Test group count

[Jim]

Because I can't shoot here at the house, I work up loads to test and take them to my shooting place. I started off working up loads of 5 each. I have since reduced that to groups of 3 each. When I find a load that gets close, I switch from 1 grain increments to 1/2 grain increments.

Responses?

[bullshot]

Jim
I do kinda what you do. I load five rounds each powder weight. Shoot and record the best load or loads. Then I load 5 more of the best load and go a half grain either side of that load, again picking the best load or loads. Then I load ten of the best load or loads and shoot them just to make sure that they still are performing good. Wouldn't be the first time all the stars and moon lined up when I shot a great group never to happen again.

[joeb33050]

This is an interesting question.
There are two articles in the book that deal with how to work up an accurate load.
This question is about how many shots per group, in how many sets, in what powder increments, should be shot while searching for an accurate load.
I think the powder charge increment is most easily dealt with. This is about rifle cartridges. I believe that increments of less than 1/2 grain yield accuracy differences that are undetectable 99.9% of the trime. Thus, powder charge increments of 1/2 grain or more are adequate. (I recently tested loads with 2 grain increments, from 16 to 18 to 20 grains. All under maximum in the reloading manuals.)

For most common cartridges there are cast bullet and jacketed bullet loads in the available reloading info, in books or on line. These sources will identify maximum loads.

Unusual or uncommon cartridges have loads in "Cartridges Of The World", that will help.

I shoot 5-shot groups. There are several reasons for my choice, none that are provable or mathematical in nature.

Brent Danielson is an exponent of the 2-shot group, and has some mathematical reasons for believing that 2 is better.

The Creighton Audette Ladder Test and the Dan Newberry Optimum Charge Weight methods use very few small size groups. I spent a lot of time and shots to end up disappointed with the Audette method, which did not work for me at 100 yards at low velocities with cast.

There's a Savage Model 10 in 308 Win waiting for me to test it for accurate loads. I have loads with IMR4227, A#9 and 5744 with 314299, and when the range opens in November, will test in sets of five 5-shot groups. I'd bet that most to all of the loads will shoot under 2" averages, out of the box, OR that there's something wrong with the gun.

So, for a well known cartridge, bullet, powder combination, I believe that sets of five 5-shot groups is the answer.

I think that for 90% of the rifles out there, there is a bullet and powder combination that will shoot under 2" at 100 yards the first time out, IF any load will.

For an unknown cartridge shooting an unknown bullet, I shoot Unique in appropriate charges, loaded at the range, 1or 2 or 3 shots at a time. I start low and increase the charge in ~1/2 grain increments. When I get in the vicinity, I go to sets of five 5-shot groups.

joe b.

[Bret4207]

The more groups you shoot, the better the idea of how that group is performing. Even the great Ken Waters, a man whose experience, knowledge and judgment far surpasses anyone else I've ever read, often stated on a second try with a previously disappointing load he would find things had changed. 3 shots might give you information, or they might not. Add in barrel condition, wind, temp, humidity, mirage, that little crick in your back...the more rounds, the better IMO.

FWIW- When I find a load I think really has potential I try 5 groups of 10 shots. That will give you a real idea of whats happening. But, I have my own range and can shoot out to 4-500 yards if I want, further actually, anytime I want. You have to find a system that works for you.

[Echo]

It all comes down to 'How Accurate in my Estimation do I Want to Be'. Two-shot groups tell us something. If we go to 3-shot groups, we will have a little more faith in the decision we make as a result of the three shot groups. Five-shot groups are even better, but do ten-shot groups improve our understanding enough to justify the added (double!) effort? And do five repetitions of the five-shot groups improve our understanding enough to justify the added (Quintuple!) effort? The added exposure to error mentioned by Bret has to be considered.
>
For me, five shot groups are sufficient...

[Down South]

With a revolver or pistol, I'll make 50 rounds of each load. Once I find one that I like I'll start tweeking on it till I have it like I want it.
With a Rifle, I make 10 rounds of each load. That will give me two five shot groups to compare.

[mike in co]

nothing really matters till you pick the load and PROVE it.

at that point the proof is based on the type of shooting you do.....

hunting could be 5 three shot groups, target work might be 5x5 or 5x10......

in a pistol several full capacity targets( 1911...5x7,8; revolver 5x6. etc)


its not just one or two groups, its the average of real life........5 or more groups shot at real world distances.

mike in co

[405]

I usually shoot 5 shots for measuring a group. My powder charge spread depends on the overall powder charge. For example: If I'm testing a 3 gr charge in a handgun then .1 grain increments become important. For anything larger than a 15-20 grain overall charge then I usually change increments by 1-3 grains.

Powder is not the only variable in load testing. Many other variables need to be taken into account or isolated.

Usually I'll load in groups of 7 rounds for a test. I'll shoot two foulers off target, let the barrel cool some, then shoot 5 for group. I won't do this for more than about two strings because leading or fouling can affect subsequent groups. If I continue to shoot test group after test group without cleaning the bore and cooling to ambient temp then I'm not confident that the groups shot before (accumulated fouling) won't affect the subsequent tests. If I have time I'll take 2 or 3 guns to the range at one time and test two different loads in each. At home the guns will be completely cleaned. The results will be recorded in the load log book. If I can get a load to shoot accurately for three 5-shot-groups, shot at different times, I'm fairly confident that load is accurate in that gun.

[Jim]

Thanks, fellas.

[BeeMan]

I saved and reviewed the sighter targets from a year's worth of military bolt rifle matches. The group and score targets are placed over the sighter for around 60 rounds total on the sighter. Yeah, there is some spread due to sight adjustments for light conditions. With this data it is a pretty safe bet to say where a rifle, load, and shooter will place a shot.