Chronographing questions

[5RWill]

Chronographed some loads today, and i got a 77fps difference overall out of 10 shots. Which was a little big to me. For the most part my shots were in the 2870s-2880s. But i would have some jump up to 2924 and 2942. So i'm thinking maybe i've got 1/10 thousandths of a gr of powder off or something. But then i think what if it's the chrono? Anyway we averaged out 2898.

I'm also wondering how many shots everyone uses before they get their average?

Anyway i'm wondering if these variations of fps will equate to misses down range?

I will eventually get a oehler 35p but right now i'm using a friends F1 chrony, so until then this is all i got.

 

[Cheetah]

Re: Chronographing questions

I found out with my Chrony, slight lighting variations (a cloud passing over the sun) can cause pretty drastic jumps in my readings.

I try to chrony on overcast days, just lends more even lighting to the sensors. I also use a white grocery bag covering from front to rear sunshade supports of my chrony in place of the plastic sunshades.

If you're new (or even experienced) at reloading, it could be an issue there. I've definitely noticed my shot-to-shot consistency get increasingly better the more I load and the more I work out my procedures behind the bench.

Also, I have heard more than one report of chrony's giving horribly inconsistent readings, so that <span style="font-style: italic">could</span> be your issue as well. I wouldn't put a ton of stock in that if you're getting pretty average strings though. I usually load 5 test loads, starting low and increasing .1gr of powder each different load, ten rounds of each test. Average them out, check brass, pay attention to consistency and accuracy across the lot. If I feel like I have a winner out of the bunch, I'll load 50 more and test it for accuracy, reliability and consistency before I load it en masse.

 

[Sportin Wood]

Re: Chronographing questions

I wouldn't put too much thought into 77fps difference. If it was 100-200 different then yeah, something is up. The powder trickler you used could've thrown a hair touch more or less, you could've seated one a hair less than the others, but if in 10 rounds you have two that goe haywire, don't do too much fretting unless you run cometitions out to 600 yds and are a reloading freak....

 

[AKAce]

Re: Chronographing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: StanwoodSpartan</div><div class="ubbcode-body">I wouldn't put too much thought into 77fps difference. If it was 100-200 different then yeah, something is up. The powder trickler you used could've thrown a hair touch more or less, you could've seated one a hair less than the others, but if in 10 rounds you have two that goe haywire, don't do too much fretting unless you run cometitions out to 600 yds and are a reloading freak.... </div></div>

Really ? With a Typical .308 that equates to about 27" change in drop @ 1000, 5" @ 500 ... a full MOA

OP, tighten up your loading practices. Read the Stickies by Tresmon.

 

[5RWill]

Re: Chronographing questions

Will do. I usually do things very slow, because in all honesty i want to be as precise as humanly possible. Thats what i was thinking is maybe i trickled 1/10 of a grain too much on some loads. My reloading setup isn't ready yet. So i use my friends. Also wondering if i should invest in electronic scales or keep regular scales like i have. Luckily i got all my dads old reloading stuff and i haven't had to really buy that much. Just trying to find a bench or build one and i'll be on my own. This gun is for 1000yds shooting.

Any links to Tresman's stickies? I searched tresman and only came up with 2 threads.

 

[aggiesig]

Re: Chronographing questions

go to the reloading section and they are all at the top....

There are 4 or 5 sections that all cover different steps in the process

 

[5RWill]

Re: Chronographing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: aggiesig</div><div class="ubbcode-body">go to the reloading section and they are all at the top....

There are 4 or 5 sections that all cover different steps in the process</div></div>

Ah thought too hard about it. Thanks. So all in all its not the chrony getting different variations? I have no doubt i need to tighten up my tolerances, but i was just wondering?

 

[gstaylorg]

Re: Chronographing questions

How does your actual drop at a specified range compare to the drop calculated for that range using your average MV in the JBM ballistics program (ie. high, low, dead on)? Also, if you're really getting that much variation in MV across a 10-shot string, you should probably be seeing a fair bit of vertical stringing in your POI at the target as well. If not, it is more likely a variance in the chrony reading/measurement rather than variance in the actual MV.

 

[5RWill]

Re: Chronographing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: gstaylorg</div><div class="ubbcode-body">How does your actual drop at a specified range compare to the drop calculated for that range using your average MV in the JBM ballistics program (ie. high, low, dead on)? Also, if you're really getting that much variation in MV across a 10-shot string, you should probably be seeing a fair bit of vertical stringing in your POI at the target as well. If not, it is more likely a variance in the chrony reading/measurement rather than variance in the actual MV.</div></div>

I only had 2 in the 2900s for the most part they were in the 2880s. Here's my group, 9 shots in the one huge hole, 2 flyers 2 to sight it in. I'll have to look at JBM and compare it.

 

[vman]

Re: Chronographing questions

Blackops_2

A few things to take into consideration when using a chrony...

- you want to shoot right in the middle of the two arms on either side and about 6 inches above the sensor... it can be a little bit higher but I find its important to be in the middle.

- If its a sunny day with clouds, you might find in cloud cover you get a good reading, but when clouds pass all of sudden the readings change

- If you keep both eyes open when look thru the scope, you should be able to visualise the chrony out of focus whilst having a sight picture of the target overlapping. This gives you an indication of whether your in the middle or not. Make sense?

I have been plagued recently by a chrony that missbehaves with varying light conditions and nearby shooters muzzle blasts. I have come up with an idea that I have not tested yet but hope to soon.

What I plan to do Is obtain some thin white cloth similar to the material used in T-shirts or maybe even thin table cloth. I figure if i make a "sock" for my chrony that encloses whole unit into a triangle shape, it will provide a uniform input of light and give protection from muzzle blasts.

I hope this works. My idea is that the screen will block strong direct overhead light that bypasses the skyshades.

What do you think.

 

[5RWill]

Re: Chronographing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">Blackops_2

A few things to take into consideration when using a chrony...

- you want to shoot right in the middle of the two arms on either side and about 6 inches above the sensor... it can be a little bit higher but I find its important to be in the middle.

- If its a sunny day with clouds, you might find in cloud cover you get a good reading, but when clouds pass all of sudden the readings change

- If you keep both eyes open when look thru the scope, you should be able to visualise the chrony out of focus whilst having a sight picture of the target overlapping. This gives you an indication of whether your in the middle or not. Make sense?

I have been plagued recently by a chrony that missbehaves with varying light conditions and nearby shooters muzzle blasts. I have come up with an idea that I have not tested yet but hope to soon.

What I plan to do Is obtain some thin white cloth similar to the material used in T-shirts or maybe even thin table cloth. I figure if i make a "sock" for my chrony that encloses whole unit into a triangle shape, it will provide a uniform input of light and give protection from muzzle blasts.

I hope this works. My idea is that the screen will block strong direct overhead light that bypasses the skyshades.

What do you think.</div></div>

For the most part seems like the sock idea would work. Can't hurt to try though right?

When we chronographed my loads it was a cloudy day, almost started raining on us before we got the chrony out. So i can't blame it on the sun. For the most part we shot through the center of the chronograph, but we did get 2 errors, and it failed to read. I'm definitely going to tighten up my tolerances reloading next time, and start saving up for a oehler. Only problem is i'm broke and am in the mist of building a mk12 mod 1. Just got my upper in so i need to finish it. While at the same time finish my bolt rifle, build a range, and find a reloading table for my press and everything. I'll say one thing it sucks being 20 and loving to shoot haha. It's hard as hell for me to get everything going on my own. Wish my dad would get back into it.

 

[gstaylorg]

Re: Chronographing questions

Looks like you do have some vertical stringing, but it's really hard to tell whether that is the MV, driver, etc. It might be more revealing to try it out at greater range, where the stringing should be more pronounced. Running your hi/lo numbers through JBM should give you an idea of how far out you'd need to go to observe vertical stringing (if it's happening) due to changes in MV that would be statistically greater than your normal accuracy/precision. If you decide to go to that length, you might want to keep track of individual shot POI and see if it correlates with any major deviation in MV as measured by your chrony.

 

[5RWill]

Re: Chronographing questions

I'll be doing it in the next day or so. Weather for the past 2 days sucks. So tomorrow i'll shoot at 200 or 300 yds see what happens.

Also thanks to recommending those stickies by tresmen great read and very valuable.

 

[vman]

Re: Chronographing questions

I hear ya dude... im 27.

Money aint easy to come by.

 

[5RWill]

Re: Chronographing questions

Well the chronograph wasn't far off even if it was wrong. I had adjusted for a 5mph crosswind and used my overall average fps which is was 2898. But MV isn't consistent, this group is a 200yds. Definitely have some vertical stringing. Kinda disgusted with the results. Sure i'm not 100% steady but i had a rear rest and was rested enough IMO. Definitely going to tighten up everything, regardless of how long it takes. I'm looking to switch primers to a softer charge i've been using magnum primers, going to try winchester large rifle, Federal gold match, and CCI benchrest. Pair that with tighter preferences when loading it everything should tighten up.

 

[vman]

Re: Chronographing questions

Oh yeh man... Try out the Fed210M primers I have used those with good results.

Occasionaly scored the odd 1" group at 400 yards. Best to date was 0.27" 3 shot group at 375 yards.

200 yards is pretty easy to get 1" groups, so i also agree that you probably should be getting better results.

You know, if your smack bang in the middle of a node 1/10th grain variations dont make that much of a difference... or not at 200 yards anyway.

Whats the rifle/load combination? Those holes dont look like .30cal

 

[5RWill]

Re: Chronographing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">Oh yeh man... Try out the Fed210M primers I have used those with good results.

Occasionaly scored the odd 1" group at 400 yards. Best to date was 0.27" 3 shot group at 375 yards.

200 yards is pretty easy to get 1" groups, so i also agree that you probably should be getting better results.

You know, if your smack bang in the middle of a node 1/10th grain variations dont make that much of a difference... or not at 200 yards anyway.

Whats the rifle/load combination? Those holes dont look like .30cal
</div></div>

There is one impressive plus to me. I should've circled it but i didn't think about it. I counted my shots which was 12, and the tightest group in the pic up above, is actually 4 shots not 3. 2 are damn near in the same hole, which makes me a little happier. Like i said and someone on thefiringline mentioned, a softer primer charge would help regulate steadier velocities also, so i plan on loading some groups with different primers and testing them out.

Load data:
Winchester large rifle magnum primers (going to change this)
Nosler custom .308 brass
Lapua 155gr scenars
OAL 2.800.

Rifle: Model 700 5R bedded in a McMillan A-5.

 

[5RWill]

Re: Chronographing questions

Well when the loads are similar in velocity they sure are accurate. As you can see @ 300 vertical stringing gets worse but the last 3 rounds i shot must've been extremely similar.

 

[vman]

Re: Chronographing questions

You are around the same area I am...

Went shooting with a friend today. Wind was a bit deceptive.

46.3gr Varget, Lapua 155 Scenar, Lapua Brass on about its 7th firing, Federal 210M primers.

This was shot at 300 yards.

The middle line of targets was shot either 46.5 or 46.1, I cant remember.

The bottom 2 are 46.3.

It was pretty hard to see miss shots as it fairly warm, and this makes it hard to spot holes on white backgrounds (no spotting scope). And as I said wind was all over the place.

Bottom right group displays less than 1/2" of vertical at 300 yards. I have had this same load give me 0.25" group at 400 before but that was when the universe was smiling at me!

 

[5RWill]

Re: Chronographing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">You are around the same area I am...

Went shooting with a friend today. Wind was a bit deceptive.

46.3gr Varget, Lapua 155 Scenar, Lapua Brass on about its 7th firing, Federal 210M primers.

This was shot at 300 yards.

The middle line of targets was shot either 46.5 or 46.1, I cant remember.

The bottom 2 are 46.3.

It was pretty hard to see miss shots as it fairly warm, and this makes it hard to spot holes on white backgrounds (no spotting scope). And as I said wind was all over the place.

Bottom right group displays less than 1/2" of vertical at 300 yards. I have had this same load give me 0.25" group at 400 before but that was when the universe was smiling at me!
</div></div>

Very nice!, hell now i'm almost out of 155gr scenars. Going to try some different primers and see what velocity readings i get on the groups. Also plan on ordering some berger 175gr BTHP (BC .515) and will see how they do with the 11.25 twist rate.

 

[LoneWolfUSMC]

Re: Chronographing questions

I use the cheapest Shooting Chrony they make.

It works for my purposes. When I actually take time and crank out some top notch ammo my ES is around 10fps. I have had it drop below that over a five shot group regularly, but if I average it over the whole lot its usually around that.

That is simply throwing close and trickling up. No special mojo. FL sizing with Federal 1x brass. Federal GM210M primers.

The last load I ran like this was 43gr of IMR 4064 and a 168gr Nosler CC. Seated to the exact same dimension off the ogive as 168gr FGMM.

I don't do anything special with the Chrony. I set it at 10 feet and use the factory screens. I just try not to use it when it's raining.

 

[Lowlight]

Re: Chronographing questions

I hate my Oehler 35P, it hasn't been right from the beginning, I might have gotten about 1 year out of it before it needed to be addressed. To this day it sits on the floor in my garage in near pristine conditions until i finally decide to try out their customer service. My #3 switch is fubar, in fact I suspect the switch itself is shot.

From there I moved a PACT Pro, that worked great until it didn't. Not that stopped working...

At RO I have a CED M2 w/ IR screens, that has been working well with little care. We use it quite a bit and it's been working well.

Last month I bought a PVM 21 hoping it will replace my Oehler and PACT back home, we'll see how it works...

in the end, doesn't matter what you spend, if it works, go with it.

 

[5RWill]

Re: Chronographing questions

Good to hear, for now i'll continue using my friends chony F1 until i get everything complete i got to do on the list. Which includes reloading setup, range, and a SPR.

 

[mouse07410]

Re: Chronographing questions

Lowlight,

As I understand, the trick with "cheaper" chronographers is getting them calibrated correctly. And the "folklore" says that Oehler comes pretty well calibrated from the factory.

Could you please comment on:

1. How to figure out/test/whatever the calibration of a chrono? If it consistently says e.g. "2590fps" - what confidence does one have that it's not reading say 50fps high?
2. How consistent in your experience are those chronographs that you used (e.g. when they give you velocity spread - how do you make sure it's not the chrono erring high and low taking readings)? (I'm contemplating Oehler to supplement or replace my Pro Chrono Digital, so hearing of your experience helps.)
3. Since one must have the <span style="text-decoration: underline">true</span> velocity to make a meaningful long range trajectory prediction - given the uncertainties of the current consumer-grade chronographs what's your word of advice to beginners?

Tnx!

 

[gstaylorg]

Re: Chronographing questions

Mouse,

Definitely not trying to imply I know more about this than others here, but I've spent a lot of time thinking about this issue and trying to learn more about how my beta chrony functions, so I'll take a crack at responding to the first two parts of your question.

a) One way to try to check the MV readings from a shooting chronograph is to compare your <span style="font-style: italic">actual</span> drops at some distance to the drop <span style="font-style: italic">predicted</span> by a ballistics program such as JBM. At 600 yd, JBM gives the drop for an SMK 175 gr BTHP as 105.2" or 4.9 mil at 600 yd (using the Litz BC, 70 degrees, 2.4" sight height, air press = 29.92, MV = 2540 fps). At a MV of 2590 fps, the drop is predicted to be 100.4"/4.6 mil under the same conditions. If someone is confident enough in the precision of their shooting, they can get a feel for whether their chronograph is reading hi/lo by how their actual drop compares to the drop predicted for the MV given by their chronograph.

b) The SD and ES given by any chronograph are calculated directly from the numerical data collected by simple mathematical algorithms. These numbers should be absolutely correct for the <span style="font-style: italic">actual</span> values collected in any given string (data set). However, like any other data set, if the collected data are lacking in accuracy or precision, then any values derived from them by an algorithm will also be in error. Take the following two 10-shot MV strings for example:

<span style="text-decoration: underline">String 1</span>
2591
2597
2583
2601
2588
2576
2593
2596
2591
2584

<span style="text-decoration: underline">String 2</span>
2541
2547
2533
2551
2538
2526
2543
2546
2541
2534

The values in String 1 differ from those in String 2 only in that they are each 50 fps higher. The mean, standard deviation, and extreme spread for these two strings are as follows:
String 1: mean = 2590, SD = 7.5, ES = 25
String 2: mean = 2540, SD = 7.5, ES = 25

What this demonstrates is that as long as the chronograph always gave a reading <span style="font-style: italic">exactly</span> 50 fps high, it would only affect the mean MV value determined from the string, but not the SD or ES.

However, it seems pretty unlikely that a chronograph under actual use would read every velocity high (or low) by exactly the same amount every time. So in reality it is more likely that MV, SD, and ES would all be affected by a chronograph that gave inconsistently high (or low) readings, even if it tended to be one or the other.

By analogy to comparing actual drops to those predicted from a ballistics program, one way to get an idea of how well the chronograph is performing in terms of hi/lo readings is to record individual shots at some distance to the MV recorded for that shot. If they are <span style="font-style: italic">real</span>, large changes in measured MV would be expected to give noticeable vertical stringing if the range is great enough. The vertical stringing should correspond to the extremes (hi/lo) in MV. As with comparing actual and predicted drops, the range needs to great enough to outweigh the normal group spread for a given shooter, and of course, the precision of the driver needs to be sufficient for such a test to give any useful information (LOL).

Even though I enjoy thinking and learning about issues like this one, I have to tell you that in reality, I don't worry about it too much at the range any more, primarily because I realized the major limitation in my shooting was me, not the accuracy of my chrony. Just to check it, I have done what I described in a) above for several different .308 factory loads that I chrono'd. The drops calculated by JBM for the MV values given by the chrony were very good for every one at 600 yd. I don't know whether that means my chrony is well-calibrated, but the data it generates seems to work, so now I just go with it. It's also possible that the chrony is behaving so well only because I accidentally shot the support wires out on one side a couple months ago and perhaps it fears further retribution if it acts up (LOL).

FWIW, the info that came with the beta chrony states that it has an accuracy of 99.5% or better. That translates to +/- ~13 fps for an avg MV of 2500. If you believe the statement in the product manual, of course. How the company actually calibrates the instrument, I have no idea. That was one reason I tried to compare actual to predicted drops, just to get an idea of whether it was in the ballpark. Since doing that however, I decided I have so many more important things to worry about (like basic shooting fundamentals) that I quit worrying about whether my chrony was accurate so much anymore and just use the values it gives and then determine actual drops with that particular load. If someone's chronograph was consistently high or low, it wouldn't be a big deal to back-calculate approximately how much it was off, then re-run the MVs through JBM, or just know that you have to increase (or decrease) the JBM predicted drop by that correction factor, which can save a lot of time and ammo over the long run.

 

[vman]

Re: Chronographing questions

Frank,

real shame to hear that your Oehler is playing up. Would be worth getting it fixed imo.

I have heard only good things about the CED m2

 

[5RWill]

Re: Chronographing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: vman</div><div class="ubbcode-body">Frank,

real shame to hear that your Oehler is playing up. Would be worth getting it fixed imo.

I have heard only good things about the CED m2</div></div>

I had a CED m2 but never got around to using it. Sent it back to put the money into a shotgun. When i look at mine it will most likely be between pact or CED. The CED does feel cheaply made though or it kind of did to me.

 

[vman]

Re: Chronographing questions

Yeh I have played with a CED and I must admit it came across the same way to me.

I cant recall hearing any bad stories about them tho.

I have heard a lot of bad things about shooting chrony units.

I have had a defective unit before, and my current unit has a personality that would challenge that of Charlie Sheen... it thinks its winning but its not.