Labradar Tolerance of Obstructions

[williada]

You don't need a chronograph. . Here's how to do it without one if you are desperate. https://www.youtube.com/watch?v=FZxizte6foI

Its what's on paper that counts if you remain well over transonic speeds at long range. Extreme spread velocities show up in the elevation.

Could be a head space issue with that high speed Chris? i.e. round bumped way back. Just joking, but there is an element of truth in that which relates to case volume and high pressure. One, not that high in project Penumbra with issued blue box used at Bisley which was a hundred feet faster and a definite outlier. Did not believe the velocity at first but thought otherwise when the other equipment confirmed higher temperature and higher pressure for the same shot out of the machine rest.

[pjifl]

Here are whole lot of odds and ends relating to this. BTW, I do not dispute that Chris's experience happened but I have never seen anything like that. We will never know why !

An error caused by sighting the LR at an angle to the trajectory would be predicted by considering goemetry.
1 degree aiming error could produce a 1 to 2 % error. This increases more or less linearly up to about 5 degrees.
This also applies to a MagnetoSpeed and old Optical or screen Chronograph as well.
Place the LR very close to the muzzle and take great care to reduce aiming error.

Misalignment of the LR will also reduce the signal strength of the echo as well as introducing a cosine error (as above).

I have shot through two inline Magnetospeeds. I had 3 to choose from and tried different combinations. The disagreement was quite high and WAS QUITE INCONSISTENT FOR EACH SHOT. One might expect one MS to be consistently higher or lower but this was masked a lot by erratic disagreements. When MSs came out, they helped me improve my shooting but I trust them less than LR. I have also shot through an older optical Chrono in line with MS. Again agreement was quite erratic within each shot.

Trying to determine velocity or ballistic coefficient by working back from fall of shot as in that video carries a huge error budget. It is about the worst possible method - especially to calculate ballistic coefficient. One has to make huge assumptions about the shooter, rifle, barrel, and atmosphere. Remember that Aerodynamic Jump will also influence bullet height as well and may even vary for each shot.
In any case it is like a dog chasing its tail and the errors become circular.
There are ways to measure bullet velocity - some almost entirely mechanical but very few people will want to perform the experiments. Shooting through two spaced spinning paper disks is one. Another is the ballistic pendulum.
A warning - never use conservation of energy, rather conservation of momentum when reducing data for the ballistic pendulum. But also never shoot very close up into the pendulum - splashback can be dangerous. I used to perform a lab experiment for classes way back in the 60s with an air rifle. It was a different world back then and this was a small rural school and everyone had firearms.

Unfortunately, there is an error budget even with these methods but at least there is no or almost no dependence on unknown calibration of some bought in instruments.

If you only want a rough measurement, all of these are useful. But as for fine accuracy we use to draw conclusions, that is just not so.

Peter Smith.

[Pommy Chris]

You don't need a chronograph. . Here's how to do it without one if you are desperate. https://www.youtube.com/watch?v=FZxizte6foI

Its what's on paper that counts if you remain well over transonic speeds at long range. Extreme spread velocities show up in the elevation.

Could be a head space issue with that high speed Chris? i.e. round bumped way back. Just joking, but there is an element of truth in that which relates to case volume and high pressure. One, not that high in project Penumbra with issued blue box used at Bisley which was a hundred feet faster and a definite outlier. Did not believe the velocity at first but thought otherwise when the other equipment confirmed higher temperature and higher pressure for the same shot out of the machine rest.

I know you were joking but the action would have been it bits, the shot joined the group so velocity was the same the Lad radar stuffed up.
Chris

[Pommy Chris]

Here are whole lot of odds and ends relating to this. BTW, I do not dispute that Chris's experience happened but I have never seen anything like that. We will never know why !

An error caused by sighting the LR at an angle to the trajectory would be predicted by considering goemetry.
1 degree aiming error could produce a 1 to 2 % error. This increases more or less linearly up to about 5 degrees.
This also applies to a MagnetoSpeed and old Optical or screen Chronograph as well.
Place the LR very close to the muzzle and take great care to reduce aiming error.

Misalignment of the LR will also reduce the signal strength of the echo as well as introducing a cosine error (as above).

I have shot through two inline Magnetospeeds. I had 3 to choose from and tried different combinations. The disagreement was quite high and WAS QUITE INCONSISTENT FOR EACH SHOT. One might expect one MS to be consistently higher or lower but this was masked a lot by erratic disagreements. When MSs came out, they helped me improve my shooting but I trust them less than LR. I have also shot through an older optical Chrono in line with MS. Again agreement was quite erratic within each shot.

Trying to determine velocity or ballistic coefficient by working back from fall of shot as in that video carries a huge error budget. It is about the worst possible method - especially to calculate ballistic coefficient. One has to make huge assumptions about the shooter, rifle, barrel, and atmosphere. Remember that Aerodynamic Jump will also influence bullet height as well and may even vary for each shot.
In any case it is like a dog chasing its tail and the errors become circular.
There are ways to measure bullet velocity - some almost entirely mechanical but very few people will want to perform the experiments. Shooting through two spaced spinning paper disks is one. Another is the ballistic pendulum.
A warning - never use conservation of energy, rather conservation of momentum when reducing data for the ballistic pendulum. But also never shoot very close up into the pendulum - splashback can be dangerous. I used to perform a lab experiment for classes way back in the 60s with an air rifle. It was a different world back then and this was a small rural school and everyone had firearms.

Unfortunately, there is an error budget even with these methods but at least there is no or almost no dependence on unknown calibration of some bought in instruments.

If you only want a rough measurement, all of these are useful. But as for fine accuracy we use to draw conclusions, that is just not so.

Peter Smith.

Hi Peter,
I have had a person very close to me at SSAA so I am uncomfortably close and their shots read 2000 or less fps as they are 2 feet away and real speed is 3000.
My question re the lab radar and more of a musing as I have already a theory is a few degrees makes much differences ans your odd 30fps anomaly could be just this. The pic above shows the lab is far from infallible.
Chris

[williada]

Yep Chris, I was having a bit of fun even with the video. I only use chrono's et al, as a rough guide. There maybe something in that 30 fps anomaly as you suggest as Peter has indicated with the echo strength and the cosine error. I make a point of getting the muzzle as close as possible to the LR at its mid point on the side of it. On balance I think you had a LR glitch. If it continued to give errant readings on an open range, I would want a replacement. I'm going to take up Barry's suggestion and look through the casing of a ball point pen because I think alignment is critical.

I do note that my LR was within a few fps of the Rosedale club's MS a couple of years ago shooting in the open. At another time, my readings were not consistent under their 1000 yards shelter compared to home testing of the same load. Maybe I was to close to the shelter posts or the echo from the roof at Rosedale and I got higher readings compared to home even discounting the atmospheric conditions, I will never know.

I have always relied on group shape and trend to do load development because graphed velocity data looking flat spots to compare with resonant nodes doesn't always correlate. Yet when they do my confidence rises. Certainly a false 30 fps could pop you over the energy limits on some ranges if your node lies close to the energy limit. It would certainly divert your attention away from a prospective group. That's why I always trust the paper and do initial load development at 140 yards as I have suggested for 20 years, outside the influence of aerodynamic jump etc. If your results can be duplicated and records are kept of groups then better decisions can be made.

Don't know how to convince people to move beyond 100 yard testing with boat tail bullets.

[pjifl]

Willadia wrote

Don't know how to convince people to move beyond 100 yard testing with boat tail bullets.

We will never get much sense across while everyone believes all the crap on glitchy web sites - many of which are simply another form of advertising. Very few people these days are after truth.

Peter Smith.

[AlanF]

...Don't know how to convince people to move beyond 100 yard testing with boat tail bullets.

Ok Dave. I am confused by your implication that aerodynamic jump lessens after 140 yards? Can you please give us a clear and focussed explanation of how you arrived at what shall be known as "Williamsons's number" i.e. 140 yards.

[Gyro]

I have a mates Labradar to borrow and I believe every time I do I end up wanting to throw a brick at it !!!!!! I would not be surprised if I'm a big part of the problems I have with it but despite that I just don't trust it now. Anyway, the last time I borrowed it was to get a load with an FTR gun with the 200.20x boolits, just so I could get on the paper at 1000 yards at a shoot I was aiming to go to. And sure enough the bloody LR did not register all shots but it provided enough info to get me on the paper at 1000 yards when I got to the shoot.

So off I went to the 1000 yard shoot and my group had massive vertical !!! The reason I am convinced was because the SMT system ( electronic scoring system ) was not set up properly.

I think what is happening in todays world where we have so many 'distractions' is that the proper time, both mental and physical, is not being given to properly understand and manage these devices ?????

[Pommy Chris]

Willadia wrote

Don't know how to convince people to move beyond 100 yard testing with boat tail bullets.

We will never get much sense across while everyone believes all the crap on glitchy web sites - many of which are simply another form of advertising. Very few people these days are after truth.

Peter Smith.

I have always tested at 200 yards, if I can make one hole at 200 yards again and again it has always worked further out. I agree 100 yards proves nothing.
Chris

[Pommy Chris]

Yep Chris, I was having a bit of fun even with the video. I only use chrono's et al, as a rough guide. There maybe something in that 30 fps anomaly as you suggest as Peter has indicated with the echo strength and the cosine error. I make a point of getting the muzzle as close as possible to the LR at its mid point on the side of it. On balance I think you had a LR glitch. If it continued to give errant readings on an open range, I would want a replacement. I'm going to take up Barry's suggestion and look through the casing of a ball point pen because I think alignment is critical.

I do note that my LR was within a few fps of the Rosedale club's MS a couple of years ago shooting in the open. At another time, my readings were not consistent under their 1000 yards shelter compared to home testing of the same load. Maybe I was to close to the shelter posts or the echo from the roof at Rosedale and I got higher readings compared to home even discounting the atmospheric conditions, I will never know.

I have always relied on group shape and trend to do load development because graphed velocity data looking flat spots to compare with resonant nodes doesn't always correlate. Yet when they do my confidence rises. Certainly a false 30 fps could pop you over the energy limits on some ranges if your node lies close to the energy limit. It would certainly divert your attention away from a prospective group. That's why I always trust the paper and do initial load development at 140 yards as I have suggested for 20 years, outside the influence of aerodynamic jump etc. If your results can be duplicated and records are kept of groups then better decisions can be made.

Don't know how to convince people to move beyond 100 yard testing with boat tail bullets.

Re testing as I said to Peter, I test at 200 simply as 100 is too close to give meaningful results, if a gun shoots one hole at 200 I know it will perform much further out. I have retested on occasion at 300, but this needs to be done last thing in evening when range goes dead still so pain to do.
Re the Lab radar the really high reading was only once, but even with other peoples Labs I have seen odd readings that I dont believe. I remember getting ready for Canada and a practice in Brisbane. I was shooting 1,000 yards and all was going well X,X, then a shot that the Lab said was 38 fps lower, I remember saying that is going to be a low shot looking at the speed, the shot came up another X so I think the Lab was probably wrong.
Not sure what causes these things but angle is my bet, but as you said maybe something else as you suggested.
Chris

[AlanF]

...I agree 100 yards proves nothing.
Chris

Opinions vary on that. Some very accomplished shooters swear by 100yd load development. I've always preferred 500 ladders as a minimum, but desperate times call for desperate measures.

[Pommy Chris]

...I agree 100 yards proves nothing.
Chris

Opinions vary on that. Some very accomplished shooters swear by 100yd load development. I've always preferred 500 ladders as a minimum, but desperate times call for desperate measures.

I can put all through one hole at 100, but at 200 cant, then develop the load and one hole at 200.
100 is too close to prove gun will shoot right out to 1000.
If you can shoot one hole at 200 and load down and up is a clover leaf, at 100 all three loads are one hole, which do you choose?
If you are shooting one hole at 200 then at 300 you are all X's, one hole at 100 does not mean one hole at 200, this is the point.
Chris

[AlanF]

Chris,

Personally, I don't think your point is a good enough reason to rule out 100yd testing. If I was getting one hole groups at 100 and wasn't satisfied (unlikely) then surely the shape of the holes would reveal enough. One of the best known advocates of 100yd load development is US F-Open shooter Eric Cortina. His performances at the last two FCWCs and other big North American shoots speak for themselves. In FCWC 2017 he finished 5th with a very high V count - so he definitely knows how to tune a load. That said, if there is convincing evidence that boat-tail bullet paths are more erratic at 100yds then say 200, then that would be of concern, hence my request to Dave Williamson.

[Gyro]

I must be missing something because I've never shot a one hole group at 100 yards, hence I can get a very good idea at that distance of many things that are happening.

[Rich4]

I must be missing something because I've never shot a one hole group at 100 yards, hence I can get a very good idea at that distance of many things that are happening.

I’m very glad to hear that, I thought it was just me
That being said I believe Williada has a proven reason for advocating 140 yard minimum testing, also recorded here but I cannot remember the thread, great to see some discussion going on, especially by very knowledgeable members, I’d like to start a new thread on ES-SD reduction strategies however I be no idea how, some help please?