determining velocity

J

JoeyAld

Sergeant
Full Member
Minuteman
Apr 1, 2009
120
1
38
Tampa, FL
#1
Alright I am struggling to find a velocity. I do not have a chronograph so i was wondering if i am able to determine my velocities by another means. I do believe it can be determined I just need some guidance. I have the following information.

rifle is zeroed @100 yrds
@300 yrds I use 1.4 mils of elevation
@600 yrds I use 5.7 mils of elevation
@642 yrds I use 6.0 mils of elevation

if someone could help walk me through this I would be ever so thankful.
 
#3
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JoeyAld</div><div class="ubbcode-body">Alright I am struggling to find a velocity. I do not have a chronograph so i was wondering if i am able to determine my velocities by another means. I do believe it can be determined I just need some guidance. I have the following information.

rifle is zeroed @100 yrds
@300 yrds I use 1.4 mils of elevation
@600 yrds I use 5.7 mils of elevation
@642 yrds I use 6.0 mils of elevation

if someone could help walk me through this I would be ever so thankful. </div></div>

Help, head hurts...

We need a lot more info.

Rifle barrel length.

Ammo specifics.

Bullet and BC.

Temp, altitude and humidity.

I've got a lot spread sheets for different calibers and combos, like 250gr 338 Lapua Scenars at 2750, 2800 and 2850, so I have an idea, but I'm not going to start plugging in values that I don't even know what cartridge you're shooting.

A 155gr Scenar traveling at 2850 fps, according to my ModernBallistics freeware, shows 1.04 mils at 300 yds (100 yd zero, 65*, 0 asl) and 3.72 mils at 600 yds, so with that bullet, 2750-2775 fps might get your numbers?

A 175 SMK at 2600 fps gets me 1.36 mils at 300 yds and 4.65 mils at 600 yds, so maybe this bullet at 2550 might get your numbers?

It's a fool's errand, guessing without more info, however, my mother stills calls me a fool, so I'll play the game.

First, it looks like you're shooting a bullet that runs out of gas compared to the 155 Skinny and 175 MK, at least going by my program. While I can get the numbers close to yours at 300 yds, I'm flatter at 600 than you are.

I'm betting you're either shooting a sloppy BC bullet at higher velocities, like a 155 palma v.1 or you're shooting a higher BC bullet, but at a velocity below 2600 fps, perhaps out of a shorter barrel even?

Chris
 
#4
Re: determining velocity

okay yep i have lots of info.

cal. 308
Handload... 42.5 gr of Varget, 168 gr Nosler HPBT, federal primer,
bullet co. is .462 barrel length is 26inches.

temp was 58 degrees, alt. is roughly 250ft, and barometric pressure was 28.
 
#7
Re: determining velocity

The ONLY way to find velocity is to use a chronograph. That's part of why they are so popular.

NOTE: Let me edit that to say "The only practical way for most of us to determine velocity is with a chronograph." That rewording being needed to satisfy those playing trivial pursuit!
smile.gif
Or not, LOL?
wink.gif
 
#8
Re: determining velocity

If you can shoot a particular load out to a good distance, then backing out the velocity using a good ballistics program with tested ballistic coefficients is a perfectly valid way to determine muzzle velocity.

However, 600 yards is a bit too short to yield accurate data.
 
#9
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fuzzball</div><div class="ubbcode-body">The ONLY way to find velocity is to use a chronograph. That's part of why they are so popular. </div></div>
+1 but it you know your powder charge and bullet you should be able to look at published materials for that load and get close. Get the Velocity of a load and divide by the grain weight take that number and multiply it by the charge you are using and it will get you within a 100 or so feet per second but will in no way give you an exact speed which is what you need if you are looking to see if a bullet will go subsonic at certain ranges.

With your information I'm showing around 2635fps which jives pretty well with my recorded info with a 24" barreled Savage. Need to step it up a notch if you want to reach a 1000.
 
#11
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fuzzball</div><div class="ubbcode-body">The ONLY way to find velocity is to use a chronograph. That's part of why they are so popular. </div></div>

Are you trying to imply that one cannot determine velocity with a dopler radar? or a laser system? series of microphones, or by timing the projectile between thin sheets of metal? Or are you implying that when used thusly, they become a chronograph?

In actuality, one can deterine both BC and velocity from a large set of carefully collected drop data over different distance under known atmospherics. Given enough said data, one can even infer the drag model from the data used to give the projectile its BC.
 
#12
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fuzzball</div><div class="ubbcode-body">The ONLY way to find velocity is to use a chronograph. That's part of why they are so popular. </div></div>

I disagree. There are a number of ways to determine velocity. Even when using a good chrono you measure velocity some distance from the muzzle, and back calculate muzzle velocity.

A chronograph is convenient. Depending on make and model it may also be accurate. If it is not expensive it likely has poor precision, error prone, light sensitive, error prone, finicky, and did I mention error prone?

Please don't misunderstand, a chonograph can be a wonderful and useful instrument. Often however they just provide an opportunity to abuse statistics.
 
#13
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">In actuality, one can deterine both BC and velocity from a large set of carefully collected drop data over different distance under known atmospherics. Given enough said data, one can even infer the drag model from the data used to give the projectile its BC.</div></div>

Actually, no.

A BC is valid only with respect to a particular drag model.

If you have shooting data at a long distance, then you can specify a drag model in a ballistic program, and they use that program with that drag model to determine the BC.

But you can't determine both the BC and the drag model from shooting data.
 
#14
Re: determining velocity

I know i really should invest in a chronograph. Been looking towards the CED M2. But being a poor college student sucks! I appreciate the feed back i am getting. I had a buddy I was shooting with, he had some Previ Patterson match ammo and I fired 2 through my rifle and they hit about 4 feet low compared to my rounds with the same drop dialed in at 600 yards. A chrono is working its way into the budget!
 
#16
Re: determining velocity

"Originally Posted By: FuzzballThe ONLY way to find velocity is to use a chronograph. That's part of why they are so popular.
+1 but it you know your powder charge and bullet you should be able to look at published materials for that load and get close. "

Problem with that hopeful approach is that individual rifles can be so different that actual velocities may vary as much as 10% from published materials. A potential 10% error would seem to make such a guessing effort pointless.

Perhaps a radar gun could check bullet speeds but I doubt it and as an ex-USAF electronic tech, I know a bit about radar. I can assure you that trying to get a dopler return on a bullet would be a comedy even if the things were calibrated for such speeds. Someone with a good eye and quick hands might do it with a laser gun. Me, I'm gonna stick with my old PACT Pro.
 
#17
Re: determining velocity

<span style="font-weight: bold">Problem with that hopeful approach is that individual rifles can be so different that actual velocities may vary as much as 10% from published materials. A potential 10% error would seem to make such a guessing effort pointless.</span>

Thing is I find one with the same length barrel and it comes out within 100fps of my Chrony every time. Like I said it doesn't replace a chrony but it will give you an estimated guess. All of my rifles have always pretty much matched the hatch if I go through my manuals and find like set ups. I've also did a ton of testing with 223 with four different length barrels and got a pretty good ideal of how much speed I will lose per inch. Sierra uses a 26" Savage and I shoot a 24" and my speeds are for the most part within 50 fps of what they publish. Which with my 223 test 1" was between 25 and 30 fps per inch of barrel length. Other books use different lengths and a lot of them use rail guns. But what I told him will give him an Ideal of the speed because I've used it many times to start my loads on my rifles. Every rifle I own has a speed node or where the vibrations are right, that has the best accuracy. Once that speed is found and I want to try another powder I use that trick and work within a 2 grain charge and find what it likes without wasting a lot of powder and bullets.
 
#18
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I can assure you that trying to get a dopler return on a bullet would be a comedy even if the things were calibrated for such speeds.</div></div>

I can assure you that the military and some bullet manufacturers routinely use doppler radar in evaluating loads. Lapua even publishes data on their bullets measured with the radar.

See:

http://en.wikipedia.org/wiki/External_ballistics#Doppler_radar_measurement_method
 
#19
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JoeyAld</div><div class="ubbcode-body">I know i really should invest in a chronograph. Been looking towards the CED M2. But being a poor college student sucks! A chrono is working its way into the budget!</div></div>
Just eat bologna sandwiches twice a day for a month instead of what you usually eat then at the end of that miserable thirty days take the money you saved and go buy a decent chrono! Lol
 
#20
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ark. Trapper</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JoeyAld</div><div class="ubbcode-body">I know i really should invest in a chronograph. Been looking towards the CED M2. But being a poor college student sucks! A chrono is working its way into the budget!</div></div>
Just eat bologna sandwiches twice a day for a month instead of what you usually eat then at the end of that miserable thirty days take the money you saved and go buy a decent chrono! Lol </div></div>

how do you think i bought my rifle and scope
grin.gif


I have always looked through my manuals to get a sense of velocity. However, I was under the impression that they are not 100% and using the listed bullets BC is skewed by the manufacturer in order to make them look better then they are. I just figured somehow with knowing the drop between to distances a general velocity could be had; perhaps some nifty math formula? I do know I am going to have to add some powder in my loads to get out and touch something at 1000yrds, but I had hopes of working on technique and groups with this load to save the barrel life.
 
#21
Re: determining velocity

"Quote:I can assure you that trying to get a dopler return on a bullet would be a comedy even if the things were calibrated for such speeds.

I can assure you that the military and some bullet manufacturers routinely use doppler radar in evaluating loads. Lapua even publishes data on their bullets measured with the radar."

And I can assure you, you can't afford to buy or borrow one of those radars so that bit of info is irrelivant to the question, is it not?

And, if you get a local smokey to try it with one of his department's handheld radars he wouldn't get a valid reading, if anything at all.


Sheesh, the lengths some people will go to on an ego trip just to be a web "expert" on ridiculus points of far-out trivia!

Sticking to the OP's rational question should be enough for us, playing such a silly one ups-manship game is NOT helping him!
 
#22
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Sheesh, the lengths some people will go to on an ego trip just to be a web "expert" on ridiculus points of far-out trivia!</div></div>

You made a statement, which I quoted, which was simply wrong. In response, I made a correct statement and supplied a source. Whether doppler radars for ballistic purposes are widely available is not relevant.

I'm not trying to be a "web 'expert'" - you were wrong. If you don't like being corrected, make fewer errors.
 
#23
Re: determining velocity

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MitchAlsup</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fuzzball</div><div class="ubbcode-body">The ONLY way to find velocity is to use a chronograph. That's part of why they are so popular. </div></div>

Are you trying to imply that one cannot determine velocity with a dopler radar? or a laser system? series of microphones, or by timing the projectile between thin sheets of metal? Or are you implying that when used thusly, they become a chronograph?
</div></div>

Aw piss! Those are ALL chronograph systems when used as thus.

They're just a lot more expensive and probably more accurate.
 
#24
Re: determining velocity

"I'm not trying to be a "web 'expert'" - you were wrong. If you don't like being corrected, make fewer errors."

Joey Alds asked a rational question, I gave him a rational answers, you didn't.

You are a bit too full of yourself, your technically correct 'answer' was meant to be web show boating, not help. And it was presented in a clear effort to use your vast esotoric expertise in an irrelivant effort to put me down so you could stand tall.

As I said, I do know a bit about mil radar so your irrelivant info was no great surprise, and I don't get put down very easily. Enjoy playing with yourself.
smile.gif
 
#25
Re: determining velocity

You shouldn't be put down easily.

You should be put down hard.

I'm a happily retired electrical engineer, and I have forgotten more about radar than you've ever known. Four decades ago I bought a first edition of Merrill Skolnik's <span style="font-style: italic">Introduction to Radar Systems</span>. That was my first technical reference on radar systems, but not my last.

You thought that you'd get away with a silly comment that was obviously about police radar. You didn't. Life goes on.
 
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