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How many rounds, per firearm, make a representative sample for a particular charge weight/propellant/projectile/primer/cartridge overall length combination, when working up a load for a specific application?
Obviously, 50 to 100 rounds would give LOTSA information on extreme spread and variance, but that's a lot of components to use, especially in initial stages. Five or ten rounds seem(s) too small, but might tell the shooter whether there is potential (for hazard OR superior performance), depending on the round of interest.
Let's say we're trying to make "major" for USPSA with a .40 S&W or .45 ACP. Bullet Weight x Muzzle Velocity, divided by 1000, must equal or exceed 165. Because Murphy's law is our constant companion, we want a 3% margin of comfort, in case their chronograph clocks differently than ours, so our goal is a PF of 170. We need 850 f/s with a 200 gr. projectile, or 920 f/s with a 185 gr. projectile.
CERTAINLY, as we shoot a particular load over time, we'll learn whether it's what we're after. But when we're at the bench, trying to balance economy of components against certitude of results, what number of rounds for a certain (untried in OUR firearm) load combination seems a valid compromise?
As a B.A.G., I'M inclined to think that three full cylinders (15 to 24 rounds) is enough for most revolvers, and 20 rounds is about right for most auto pistols. There's nothing MAGICAL, to me, about 3 full cylinders being about right for revolvers. My decision about this amount is completely arbitrary, except that, intuitively, it seems reasonable.
Thoughts?
 

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I retired as a quality manager for OE auto parts production. I’m not going to go into statistics on this one as we would in auto manufacturing, but simply say that the more you check the higher the confidence level is. For “real world” assessment, a sample size of thirty is pretty good. The closer you get to that number the more reliable the data is. Since this isn’t critical data, your numbers aren’t too far off. Nothing says you can’t add on to the sample size over time and increase the reliability. In fact, good statistical data collection is better over time to capture more variables.
 

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Three rounds tells me what I want to know. I'm gathering information, not statistics.
I was gonna say 5 :)

I don't sit out in the frozen weather to see how fast my bullets are going, and when the sweat is dripping in my eyes, same. But a real chrony fan probably would. These days bullets are kinda' scarce, and the price is going up, I might drop back to three myself.
 

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I shoot 3 shots and collect velocity and group information. Now many will tell you that 3 shots is not enough to tell you if you have a really capable load for SD or group, and they are right. But I have shot enough groups where when I looked at the velocities or group size after the third shot, I knew that shot 4 and 5 were not going to help.

In short, 3 is enough to rule out a load most of the time, but not always enough to prove it.
 

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The Hog Whisperer (Administrator)
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3% is a pretty thin margin, unless you are going to fire off a bunch of rounds. I'd think ten at least to have any confidence in the results. Even then, you could have a sample biased toward one end, and whatever small sample is checked at the competition, could be biased the other direction.
 

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The Troll Whisperer (Moderator)
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When testing for indications of best velocity/accuracy, my procedure was to shoot 3 - 5 shot groups over the chronograph with impact at 100 yds. Figured to throw out the highest and lowest of the groups would give me a reasonable base. 3 shot groups make a pretty picture for bragging, however, 5 shot groups will tell the tale much better. Naturally, barrel heat and sight pictures come into play.
 
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The number to be statistically valid is pretty high….not something I aspire to. Long shot strings are a “freak hunt”; are looking for the worst occasional shots.

Some times it’s 3…. might only take that to figure out it’s not what you were after. If you found some “freaks” with just 3 rounds, it’s not going to get better.

Memory has Speer promoting 7 rounds as being cost effective for them. Even if I misremember who it was, been sticking with 7.


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Just to mention…..way back when there were paper screens and no photo screens, we did a whole lot less chronographing.

Pop had a Telepacific...big battery, paper screens, non digital readout...expensive. It took forever to chronograph just a few shots (having to wait for a range all-clear between each shot to change screens).

We lived in blissful ignorance….either it grouped well, or it didn’t…..dropped excessively over range, or was landing where the tables said it would land.
 

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To get a decent "sample" I shoot 4 five shot groups at a sitting and duplicate that process over several months. I shoot a perspective load under different conditions to be secure that the load will give me the accuracy that I need on the first shot. I am a hunter not a target shooter but accuracy is far more important than velocity. Velocity should be consistent to get that accuracy over a wide range of conditions.
 

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May be more a philosophic difference…..either we’re weeding out the bad ones, or we’re polishing the good ones.

First step is to weed out the hopeless loads….how much you test the good ones is a matter of how statically significant is important to you.

Still in that 1960’s mind set (when pop had that paper screen monster)...groups well, drop is as expected, just a few ‘graphed shots….am happy.

Mental cost-benefit analysis of being “happy” vs. statistical relevance leans towards “Happy”.
 

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I won't spend much time, on a short range hunting rifle with open sights, for instance, I'll just shoot some three shot groups with increasing powder charges, watching the chronograph and the groups, decide on charge, test it at 100 yards, and call it day...
For rifles that will shoot at distance and are worth my trouble, I'll shoot 3 shot groups through the chronograph at 200 yards with increasing powder charges for each group looking for the for sweet spots in velocity where ES and vertical spread improve. When I find an acceptable velocity and ES, which is much easier to for me to see in the grouping at 2 hundred yards than a hundred, I will start loading larger groups of 5 varying .1 or.2 either way, looking for the middle of the velocity node I have chosen. I may begin to test with seating depth at this point depending on the particular rifle, or results. When I am satisfied with a load, I will finally load up the rest of that batch of brass and continue to test throughout the year, at longer ranges whenever possible, recording any changes in velocities due to temperature, barometric pressure, etc. By the time a batch of at least a hundred brass casings are fired I'll have a much better idea of ES/SD and reliable grouping at distance.
If I am starting with brand new un-fired brass I will not to spend too much time testing it. I will have to re-test and readjust the powder charge after the new brass has been fired, annealed, and resized anyway. I almost always get better results on brass that has been fired at least once in the rifle. This works for me, YMMV. :)
 

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I was gonna say 5 :)

I don't sit out in the frozen weather to see how fast my bullets are going, and when the sweat is dripping in my eyes, same. But a real chrony fan probably would. These days bullets are kinda' scarce, and the price is going up, I might drop back to three myself.
I would say 5 also but generally use ten. I wonder how much effect of fouling and barrel heat makes on the velocity's you get. Might be do say three shot's at a time for several time and you'll get different number's than shooting 10 shot's in one sitting. Before someone mentions letting the barrel cool, have you ever felt the hot barrel and timed how long it actually takes to get cool again even in the shade? Testing ammo I like to stick to three shot groups just to avoid barrel heat and understanding that an animal I blown the shot on three time I'll probably blow the fourth assuming the animal hasn't left!
 

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Elk Whisperer (Super Moderator)
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I always start low and work up until I get the most accurate load then if I'm curious or if somebody asks I'll chronograph say 3-5 to satisfy "our" curiosity. Too me long shot strings are a waste of my time and components.

The smile on my Marine's face is more important.



Or the grin of a new shooter who also learned to load his own, did his own load development and shot all the groups.



The muzzle velocity (at 25 feet) of my 300RUM with a 180 grain Accubond is 3274 fps which will shoot a 2.385" group at 500 yards. I don't recall the deviation or spread.

RJ
 
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Normally I don't have a specific, limited need for any load, so I don't worry about "shooting too much" of my special handloads, I reload to shoot. I have never worried about a shortage of components, "using them all up testing" as I have always kept a prudent supply on hand, even today. I like all the aspects of reloading from research, gathering components, reloading, testing, analyzing and recording. So, I like 10 shot averages, shoot more, reload more have more fun...
 

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The Hog Whisperer (Administrator)
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If we go back to the original question.... it's about getting an accurate velocity average, to meet the rules of a competition. So, part of that is not only the average, but what sorts of extreme spreads that different loads are giving. Lower extreme spread, less change of showing up for competition and not making the minimum threshold.

That's a situation where "more is better" for sure. If you want to get an idea of statistical validity of small sample sizes, look up Student's T-test.
 

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Funny thing. When I started reloading the velocity we got was what was in the manual. Back then damn few people had a chronograph. Today guy's use one to find out pressure. Seems absurd to me, about like using a lead thermometer to take a childs temp! If the velocity is right then we assume the pressure is also right and we have explanations to prove it!
 

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I have two rifles (Wildcats) I built in the '80s and have shot a combined 5k rounds through that had never been chronographed until last fall....and now I can't tell the results! My only use of a chronograph is to satisfy my curiosity, but I'm not real curious about velocity.
 

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I usually do 5 shots with my Magneto blade type chrony AFTER I've found the load that gives me the best groups. If the SD & ES suck, well, I usually look at the target a bit more. I usually have covered the load charge range per the manual(s), so I usually quit while I'm ahead and find something else to shoot for a while.

A range buddy will NOT fire a shot without his Labradar set up on the bench. He does shoot in the .1-.2's most of the time but only 3 shot groups. Don't think I've ever seen him shoot a 5 shot group for load confirmation. LOL
 
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