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crabo
11-19-2010, 12:12 AM
A friend of mine had his chrono set up, so I ran some of my 45/70 guide gun and ammo through it.

5 shots
42 grains of 3031, WLR primer, Starline brass, sized .460, wd wws, c red lube, the boolit was the 460360 group buy. (360 grains)

1479 fps
1517 fps
1465 fps
1515 fps
1424 fps

High 1517
Low 1424
Total deviation 93
Mean 1480
$ 38 (standard deviation?)

It seems like this is a pretty wild velocity swing. However when I shot my last four boolits for accuracy at 50 yards, I am fairly happy with the results.

I need to shoot this load at 100 yards now and see what it does, but what do I do with the info I have? Do I try to work up a load that has less deviation, or just shoot a couple hundred of them as the barrel breaks in, and then revisit?

x101airborne
11-19-2010, 12:59 AM
ummm..... rain on that chrony. If you get good groups / performance, why bother? I started to sweat seeing the same info from my chrony on a 44 mag, 240 gr swc. Seems like you got a pretty good start for the guide gun, so shoot at 100 and tweak the load. Once you have done everything you can to gain even 1/10" accuracy, check your notes, load some fresh ammo, then shoot over the chrony. in short, USE THE FORCE, LUKE. listen to the weapon, verify results with the chrony.

Larry Gibson
11-19-2010, 01:46 AM
Frankly, one 5 shot string and a 4 shot group at 50 yards doesn't tell you a lot. There are indicators there, some good and some not so good. What you're calling "total deviation" is usually refered to a "ES" (Extreme Spread). You are correct that a 93 fps for a 5 shot ES is a "pretty wild velocity swing". I'd suggest using a 1 gr dacron filler with that load. It will up the psi slightly and the velocity but your load is well within safe limits for it. It should reduce the ES by a considerable amount. If you want to stay at that velocity then drop the charge 1-2 gr and test again.

Testing at 100 yards is always preferable to 50 yards. Variables in the load that affect accuracy will be much more apparent than at 50 yards, especially so since you are using a scope. Using the chronograph in conjunction with shooting groups is always more effective and informative than doing both seperately.

Larry Gibson

AZ-Stew
11-19-2010, 11:59 AM
When I was working up loads for heavy match bullets in my AR, I came across one load that chrono'ed at a SD of 2fps. The groups from it weren't as tight as a different charge of the same powder that produced a SD of 10fps. While both of those SDs are low, they are not representative of most loads you'll chrono. Most will have greater SDs. Nothing wrong with that as long as the bullets all go to the same spot at the distance you intend to use them. Someone shooting at very long distances may prefer to give up a little precision in his load to achieve a lower SD to avoid vertical stringing at long range.

Regards,

Stew

montana_charlie
11-19-2010, 02:08 PM
The Total Deviation (ES) of 93 is pretty lousy, and the Standard Deviation of 38 is nothing to brag about. But those variations in velocity won't show any effect on the target until you start shooting at a distance where velocity actually matters.
50 yards isn't it.
CM

Larry Gibson
11-19-2010, 02:11 PM
I concur with A-Z that one should not "chase an SD". This is because when both the SD and/or ES are high (as in crabo's load) then something is not very good about the load. It is important to observe that the SD and ES are both proportional and one or both are not too high. We also must remember that it is unlikely that we will get the same average velocity if we shoot several strings of the same ammo in the same rifle one after another. The averages will be different as will the SD and ES for each string. However, they should remain close to each other (within a few fps). If they do not then there is something wrong.

We must also consider the validity of the information based on the number of shots based on statistical valid sampling. If we chronograph just one shot we can only say what the velocity of that one shot was. If we chronograph 3 shots it gives us an indicator of the possible average velocity range and sufficient cases to examine for any potential pressure signs. If we chronograph 5 shots it gives us a pretty good idea of the probable average velocity of the load and the SD and ES. Most ballisticians concur it takes a minimum of 7 shots (most test with 10 shot strings) to get a statistically valid sample to say with any degree of certainty what the average velocity is or how uniform the load is based on SD and/or ES. All this given an accurate setup and use of the chronograph.

As I've stated for a number of years, based on 38+ years of extensive use of a chronograph, that testing for groups also while chronographing is the best method of testing/developing loads. Here again though we must use a sufficient sample size to really get an accurate picture. Back in '75 when I got my 1st Oehler chronograph I thought a 3 shot string was sufficient and started out just chronographing thinking that the most uniform load would be the most accurate. It didn't work out that way mostly because the 3 shots was not giving enough information about the true uniformity of the load. I then went to 5 shot groups because it was what most of the gun writers were doing. I found that was better but some anomalies with some loads still arose. When, in '89 I got an Oehler M35P I found that having the SD and the ES along with the more efficient (I didn't have to turn a dial for each shot, get the time and then convert it to fps using a chart) results was indeed showing me what loads were going to be anomalies. However it still was not 100%.

Only when I had a lengthy talk with Dr. Oehler and did some serious research into internal ballistics did I understand that 5 shots is just not statistically valid. I then went to 7-10 shot test strings mostly using 10 shots. This has proven to be a significant step in eliminating all the anomalies.

Note; when working up a load with a powder or cartridge that I’ve not used before I will most often use 3 shot strings to determine if the load is in the velocity range it should be and if pressures are safe. After that I move to 7 or 10 shot groups to refine the load. On the outset it would appear that this method uses more components than other methods but my experience is I either get a good load quicker with less components of I reject the load quicker. I have found that his method (use of the chronograph with intitial 3 shot then 7 -10 shot refinement groups tested concurrently) actually uses less components getting me satisfactory loads much quicker than the traditional method or the vaunted “Ladder method”.

Test for groups at short range also can give very false indications of accuracy. Of course what constitutes “short range” is relative to the firearm, sights and cartridge being tested. For CF rifles, the subject of this thread, I’ve found that group testing at 50 yards provides little in the way of determining if the load is accurate. For example Somewhat extreme but the results are far enough apart to demonstrate the point) a test I did using cast bullets in the .308W gave the following chronograph results;

Load 1
AV 1912 fps
SD 17
ES 43

Load 2
AV 2498 fps
SD19
ES 44

On the out set it would appear that both loads (10 shot groups) were pretty equal based on internal ballistics (data provided by chronograph). However, there are 3 phases to ballistics; internal, external, and terminal. The group sizes at (again 10 shot groups at each range) 50, 100 and 200 yards were;

Load 1
50; .7”
100; 1.3
200; 2.5”

Load 2
50; 2.55”
100; 4.7”
200; 14.5”

What we see here by collecting the internal data and the terminal data is that something was very wrong with Load 2 in the external phase, i.e. it was accurate. Had we just tested at 50 yards we might have accepted a 2.55” ten shot group as “accurate”. We have all seen such groups (many times with just 3 or 5 shots) accepted that way here on this forum. That load may have been “accurate” enough for deer hunting out to 100 yards and been suitable to use. However, if one is looking for an “accurate” target load then it obviously won’t do. Thus I explain all this to show how the use of the chronograph and shooting for group with a sufficient teat sample is the best way to determine an “accurate” load for your intended use.

Larry Gibson

onondaga
11-19-2010, 02:27 PM
That amount of deviation with a bullet that weight means schnook. You can have worse deviation and still have good group size with that bullet and hunting ranges. A ballistic filler and a consistent heavy crimp will lower the deviation if you really want the numbers. I use BPI Original filler. You have to add the weight of the filler to the bullet for a total projectile weight when calculating load and pressure. I load with filler plus powder to a 105% compressed load and get the numbers with my .458 Win Mag. and reduced loads. This stuff measures well with powder measures or scoops. My source:

http://www.midwayusa.com/viewProduct/?productNumber=695248

Brushing clean and shiny inside the case mouth and brushing mica dry lube in the case mouth also lowers deviation. I use this kit and really like the results:

http://www.midwayusa.com/viewProduct/?productNumber=197010



Gary

Doc Highwall
11-19-2010, 02:56 PM
I agree with Larry on sample size and distance. When I bought my first chronograph I did a lot of research and determined that for rifle 100 yards would be the minimum distance and five shots would be the minimum. My method was to start 10% below what I thought would be my maximum charge and load five rounds and continue in 1% increments of five rounds each and plotting velocity gain and look for a flat spot, along with horizontal and vertical dispersion on the target. I would always find two spots that had smaller horizontal and vertical dispersion one at the low end and one towards the high end. I would then concentrate around the flat spot of velocity gain with larger sample sizes making one change at a time like powder charge and OAL, then start increasing the distance to 200 yards and farther.

felix
11-19-2010, 03:08 PM
That is the way it is supposed to be done, Doc, as in looking for the flat spot with no accuracy difference between several loadings which cover a reasonable powder "weight" swing via a typical volume measuring device. If there is any accuracy discrepancy, then the wrong powder speed is chosen, keeping in mind the ignition difference between various lots can play havoc with very minor weight changes. ... felix

Rocky Raab
11-19-2010, 03:09 PM
Except for the final shot, those aren't bad numbers. Frankly, with most cheap chronographs, that last reading might not even be valid.

If you shoot another four strings of five, and use the ES and SD from all 20, you'd have a better chance of evaluating that load. I wouldn't make any major changes in the load until then.

mpmarty
11-19-2010, 09:46 PM
I think the fifty yard accuracy vs the hundred or two hundred yard is dependent on initial velocity and ballistic coefficient as when a super sonic blt transitions to sub sonic the trajectory is disturbed to some extent and the loss of velocity may be the determining factor in how accurate a round is beyond fifty yards. I don't have a full hundred yard range at home and so I test at fifty and seventy five yards until it's time to go to the range and try at one and two hundred yards to "prove" my loads at distance. I'm sometimes disappointed in the results but that's OK I just go back to my loading bench and change things a bit.

crabo
11-19-2010, 11:22 PM
This helps a lot. I have a chrony, but have never used it. I start at 50 yards because I can shoot inside, rain, or dark, until 9:00pm. After I find good loads at 50, I move outside to the range at 100. The club I belong to, has 50, 100, 200 yard ranges.

I also only shot 5 of each load because of time limits. He had an older Oehler and had it set up about 5 feet from the muzzle. That 45/70 really rocked it and I felt like the concussion was going to blow his lights out. I thought it was too close, but it is his setup.

I want to start using my chrony, so this gives me a good place to start.

ScottJ
11-20-2010, 10:30 AM
The Total Deviation (ES) of 93 is pretty lousy, and the Standard Deviation of 38 is nothing to brag about. But those variations in velocity won't show any effect on the target until you start shooting at a distance where velocity actually matters.
50 yards isn't it.
CM

Well, that's depressing. Here I was all happy about my first chrono results since I find the loading very accurate out to 10 yards from a .357 snub.

http://castboolits.gunloads.com/showthread.php?t=95362

HangFireW8
11-20-2010, 11:14 AM
Well, that's depressing. Here I was all happy about my first chrono results since I find the loading very accurate out to 10 yards from a .357 snub.

http://castboolits.gunloads.com/showthread.php?t=95362

A 357 snub is going to have a high Extreme Spread of velocities no matter what the load.

Unless you are going for 100 - 200 yard shooting with your snubbie, your accuracy results at 10 yards are all you need.

-HF

Larry Gibson
11-20-2010, 11:37 AM
As I stated; It's all relative to the firearm, sights and cartridge being tested. Some very close (relatively speaking) ES can be had with some loads out of "snubbies", even with .357 magnum loads. I've gotten less than 60 fps ES for a 6 shot string with several .357 loads out of my 2 1/2" M19 and a 2" M10. Also, just to point out that some have different expectations for "snubbies", if you shoot in the "snubbie" match at a TRC or PPC match you'll need very good accuracy (X/10 ring on a B27 target) to 25 or 50 yards.

The point is that the information provided by the chronograph in addition to the group provides much greater quantitive information about the load. Taking the .357 "snubbie" for example; if I have 2 loads that both produce 2" 12 shot groups at 25 yards choosing by group alone would just be a guess. However if one load gave 135 fps ES and the other gave 75 fps ES there is no doubt which one I would choose and which would be the best load.

Larry Gibson

44man
11-20-2010, 02:15 PM
I never, ever work loads over a machine. I go only for consistent groups all day and the smallest I can get.
I have been down to a 1 fps deviation with groups done better by throwing rocks.
Leave the numbers and machine at home.

Larry Gibson
11-20-2010, 07:45 PM
I never, ever work loads over a machine. I go only for consistent groups all day and the smallest I can get.
I have been down to a 1 fps deviation with groups done better by throwing rocks.
Leave the numbers and machine at home.

Obviously some of us aren't up to your abilities (1 fps deviation...wow, was that with a 10 shot string?) and need all the help we can get. That's why we take the machines to the range and pay attention using the numbers in conjunction with the group size to determine what loads are working best, it works for us.

Larry Gibson

shooter93
11-20-2010, 09:48 PM
I pay little attention to SD early on because I believe it takes a large number of rounds fired to give you a TRUE SD number. I do however watch ES closely. Everyone has their own set of standards for accuracy...mine is 10...10 shot groups (5 ten shot groups minimum) fired at 100 yds minimum. I feel this gives me a true picture of the guns accuracy. I also want to know the the accuracy level for those 10 shots from a cold clean barrel to a warm one. Match guns ofcourse being an entirely different animal. A high ES is murder at longe ranges but as stated it may mean little practical hunting ranges and iron sighted guns. Each application for the given gun needs to be decided then you can evaluate you chrono's data accordingly.

MtGun44
11-20-2010, 11:40 PM
Load testing at 50 yds for a rifle is pretty inconclusive unless it is really bad.

Move back to at least 100 if you want to be able to see if the load is really
worth keeping.

Bill

Larry Gibson
11-21-2010, 01:47 PM
shooter93

Excellent proceedure, much to be recommended there:-)

Larry Gibson

44man
11-21-2010, 04:23 PM
Obviously some of us aren't up to your abilities (1 fps deviation...wow, was that with a 10 shot string?) and need all the help we can get. That's why we take the machines to the range and pay attention using the numbers in conjunction with the group size to determine what loads are working best, it works for us.

Larry Gibson
That was with BP in my 45-70 BPCR for 10 shots. Shot HORRIBLE!
Now my best load in the .44 with a 320 gr LBT has an SD of 11.5, MAD of 9.9 and ES of 29.
What we do is find the most accurate loads that do not change day to day, month to month or year to year and chronograph them to see the velocity. We ignore the other figures.
If every single shot was the exact same velocity, I don't think it will make any gun shoot better.
If your twist or gun does not like a boolit or bullet it does not matter what your figures are. You could burn 5000 rounds with the wrong bullet or velocity with a zero SD and not hit a thing.