How Important is a Chronograph to safe reloading?

[Wildalaska]

Now can I assume if your chrono is showing a higher velocity than published there is a chance you are too high on the pressure?

Chance...yes.

WildbutsomanyotherthingstoconsiderAlaska ™©2002-10

[mehavey]

Quote:
Now can I assume if your chrono is showing a higher velocity than published there is a chance you are too high on the pressure?

Chance...yes.

And that's where the Internal Ballistics program comes in.

By knowing the actual velocity as compared to the predicted velocity (for which internal ballistics program also associates a pressure curve), you can get a pretty good handle of the actual pressure as well.

[Nnobby45]

Now can I assume if your chrono is showing a higher velocity than published there is a chance you are too high on the pressure?

Not necessarily, but certainly possible. Remember, individual rifle pressures vary in that regard. Only if you knew you were at max would an increase in velocity (and of course pressure) indicate you've exceeded SAAMI specs.

However, if the handloader doesn't exceed the recommended powder charge AND doesn't exceed recommended max velocities, then that's an excellent safe loading practice. You have to allow, however, for different bbl. lengths. Figure 60fps per inch in velocity loss/gain.

Once you established your load, the chrono is good for keeping you consistent and determining velocity/pressure changes when using different components. Case and primer changes, for example. Bullet changes, also---even if you go to a different bullet of the same weight. The chrono will note vel/pressure changes and you'll learn a lot.

For example, I know-- from using my chrono--, that Win Mag. lg. rifle primers deliver about 50 fps more velocity than standard primers, and I know there isn't enough difference to worry about between Rem. and Win standard primers.

If you go to a different powder, then you have to start all over again, since velocities may be the same with two different types of powder while pressures vary. To understand that, study your manual and you'll see that some powders produce higher/lower velocities with less pressure than others.

As a general rule: Choose a powder that produces the highest velocities, since they're obviously efficient. Choose from several that meet that criteria. You don't have to pick the highest one. It may not be the one for best accuracy.

On the other hand, all powders listed in the manual are suitable to use. Just follow the recipe.

To get a good sense of a rifles accuracy potential, I might suggest the Nosler Ballistic Tip to experiment around with. Get those shooting well, and then try other bullets.

Working up loads is fun and for many, a persuit in itself. It's probably true that more rifles have been worn out in load development and experimenting than from hunting or many types of target shooting.

[Clark]

In strong rifles I don't care what the pressure is, I only care about the effect of pressure on the brass. For that information, I do not consult the chronograph, the primer, the strain gauge, the load book, Quickload, nor an astrology chart. For informaion on the effect of pressure on the brass, I look at the brass.

This reminds me of an old fashioned definition of insanity, taking leave of one's senses. In this case it would be taking leave of one's brass and looking at the chronograph.

[mehavey]

That "strong" rifle's weak link is that soft/malleable brass case. When it fails... you have a gas, brass, and maybe steel moving at high speed toward your face, hands, arms, and eyes.

What effect on the brass shows up in one -- (the first) -- shot? With today's components, the traditional brass/primer indicators are notoriously inconsistant (if not outright misleading). Unfortunately they mislead folks to think thay are still "safe."

Unless the primer pockets are so grossly enlarged as to cause the primers to fall out, and/or case head visibly/assymetrically swelled, and or the case base shows where bolt rotation as scraped brass off as it flowed into the bolt face depressions -- and on that first shot -- one is flying blind.

And if/when they do show up, the shooter is waaaay past safe pressures.

[Clark]

mehavey That "strong" rifle's weak link is that soft/malleable brass case. When it fails... you have a gas, brass, and maybe steel moving at high speed toward your face, hands, arms, and eyes.

What effect on the brass shows up in one -- (the first) -- shot? With today's components, the traditional brass/primer indicators are notoriously inconsistant (if not outright misleading). Unfortunately they mislead folks to think thay are still "safe."

Unless the primer pockets are so grossly enlarged as to cause the primers to fall out, and/or case head visibly/assymetrically swelled, and or the case base shows where bolt rotation as scraped brass off as it flowed into the bolt face depressions -- and on that first shot -- one is flying blind.

And if/when they do show up, the shooter is waaaay past safe pressures.

I find that measuring any changes around the extractor groove is a better pressure indicator and precursor for loose primer pocket than either waiting for the primer to fall out or measuring the primer pocket with pin gauges.
That is because the spent primers can stay in there like hanging chads, and the expansion is often not symmetrical. The non symmetrical expansion can be found by turning the calipers relative to the outside diameter of the extractor groove, but round pin gauges are blocked if any part of the primer pocket maintains the original diameter. When I developed this system, ~ 5 years ago, it was suggested that I find "D" shaped pin gauges, but I have not done that.
The extractor bevel is aligned with the dial caliper jaw bevel. That means the dial is pointed toward the case mouth.
The force of the jaws on the extractor groove is kept constant, and the case is rotated.
A min and a max are noted.
The cartridge is fired and the measurement is repeated.
If any change in the brass is detected, that is the end of the work up and the powder charge is reduced from there by a safety margin for useful loads.

Typically, it is something like:
7) 49 gr. extractor groove expands .0000"
8) 50 gr. extractor groove expands .0020"
9) 51 gr. extractor groove expands .0020"
10) 52 gr. extractor groove expands .0110", primer fell out

One only needs .001" resolution to find the change.
The max practical load is going to be 47 or 48 gr for hunting big game long range, and 46 gr for zillions of shots at varmints.
Vernon Speer said the margin should be 6% powder charge from the threshold of brass change back in 1956.

The amazing thing is the consistency.
Different brand of brass, primer, bullet, rifle, reloading die, reloading press, and powder scale.
Different day at the range and different temperature.
Same powder but different lot #, same bullet weight and bullet length, same over all cartridge length and not touching the lands.
The consistency is typically within 1% for the threshold of extractor groove diameter change.
That says something about what we are getting when we pay for powder to be blended into canister powder.
If I do this with bulk powders, things turn out very differently.

[mehavey]

I did a Google search on "extractor groove expansion pressure" and (surprise) ran into your SnipersHide post on the same subject.

In that longer article you listed some data (many thanks for keeping good notes) that I found interesting:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Pacific .308 Win reamer, VZ24 trued action, A&B fluted stainless 24" F54 barrel, H335, CCI200 primer, 2.9" OAL, Speer 168 gr. HPBT Gold Match, brass: Win308Win:

1- 10 order left through right

0) 42 gr. QL= 2565 fps & 46 kpsi, 0% overload, did not load 42 gr.
1) 43 gr. QL= 2618 fps & 49 kpsi, 2% overload, ok
2) 44 gr. QL= 2670 fps & 52 kpsi, 5% overload, cratered primer this and higher
3) 45 gr. QL= 2722 fps & 56 kpsi, 7% overload
4) 46 gr. QL= 2774 fps & 60 kpsi, 10% overload
5) 47 gr. QL= 2825 fps & 64 kpsi, 12% overload
6) 48 gr. QL= 2875 fps & 68 kpsi, 14% overload, mark on brass from bolt face extractor this and higher,
7) 49 gr. QL= 2925 fps & 73 kpsi, 17% overload
8) 50 gr. QL= 2974 fps & 78 kpsi, 19% overload, extractor cut on brass expands .0020"
9) 51 gr. QL= 3024 fps & 84 kpsi, 21% overload, extractor cut on brass expands .0020"
10) 52 gr. QL= 3073 fps & 90 kpsi, 24% overload, extractor cut on brass expands .0110", primer fell out,
~~~~~~~~~~~~~~~~~~~~~~~

I note that primer "flatness" used to be my first incipient pressure sign -- no longer useful as its "flatness" is dramatically affected by how closely headspace is controlled; and today's primers tend to be built of sterner stuff anyway. (I do remember some really flattened primers from my earlier/1970 days wherein knowing what I know today now terrify me)

Primer cratering is also as much/more a function of loose(r) firing pin fit to the bolt's firing pin hole -- the greater the clearance for the primer to get a good run in set-back (and the softer the cup) the lower the pressure at which cup material flows back into/around the pin. So I gave up on that as consistant/sensitive sign. (Note that cratering appeared within perfectly acceptable commercially-loaded pressures [52 ksi] above.)

Brass strength failure is (and remains) the next best indicator and sticky bolt lift used to be a warning that the bolt was having to deal with shearing through extruded brass as it rotated -- You noted case head flow/shear into the bolt's extractor cut-out first became visible at almost 70 ksi. At that point the shooter is way past the safe zone (and chewing up his brass to boot).

If I'd had a chronograph during this run-up, I could have stopped between just short of/at ~2700 ft/sec average velocity and been pretty sure I was working at/under max pressure. Without it, I'm having to load up until brass flowed into the extractor to calibrate -- bad juju.

Also, with the chrograph I'm able to go from one can of powder/lot# to the next (over the years) as well as from one brand/lot# of cases to the next, and quickly reestablish my performance-based loading standards to those same ballistics -- just like the military arsenals do.

But without the chronograph (being a starving church mouse in my salad days), I used to measure case head (as opposed to extractor groove) expansion in a last-ditch indicator of incipient brass overload. Then I read this article:

http://www.shootingsoftware.com/ftp/...%2019%2004.pdf

and its bottom line....

"The statistics leave no doubt that pressure ring diameter is
correlated with peak PSI. The problem is, it’s not very well
correlated. It explains only 42.6% of the variation, with
other, unknown factors explaining the rest—over half.
Another way of saying this is that the model contains more
random noise than it does information...."

Aaaaahhh Shucks. Was nothing sacred?

[Clark]

So the bottom line is that I have a repeatable process, and with it the loads in load books can be evaluated for the percentage powder charge they are below brass change threshold in an 1889 7.65x53mm Mauser case head [30-06, 243, etc] made with a large Boxer primer.

You will find that some load books are all over the map, like Hodgdon or Speer, but some, like Sierra, are consistent in the powder charge safety margin.

It also works for 1950 222Rem case heads [223, 204, etc] made with small Boxer primer pockets.

It does not work for 6mmBR or 30-30 case heads, which have stronger primer pockets than the pierced primer level.

[Nnobby45]

This reminds me of an old fashioned definition of insanity, taking leave of one's senses. In this case it would be taking leave of one's brass and looking at the chronograph.

Who suggested doing that? I've been trying, without much success to impress upon the fact that the chrono is a supplement. As in, your case for example, look at your brass and see a little high pressure, then back off until the load is safe, then chrono it so you know where the velocity needs to be. Then, you can easily return to that pressure (with the same powder and components) level because you've monitored the velocity and know right where you are.



Don't care about pressure? Ah jeez.

[SL1]

Remember that the loads in manuals were pressure-tested in one barrel (a SAAMI-spec chamber in a pressure-test barrel), but then velocity tested in a different barrel (some common commercial gun which most probably has a somewhat larger chamber).

It would be nice to know what the velocities are from the pressure-test barrel, but we usually don't get that. The published velocities from the commercial gun may be close to the velocities from the test barrel, or they may be substantially lower. Presumably, if the velocities are lower, then so are the pressures. That means that the data in most manuals is a mixture of "apples and oranges."

So, WildAlaska is correct. If your chronograph is showing higher velocities than the manual showes for the same load, then you MIGHT be getting higher pressures than their maximum load did in their pressure-test barrel, OR, you may still be below that pressure, but above the "unpublished" pressure in the commercial barrel that was used to produce the published velocity. There are just too many unspecified variables (powder lot, case capacity, etc.) to be able to tell for sure.

SL1

[Clark]

If my goal is to find the upper limit of brass life from loose primer pockets, then I think measuring the extractor groove is better than getting the primer to fall out or measuring the primer pocket or feeling the effort to remove the old primer or the effort to insert a new primer.

Chronograph data is not even an "also ran".
Primer appearance is not even an "also ran".
Denton Bramwell type strain gauge measurements is not even an "also ran".

One curious thing is that Scott Sweet's Von Misses calculations on case head failure is very close to the Quickload calculation of pressure where the threshold is found.

I find the .223 gives up the ghost at 86 kpsi +/- 7.5% QL
I find that the 308/243 gives up the ghost at 75 kpsi +/- 3.5% QL
SS predicts .223 gives up the ghost at 86.4 kpsi +/- 7%
SS predicts 308/243 gives up the ghost at 77 kpsi +/- 7%
Pretty good correlation between that engineer's calculations and Quickoad predictions of my tests, huh?

[GP100man]

Nessesary no , but a cheap peace of mind !!!

I loaded for 25yrs with out 1 & when I did get 1 it was eye openin to say the least!!

[Nnobby45]

I loaded for 25yrs with out 1 & when I did get 1 it was eye openin to say the least!!
__________________

That's what I'm talkin' 'bout!

[teeroux]

Reloading without a chronograph is like driving a vehicle without a speedometer.

You joke but I have gotten around just fine with 2 vehicles that had no speedometer.

I also get by just fine without a chronograph but I do want to get one.

[Ike666]

As someone else pointed out, for safety its kind of after the fact that the chorno gives you any useful information. If you're working up some loads and checking them one step at a time it might keep you from going too far.

Years ago I had a Chrony F1. Simple, basic, but I found it very useful developing some .45 ACP and 9mm loads. Then I stored it and just recently took it out to test some .357 SIG loads. It didn't work anymore - the display just flashed. I did notice that somewhere along the trail I had put a 9mm through the rear screen (but not the front - talk about straight shooting).

When it didn't work I replaced it with a ProChrono which I first took to the range yesterday. It was invaluable to my purposes - but not so much as a safety tool. I was watching the velocities on one load as I approached max thinking I might have to stop. The final result was the near max load was okay, but I'd be real hesitant to push the round any further. No need to do so b/c cooler loads got the job done. I wouldn't have known this without the chrony. So, to the extent that it kept me from following the "bigger is better" path it did serve a safety function.

Necessary, no. A real useful tool - most definitely.

[Nnobby45]

You joke but I have gotten around just fine with 2 vehicles that had no speedometer.

OK, how far do you want to take this argument? In Biblical times people walked where they went or rode on an ass--and got along fine.

A few decades back, we all got where we wanted to go in a two wheel drive pickup. If it snowed, we put our chains on. We got around just fine.

We had B&W tv's for a long time. Look at all the tv we watched and never worried about color.

My grandmother used to wash clothes with an old ringer tub style washing machine. It worked. Didn't have pampers then, diapers had to be washed. Worked just fine.

So did VHS and Beta.

People even handloaded and got good at it without a chrono.

Some even used loose primer pockets and flattened primers to determine that their loads were above max. Some even appear to still be doing it.

[Clark]

How did people get along before the Ouija board?

The Oracle at Delphi?

[Farmland]

After reading everything and some other sources I am going to get one. How is the F-1 CHRONY? It is pretty cheap or should I buy a better one?

[Ike666]

I'm certainly biased b/c I just bought a new ProChronograph. But I also own an F1 Chrony - my first chronograph. It worked well for what it was but I was younger then and I'm so much older now. I could see the display clearly from 10-15 feet away then - couldn't do that now.

I stored the F1 for about 6 years and when I took it out and put a battery back in it the display just flashed and it wouldn't work. That's not really a complaint about the chronograph and it still might be fixable - I'm going to write Chrony.


I like the new one b/c of the computer interface. I bring along my MacBook (running in Windows) and it has a nice large shot display plus a window for the accumulated statistics for the string. I can also save each string out as a CSV file and then easily read it into Excel for further analysis. Its great for working up loads.

[Edward429451]

I reloaded for at least 20 years without a chrony. The first thing I wanted to do is chrono my good loads. It was very satisfying to see good numbers fall out for my pet loads!

I have learned so much from the chrono over time that I will call it important even though it has been shown that it is not crucial. I do want a speedometer in my car though! There is a need to be able to fine tune the speed of my vehicle, being the grey man to the police and thier ticketbooks!

Seriously, you guys seem to be in two camps. We don't need it, and we think it's essential. Don't miss the point, chronos are a supplement to knowledge and data and should be embraced. I didn't stop looking at my brass when I got my chrony.

I'm not sure if I buy it that good loads don't have to have low SD. I will buy it that adequete loads may not have to have low SD, but these benchrest guys and moa freaks (sorry!) that make these good one hole loads and all that...I don't think they accomplish it without low SD & low ES. The consistency has to be there or they could not shoot <moa at the distances they do. Show me a load with a 200 fps es that's moa and repeatable!

That's the usefulness of a chrony. Poor loads can be abandoned sooner powder saved ;-)

[Nnobby45]

After reading everything and some other sources I am going to get one. How is the F-1 CHRONY? It is pretty cheap or should I buy a better one?

Get the ProChrono from Competitioin Electronics. Besides making a good chrono, their customer svc. is very good.

[farmerboy]

That last comment, I believe was #71 is what its all about. We can all agree or disagree on different things but it doesnt really matter, when one of us really needs help just about everyone on here is willing to help out a brother in need. WAY TO GO!!!!