ballistic chronograph

[Ground_Loop]

Any of you shooters ever build a ballistic chronograph.  I'm interested in getting an understanding of the actual sensor loops (non optical).  Ultimate goal is to have battery powered sensor loops down range communicating to local readout via blue tooth.  Programming and electronics I can handle.  At this point I just need to understand how the sensor loops work.

[tautech]

AFAIK there are only 2 types, optical (photocell) and doppler.
The photocell units I've used and seen used have 2 or 3 sensors and doppler types are placed near the shooter and track the projectile for its velocity.

Are you investigating using inductive proximity sensing ?

[edy]

Would it be possible to put 2 large induction coils several feet apart and shoot a projectile through them? Have them connected to an Arduino or RasPi and see if a "blip" shows up when your projectile travels through it? Then take time diffference to determine velocity? Most projectiles being lead I am not sure what magnitude of effect it would have on the induction loop, if any, and the huge speed it is travelling past may not even register. I mean, if you have air coil with some current going through and then you stick an iron rod into the middle, it will alter the current for a moment and then equalize again to a steady state once the iron magnetizes. Then when you remove iron and get back to original air centre it will again change current for a moment and settle back, right? If these changes could be detected with this be enough? I'm thinking for a pellet gun that shoots .177 lead. Obviously copper tipped or full metal jacket ammo would have different effects but still create a momentary change in current. You would have to be accurate to shoot through the middle and not blow up your loops.

There is one other possibly dirt-cheap mechanical solution. Have 2 discs that rotate say a few feet apart coupled to each other. The projectile hits and passes through the first disc and then hits and passes through the second disc. You know the rotation speed of your discs and you check the angular difference between the puncture holes in each disc. You then calculate based on rotation speed, angular difference and spacing between the discs how fast the projectile would need to be.

[tautech]

There is one other possibly dirt-cheap mechanical solution. Have 2 discs that rotate say a few feet apart coupled to each other. The projectile hits and passes through the first disc and then hits and passes through the second disc. You know the rotation speed of your discs and you check the angular difference between the puncture holes in each disc. You then calculate based on rotation speed, angular difference and spacing between the discs how fast the projectile would need to be.

Trouble with this ^ is purists only wanna fire as few shots as necessary as rifle barrels have a finite life.

With a sensor chronograph you can collect velocity, its spread and test for grouping for successive shots.
Before the days of optical sensors bullets would break 2 very fine wires and velocity was calculated from the distance and time interval between them.

[Szumi]

I believe the magnetospeed is inductive.  I don't care for it as it needs to be attached to the rifle's barrel thus changing the harmonics. 

So far,

Optical
Radar
Wire break
Induction
Not sure what to call that synchronized disk method.

I'll add ballistic pendulum.  Old school.

[edy]

According to Wikipedia it is called a "wheel chronometer" invented by Alessandro Vittorio Papacino d'Antoni and published in 1765. Now that is old school! There is also one by Grobert, a colonel in the French army, circa 1804.

Another type of design on that Wikipedia page on chronometers describes 2 screens made of fine copper wire mesh. Breaking the first screen started charging a capacitor and breaking second would stop it. Measuring accumulated voltage and rate of charge would give you time.

[rstofer]

3 of my 4 chronographs use an optical system looking for the glint off the bullet as it pass over the sensor.  The CED Millenium 2 Chronograph uses this principle:

https://www.midwayusa.com/product/101506602

The sensors are available for replacement:

https://www.doublealpha.biz/us/ced-m2-replacement-sensor

I don't know how much the OP can save on a $200 gadget if time has any value at all.

My Magnetospeed uses inductive pickups and is clamped to the barrel.  Whether that changes point of impact very much will depend on the barrel.  Who cares?  I separate ballistics testing from zeroing - two entirely different things.

My next chronograph, if any, will be the Labradar because I can get downrange velocity.  One thing is certain, the Magnetospeed means I don't have to hold up the entire firing line while I mess around getting the downrange screens adjusted.  What a PITA!  Not so much if you shoot by yourself, I suppose.

https://mylabradar.com/

Coriolis can have a huge influence on point of impact, equivalent to perhaps 70 fps of velocity at 1000 yards depending on the round.  Nearly 1 MOA in this video:



Velocity, by itself, is only a small part of the equation.

If you're looking for a great ballistics app, consider Strelok Pro

http://www.borisov.mobi/StrelokPro/android/

See the last question on the home page regarding 'truing' where the muzzle velocity is back-calculated.

[tautech]

I don't know how much the OP can save on a $200 gadget if time has any value at all.

$110
http://www.shootingchrony.com/products_SCMMCM.htm

While some consider these a POS we tried 2 back to back and the results were surprisingly accurate.

My next chronograph, if any, will be the Labradar because I can get downrange velocity. 

Yes but if you have muzzle velocity, a ballistics program and enough range to measure POI trajectory, corrections can be made in the program to ballistic coefficients to give very accurate real trajectory results at extended ranges.

[rstofer]

I don't know how much the OP can save on a $200 gadget if time has any value at all.

$110
http://www.shootingchrony.com/products_SCMMCM.htm

While some consider these a POS we tried 2 back to back and the results were surprisingly accurate.

My next chronograph, if any, will be the Labradar because I can get downrange velocity. 

Yes but if you have muzzle velocity, a ballistics program and enough range to measure POI trajectory, corrections can be made in the program to ballistic coefficients to give very accurate real trajectory results at extended ranges.

Strelok Pro will do that!

My only complaint with the Shooting Chrony is that the high dollar stuff is downrange (speciically on the F1 model, I don't know anything about the F1 Master) .  I realize that NOBODY will ever fess up to shooting the electronics but I have seen tangible evidence that it occurs.

The range where I shoot rents the Shooting Chrony - they have several and they work very well.  Right up until somebody puts a bullet through the display.  Nevertheless, they are highly regarded chronographs.

I keep a "Come Up" card for .308 168 gr and 175 gr in my wallet.  I suppose some people would think that is a little odd but it seems important to me to know that the 500m Ram needs 5.3 mils or 53 clicks.  If I'm going to impress my grandson, I need to hit it on the first shot!  Do-overs don't count!

[tautech]

My only complaint with the Shooting Chrony is that the high dollar stuff is downrange (speciically on the F1 model, I don't know anything about the F1 Master) .  I realize that NOBODY will ever fess up to shooting the electronics but I have seen tangible evidence that it occurs.

The range where I shoot rents the Shooting Chrony - they have several and they work very well.  Right up until somebody puts a bullet through the display.  Nevertheless, they are highly regarded chronographs.

Placing them close to the bench has risks too and a guy I lent mine to had it too close to the loud end of a 300WM and shattered the plastic LCD display overlay. He didn't RTFM ! 

I keep a "Come Up" card for .308 168 gr and 175 gr in my wallet.  I suppose some people would think that is a little odd but it seems important to me to know that the 500m Ram needs 5.3 mils or 53 clicks.  If I'm going to impress my grandson, I need to hit it on the first shot!  Do-overs don't count!

Trajectory cards are common here when taking game at extended ranges however some shooters prefer cell phone apps as you can add angle of departure ......not that it matters much for larger game.
With these cell apps you can enter the exact distance after ranging it for precision hits on small critters.

Good luck with the youngen and teach him well as precision field shooting requires much time at the bench first to learn the art. For heavens sake don't expose him to too much recoil before he is ready to handle it or it will only teach him to flinch.......a habit that I couldn't break until I got an accurate 223.

[rstofer]

Good luck with the youngen and teach him well as precision field shooting requires much time at the bench first to learn the art. For heavens sake don't expose him to too much recoil before he is ready to handle it or it will only teach him to flinch.......a habit that I couldn't break until I got an accurate 223.

The young one (now 21) shoots well.  He takes all the money at the monthly Military Bench Rest competitions using my M1A SuperMatch (.308).  These matches use reduced scale 600 yard targets shot at 100 and 200 yards.  Still, it takes a pretty tight group to max the course.  There is another fellow, a former Army Marksmanship Unit shooter who can outshoot him when he shows up but that's about it.  I shoot a battle grade M1A so there's not much competition between us.  I get to pay the entry fees, he keeps all the winnings!  There's something wrong with that picture.

Yes, I've taught him well.  His favorite handgun in my Sig 1911 in .45 ACP and he shoots it very well.  Good eyesight and no 'quivers' is a real plus.

Off and on, we've been shooting together since he was 10 and we still enjoy a day of shooting .22 LR at very small silhouettes at 50 yards.  I like shooting the small bore rifles.   Everything is much more relaxed on the rimfire range.

[tautech]

 
A buddy shoots Mil comps too and turned up at one a year or two back with his .222 Sako Vixen and of course cleaned them all up despite the howls of protest that a Sako Vixen wasn't a mil grade weapon. When he produced proof that they were once issued to some IIRC African nation there was nothing they could do but change the rules to exclude him from their next comp. 

[edy]

And here I am wanting to build a chrony for my .177 pellet gun (Ruger Air Hawk with scope).... 

I may be better off making a pendulum. Cheap and probably come close, just have to figure out a way to mark the height reliably without introducing too much resistance. Something like this may be do the trick (and just record it with a camera):

[rstofer]

A buddy shoots Mil comps too and turned up at one a year or two back with his .222 Sako Vixen and of course cleaned them all up despite the howls of protest that a Sako Vixen wasn't a mil grade weapon. When he produced proof that they were once issued to some IIRC African nation there was nothing they could do but change the rules to exclude him from their next comp. 

One military style match around here wants weapons up through WWII only.  The M1 Garand is in, the M14 (actually, it's derivative, the M1A) is out.  Officially...  It turns out that the M1A shooters are required if they want to fill up the firing line.  So we get to shoot!  Scored separately...

One of the other matches has a similar rule about  "issued" rifles.  One day I'm going to show up with my Steyr SSG - they are used all over the world for police and military.  Not all that common but it shoots a dime group at 200m right out of the box.  My kind of rifle!

[rstofer]

And here I am wanting to build a chrony for my .177 pellet gun (Ruger Air Hawk with scope).... 

I may be better off making a pendulum. Cheap and probably come close, just have to figure out a way to mark the height reliably without introducing too much resistance. Something like this may be do the trick (and just record it with a camera):

Is a cell phone video fast enough?  Some Androids will go to 240 fps.

 I might put a potentiometer at the pivot and do a little peak capture of the resulting voltage.  Maybe an optical encoder,,,

You might Google for 'pellet rifle chronograph'  There are quite a few projects, complete with videos.  It's been done!

https://hackaday.io/project/9378-diy-ballistic-chronograph

[Ground_Loop]

Thanks for all the replies.  I think I'm going to investigate an optical method after all.  I know I could just go out and buy something, but you know how it goes.

[tautech]

Thanks for all the replies.  I think I'm going to investigate an optical method after all.  I know I could just go out and buy something, but you know how it goes.

Keep in mind the background the optical sensor has to look at.
The cheap Crony's use a white plastic 'sky screen' that if removed on a clear blue sky day will cause it to miss most shots however on a full overcast day they will catch every shot without the sky screens attached.
Hunt out the link I offed a few posts back to see clearly the sky screens I talk about.
They are suspended above the optical sensors by ~18" V of 8g wire which also serves as a border in which the projectile must pass for it to be seen by the sensor.

My Crony works quite well enough that if anything happened to it I'd buy another in an instant as they are well priced.
Quite likely some one has already RE'd them and you can find the circuit online.
Good luck with your project however I'd much prefer to spend that time behind the trigger.