Novice CHRONY user seeking feedback

[JamesD]

<<NOTE: this is NOT a reloading question.
<<It is a "generic" question about using a chronometer.
<<I posted it in the Reloading Forum because I figured this would be where most of the chrony users visited.
<<If this should be somewhere else, I invite a moderator to please move it.
<<Thanks.


Greetings All!

About a year ago I posted a thread here seeking recommendations for revolvers chambered in .32 H&R magnum. (easy to find in my profile if anyone interested)
I got TONS of GREAT information.
And ended up snaring me a brace of N.I.B. 431 P.D.s for a song. Not as sexy as some of y'alls revolvers you posted pictures of, but they're nice little revolvers that I'm quite pleased with.

Now...

I recently acquired me my latest little "tool" - a Shooting Chrony "Alpha Master" chronometer.

The first time I took it out I chronied some .32 H&R magnum ammo out of one of the 431 P.D.s, and I'm just trying to get the measure of this new tool, trying to figure what to make of the data I got, and just wondering if any of y'all experienced chronometer-ers would tell me how my data I got "looks" to you.

The ammo was:
Federal .32 H&R Magnum JHP #C32HRB, rated: 1120 muzzle velocity.
Shot from the S&W 431 P.D. (i.e. a 2" snubbie)

The summary data the Alpha Chrony gave for a string of this ammunition was:
Lo 862.7
Hi 916.8
Avg. 887.5
Spread 54.10
s.d. 19.59

How does that data "look" to y'all?

1- The velocity is WAY down from the "rated" velocity Federal publishes (887 vs. 1120).
Is that just due to firing it out of a 2" barrel?
Or...something else going on?

2- Is the "spread" and s.d. about what you guys are used to seeing? Or... not?

Like I said, this was the first time out with my new chrony and I'm just trying to get the measure of it, how it works, what to expect, is the chrony functioning properly, etc.

Thanks for any comments.

Best regards,

JamesD

 

[Steve C]

Its most likely that the ballistics quoted on the Federal website was taken from a 4" or longer barrel. Typically that's the length used by most ammo manufactures for their tests of handgun ammo. Often they will list the barrel length of the test gun but I don't find it on the the Website. Loss of a approximately 70 fps for each inch of barrel length isn't an unusual amount.

This article A Pair of .32 Magnums: S&W's New Models 431 and 432 J-Frames regarding your model pistol is on Gunblast and if you look down the page there's a chart with some of the ammo they tested and its velocity. Federal 95gr FPL measured an average velocity of 859 fps for 5 rounds which is close enough to your measured velocity to confirm that it is likely a correct reading. There are many variable in velocity readings and different guns even of the same model will often shoot the same ammo at quite different velocities. Since you have 2 pistols of the same model try shooting some ammo out of both and compare your results. Usually one gun will consistently shoot faster than the other.

 

[OKFC05]

A few hints:

When you list the data, also list the number of shots fired, as that makes a difference, particularly in the validity of the SD. 10 is a good number to start with, and more if you suspect the results.

Be sure to stay back enough that the "shadow" from the muzzle blast does not register on the screens and give a false reading.

When you list the data, leave off the digits past the decimal, as they are not significant. If you measure the same load and gun tomorrow, the results will not match exactly, but should be close.

Don't be surprised if your data for your gun differ from factory data, particularly if you do not match the test barrel length. The more you use the chrono, the more this will become routine. I have two "identical" 4" revolvers, but one is consistently 30fps faster than the other.

 

[Jellybean]

1- The velocity is WAY down from the "rated" velocity Federal publishes (887 vs. 1120).
Is that just due to firing it out of a 2" barrel?
Or...something else going on?

2- Is the "spread" and s.d. about what you guys are used to seeing? Or... not?
JamesD

You will get some velocity loss shooting from a shorter barrel, but getting close to "advertised" velocities is a fantasy in most cases. I actually believe they test them in an oven to get the velocities some of them claim.

Sometimes you will get very small spreads and deviations while others may be pretty unbelievable. It sounds like everything is working normal.

 

[JamesD]

Its most likely that the ballistics quoted on the Federal website was taken from a 4" or longer barrel. Typically that's the length used by most ammo manufactures for their tests of handgun ammo. Often they will list the barrel length of the test gun but I don't find it on the the Website. Loss of a approximately 70 fps for each inch of barrel length isn't an unusual amount.

IF Federal tested on a 5" barrel, 887+210=1097, which would be dead on. (I know, "if"...but just speculating.)

This article A Pair of .32 Magnums: S&W's New Models 431 and 432 J-Frames regarding your model pistol is on Gunblast and if you look down the page there's a chart with some of the ammo they tested and its velocity. Federal 95gr FPL measured an average velocity of 859 fps for 5 rounds which is close enough to your measured velocity to confirm that it is likely a correct reading. There are many variable in velocity readings and different guns even of the same model will often shoot the same ammo at quite different velocities.

Actually, one of his rounds was an 85 gr, Black Hills jhp which is (on paper) identical to my Federal round. His avg. vel. was 870 fps (to my 887). Pretty dang close. Thanks for this link!

Since you have 2 pistols of the same model try shooting some ammo out of both and compare your results. Usually one gun will consistently shoot faster than the other.

I'm gonna DO THAT!

Thanks for all of this Steve.

A few hints:

When you list the data, also list the number of shots fired, as that makes a difference, particularly in the validity of the SD. 10 is a good number to start with, and more if you suspect the results.

Be sure to stay back enough that the "shadow" from the muzzle blast does not register on the screens and give a false reading.

When you list the data, leave off the digits past the decimal, as they are not significant.

Thanks for the "Hints" OK. I was hep to the shadow of the muzzle blast. Will surely list the # of shots in the string if I post such data again, and leave off the tenths and hundredths (I see what you mean, sorta silly). See, I'm learnin'.

Thanks.

getting close to "advertised" velocities is a fantasy in most cases.

It sounds like everything is working normal.

Thanks, man.

___________


And... thanks again, everybody.


JamesD

 

[Alk8944]

James,

A "chronometer" is an extremely accurate time keeping device, in short a clock.

What you are discussing is a chronograph. This is a device which contains a high speed timing device triggered by the screens which read the passage of a bullet and measure the time it takes to pass between the two measuring points and converts this to speed. It contains a clock, but it is not a clock.

So far as velocities are concerned even the factories can't get it consistent. The Federal 85 JHP load has been published at 1100 and 1120 and possibly other speeds in the same range over the years. I don't have a 2", if I want a snubby it is a .38 Spl at least. I do have two .32 H&R revolvers, a 4" Ruger SP-101 and a 4 1/8" (actual listed length) Model 631. I have chronographed both Federal factory loads on several occasions and this is what I got, average velocity only shown.

85 gr JHP: Then published @ 1120 FPS

Test #1, 1074 FPS In Ruger SP-101, temp ca, 65 degrees.

Test #2, 927 FPS In Ruger SP-101, temp ca. 50 degrees.

Test #3, 946 FPS In S&W 631, temp ca. 50 degrees.

Test #4, 998 FPS In S&W 631, temp ca. 50 degrees. **

Average of tests 986 FPS, 114 FPS less than published velocity. Total rounds read, 47.

95 gr Lead SWC: Then published velocity 1030 FPS

Test #1, 944 FPS in Ruger, temp ca. 65 degrees.

Test #2, 905 FPS in Ruger, temp ca. 50 degrees.

Test #3, 894 FPS in S&W 631, temp ca. 50 degrees.

Test #4, 962 FPS in S&W 631, temp ca. 50 degrees. **

Average of tests, 926 FPS, 104 FPS less than published velocity. 59 total rounds read.

** After barrel was set back to reduce B-C gap to minimum consistent with function.

The point is to show you the differences in velocities that can be seen due to different guns and testing temperatures compared to factory advertised velocity information. Note that both averages are slightly more than 100 FPS slower than published velocities. It is hard to assign any significance to this as we have no idea the test conditions, barrel length, barrel type (solid, vented, revolver), temperature, air pressure, relative humidity, etc.

With your 1 7/8" barrel compared to my two basically 4" guns, you can expect to see an additional loss of 50-100 FPS due to barrel length, B-C gap, internal barrel and chamber dimensions, temperature, etc. What you show is 99 FPS below my average and 30 FPS lower than my slowest sample with the same ammunition. It looks like your velocity is right where I would expect it to be with that barrel length.

You don't say how many rounds you fired. To even begin to have a statistically significant sample a shot string needs to contain at least 20 rounds. The more shots in the sample the more the ES and SD indicate. Many people fire 5 rounds and think the result represents at least their average velocity for the load, it doesn't. Note the samples I show are from 12 to 15 rounds per string, after all, factory ammunition isn't cheap! My only purpose was to determine an approximation of average velocity for the factory loads in my guns.

Think of it this way. If your sample is 2 shots and the velocities are 900 and 1000 FPS your mean will be 950, ES 100 and SD ca 40. If the sample is 20 rounds, High & Low the same, the ES would still be 100, Mean approximately 950, but the SD less than 10. Likewise, same sample size of 2, velocities 995 and 1000. Mean will be 997.5, ES 5, SD about 2. Can you depend on the next 100 rounds falling between 995 and 1000, not likely. This is why the larger the sample the better. Averages of several short strings added and averaged together at a later time mean nothing either due to variation in conditions on different days.

I hope this makes sense to you.

 

[JamesD]

Thanks, alk8944.

In my brain I knew I was using a chronograph, but somehow it came out through my typin' fingers as chronometer. But regardless I HATE poor scholarship! Thanks for the correction.

Thanks for showing me how you list your results, with temperature and all.

And all your discussion at the end was understood and appreciated.

And, re: the brief discourse on sample size, s.d., etc., you say, "I hope this makes sense to you"... yep. I had a modest amount of statistics in grad school, and though it's been 40 years since then, there's still some of it firing around in a few synapses, and I get exactly what you're saying.

You and everybody else have been most friendly and helpful.
Thanks a bunch.

I'll get out again soon with my chronograph and do some longer strings, compare my two 431 P.D.s to each other, and also my new/old 1950 Colt Commander and put all y'alls advice and comments to work.

Thanks again.

JamesD

 

[Skip Sackett]

You aren't the first to notice that factory ammo doesn't always reach the advertised velocity. The venerable Speer #8 manual has two whole pages dedicated to this phenomenon!

Not only do the ammo folks tend to be a bit "optimistic" about their achieved speed, powder manufacturers do too at times!

I have shot TONS of 45ACP through 1911's and M625JM (4" barrel) and I can tell you this from experience, the barrel/forcing cone gap plays no part in velocity. In fact, across my chronograph, the 4" gun matches the 5" almost to the tenth in fps.

All of that being said, it is the most practical tool for the handloader. You cannot tell pressure with one BUT it will tell you if you are matching velocity.

At any rate, here is a link to the Speer #8 page on the issue. Kind of hard to read but you will notice they had some real different results between published data and actual data.

FWIW

BBHFarm Gallery :: Speer #8, Speer Inc, 1970 :: abf

 

[Alk8944]

JamesD,

Glad you found this useful. Just one other comment about the factory loads I fired. These were from four separate boxes of ammunition for each load purchased at different times and likely of several manufacturers lots each. This introduces a totally different set of variables between the separate test strings listed, so temperature and gun weren't the only variable.

Basically these tests were to develop some useful information while obtaining cases to load. At the time shooting Federal factory loads was the only way to obtain brass for .32 H&R. If you are going to load for the .32 H&R I would suggest Star-Line brass if you expect to warm up your loads, Federal is too soft and doesn't hold up well.

If you are interested I know a dealer in Salt Lake City that has both a 4" Sp-101 and a 4" S&W 631 in the used case. The 631 is $650 with the box, the SP-101 is $325 I believe. They were still there 3 hours ago. If you are interested send a PM and I will give you contact information.

 

[JamesD]

Alk8944,

Working sorta backwards through your post...

If you are interested I know a dealer in Salt Lake City that has both a 4" Sp-101 and a 4" S&W 631 in the used case. The 631 is $650 with the box, the SP-101 is $325 I believe. They were still there 3 hours ago. If you are interested send a PM and I will give you contact information.

The way this story unfolded, I got a pair of old Smith j-frames passed down to me, one that was my father's and one my mother's.

Basically these tests were to develop some useful information while obtaining cases to load. At the time shooting Federal factory loads was the only way to obtain brass for .32 H&R. If you are going to load for the .32 H&R I would suggest Star-Line brass if you expect to warm up your loads, Federal is too soft and doesn't hold up well.[/QUOTE]

And indeed I am currently shooting the Federal #C32HRB round and saving the brass to reload. (...or more precisely, to hopefully find someone to send them to for reloading, as I don't reload myself)
Which brings up two questions I could maybe ask:

1) if this is going to be used in a 2" gun, I was under the impression that it is really not terribly productive to hot up the load. Am I correct about this?

2) If I'm going to be staying with standard loads, is the Federal brass OK to reload for this? Keep saving them?

Much obliged for any comments.

JamesD

 

[rodell]

It isn't terribly productive to soup up the loads. You need more barrel to get much out of it. You might get some impressive flash, though.

That brass is fine to reload. However, try to find someone who will teach you and let you load on their equipment. As a general rule, don't buy reloads unless you are VERY sure of the reloader.

Bob

 

[WR Moore]

Something I didn't see mentioned in any previous posts are:
1. Distance from the muzzle to the first screen (actually should be to the middle of the sensor set). About 15 feet is average to avoid various issues. Please note the factories use a formula to convert this reading to muzzle velocity, so you're going to show "slow" without the conversion factor.

2. The factories use fixtures to hold the measuring units and the weapon. This insures that the bullet passes over the "clocks" at precisely the same height, dead parallel to the sensors and on the shortest possible path-that is straight through. Deviations from this will affect your readings and result in lower velocities.

3. Barrel length: SAAMI sets the test barrel length at whatever the catridge developer specifies. Just as they get to specifiy the rest of the technical package including pressures, overall length, etc. The weapons manufacturers have little to say about it unless they developed the cartridge.

 

[toofless]

Chronograph

While discussing Chrono's-- Does anyone have an idea on how to avoid shooting the screens? I am a three time loser on this

 

[38-44HD45]

To avoid shooting chrono skyscreens (or the box itself, with some) it helps to place a target downrange of the screens, so that you actually have an aiming point, rather than just bracketing the sights between the uprights holding the sunshades. Also, work on trigger control...

To the OP: Welcome to the world of chronography! It is a real education. At my age, I've gotten where I almost enjoy clocking bullets as much as actually shooting targets or critters.

 

[Steve C]

Does anyone have an idea on how to avoid shooting the screens?

The flip answer is aim above he screens.

If you don't know where your bullet goes in relation to your point of aim, place a target at the same distance as the chrono with a small aiming point and see where the bullet hits. Adjust your elevation and windage as needed. Hitting the area above the screens at 15' (5yds) should be a non issue with handguns, with a scoped rifle the scope height can put the point of impact low.

 

[Alk8944]

Something I didn't see mentioned in any previous posts are:
1. Distance from the muzzle to the first screen (actually should be to the middle of the sensor set). About 15 feet is average to avoid various issues. Please note the factories use a formula to convert this reading to muzzle velocity, so you're going to show "slow" without the conversion factor.

2. The factories use fixtures to hold the measuring units and the weapon. This insures that the bullet passes over the "clocks" at precisely the same height, dead parallel to the sensors and on the shortest possible path-that is straight through. Deviations from this will affect your readings and result in lower velocities.

3. Barrel length: SAAMI sets the test barrel length at whatever the catridge developer specifies. Just as they get to specifiy the rest of the technical package including pressures, overall length, etc. The weapons manufacturers have little to say about it unless they developed the cartridge.

These questions are often posed. They are all red herrings as they are either untrue or of so little impact to results that they need not be considered. Let's take them in order.

1) Distance to screens and velocity correction to the muzzle. Anyone who has an exterior ballistics program can correct velocity from instrumental to muzzle velocity. The only factors that affect the magnitude of this correction are the average distance to the screens and Ballistic Coefficient of the bullet being fired. Without getting too deep into all variables, like change in BC with velocity, the average correction factor for a revolver and screen distance of 10-15 feet from muzzle is 3 FPS. This is why I never mention screen distance. The difference between 10 and 15 feet is approximately 1 FPS! If you want to get anal over 1 FPS go ahead, or 3 for that matter, but to me it isn't that important.

2) Errors due to angularity. For this to be a factor would require shooting at deliberately different angles, not a few minutes or seconds of angle incidental difference. At usual start to stop screen spacing of 1-2 feet it would be difficult to assign a variation of even 1% to average velocity through this error. At an average 1000 FPS the most variation this would introduce would therefore be no more than 10 FPS, again so small a variation that statistically it is insignificant. Most revolver loads will show a higher Standard Deviation than this!

3) This is simply not true. SAAMI in cooperation with firearms and ammunition manufacturers publishes what have been universally decided upon by the industry as a whole as MAP (Maximum Average Pressure) standards for various cartridges. This, and standard barrel dimensions are the only factors which are specified by SAAMI. Velocities or test procedures are not specified by SAAMI. Barrel length, barrel type, distance to screens, bore and chamber dimensions, and everything else which would affect test results are strictly at the discretion of the ammunition manufacturer doing the testing. Even the method of pressure testing, crusher, piezo guage or strain guage, is also at the discretion of the manufacturer.

The factor having the greatest influence on velocity results is rarely mentioned, and that is temperature. A velocity variation of only 10 degrees Fahrenheit can cause a variation of average velocity of as much as 50 FPS. Since the operative factor here is ammunition temperature at moment of firing is extremely difficult to measure the convention is to use ambient air temperature as the noted test temperature. In all actuality ammunition temperature can vary widely from air temperature. Has it been exposed to the Sun, is there a breeze blowing, how fast? Is the gun hot, has the ammunition "soaked" in the chamber and been heated by the gun, how much?

Do you see how silly worrying about 2-3 FPS due to screen spacing, incidental angularity, etc are?

All we can ever be testing for when chronographing, handloads or factory ammunition, is what approximate velocity can I expect to get from this ammunition, on this day, under these conditions, in this gun that I fired the test string in. The real revelation is to shoot the same batch of ammunition in several guns during the same shooting session. It is really interesting to see the same ammunition give, say, an average velocity of 850 FPS in a 6 1/2" revolver and 925 FPS in another, same brand and model, that has a 4" barrel! Then you will really see how impossible it is to expect anything like published velocity in any gun. Sometimes you will even see ammunition run at higher than published velocity in a particular gun!

 

[Skip Sackett]

You can put a piece of tape on the rod. I have heard that that helps. On my new chronograph, it has rod extensions with brass couplings. I use that most of the time when shooting a firearm with a scope. !!Stay above that line!!

I had son #2 test his 30/06 hunting rifle once, here are the results"

Needless to say, they won't stand up to a 165gr bullet going just under 2800fps!

He was a real sport. After we got done shooting that day, he went right to the store and bought another one! Slightly better model too!

Remember though, on a scoped gun, the barrel is as much as 2" lower than where you are looking!

 

[H Richard]

Yes, put a mark on the sky screen uprights. I just "barely nicked" my original chrony with a 240 gr JHP from a Mod 29, well, you can guess the result. Chrony does allow a decent trade in value (regardless of condition) of an old Chrony on a new Chrony. I now have the Beta Chrony. Having the readout on the bench with you is much more convenient than 12 ft. out.

 

[JamesD]

Oops! I've been away for a couple of weeks!

Just finished catching up on this thread.

Thanks everyone, in particular Alk8944 for continuing input.

This is such a nice forum. So many knowledgeable, helpful, dedicated and NICE people here!

Thanks again!

JamesD

P.S. to 38-44HD45

To the OP: Welcome to the world of chronography! It is a real education. At my age, I've gotten where I almost enjoy clocking bullets as much as actually shooting targets or critters.

Thanks for the Welcome, and you know, I really enjoyed my first Chrony-day at the range. You shoot enough paper, or steel plates, over and over and over. Starts to get a little "routine" maybe. This was something new and sort of geek/tech fun. I enjoyed it!