, of course!). Cheers, Pat.

Rangefinder has some use but has picked up more cosmetic blemishes than normal for one of my pieces of optical equipment. Rangefinder returns distances very close to those from a Vectronix and is suitable for intermediate distance use (no issues in bright sunlight to 700-800yds, but may struggle in sub-optimal conditions beyond that distance - though in cloudier conditions it will work much further). Optically "perfect" - by which I mean as new - but don't expect Zeiss or Swaro levels! Also available with this is a Really Right Stuff tripod adapter. I'll list those separately since they are useful on other SIG rangefinders. Price wise I really have no idea what to ask for this. OPW were asking UKP 520 for these new and the KILO 2200 is now UKP 599, so I'll give the ball a kick at UKP 300 and see how far it rolls. As always, I'm open to negotiation Feel free to PM me if interested but want a private chat. Cheers, Pat.