Some of us--and I ain't naming names--are doing good to get through the whole day w/o breaking itI've heard and read this quote a thousand times over decades--my question is has such a rifle ever truly existed? Seems impossible to me.
Sub MOA all day long
- Thread starter stagpanther
- Start date
Yep that's why I posted those groups above . I've shoot 10 shot sub moa groups more then I would have thought I could but that does not mean I do it all day long . As load development progresses in 5 shot group increments , once I've settled on a bullet , powder , charge weight and seating depth that I think is my best combo . I then go out and shoot 2 o 3 ten shot groups with that load to confirm it is actually good . That is when I've shot those ten shot groups above . I generally only shoot 5 shot groups except in final testing . If I can shoot 10 shots in a row 3 to 5 seconds apart at sub moa , I call that load gtg . That is not to say every 5 or 10 shot group with that load will be sub moa but is a good indicator the load is good .
I don't believe because I shot a 10 shot sub moa group that is a good sample of what I'll get with 100 shots . The problem with groups is that they can only get bigger the more shots you fire . It's not like that 1 moa 10 shot group will ever be a 3/4 moa group if you keep shooting . The best I've ever done was a 16 shot sub moa group at 100yds . I was shooting one of those test loads once and shot 10 at sub moa so I just kept loading and shooting to see how many I could shoot sub moa . The 17th shot was WAY high and to the right by about 1.5in from the rest of the group . I wish I would have kept shooting or later investigated what caused that shot to miss so badly . It felt good and was not called high right it just went there and I just stopped shooting and called it a good load .
Last edited:
stinkypete said:
Unfortunately, that doesn't work out very well because, on average, groups always get bigger with sample size because the more shots you fire, the more chances you give less probable results to appear, so the more likely it is you will get one. For example, you wouldn't expect a 2-shot group to be representative of your typical 4-shot groups. You'd expect the latter to be bigger. The stats say it will be 1.8 times bigger, on average. So the square root rule has problems in small sample sizes. My old company's manufacturing statistician said the sample should be the square root of the total number of items in a run (the population) or they should be thirty, whichever is larger. This is for the purpose of estimating population standard deviations and mean value, though, and not for estimating the extreme spread, which always has a random element.
The first plot below shows how much extreme spread grows with sample size for the same SD. For example, for a 9-shot group, the ES is expected to be about 3 times the SD on average. For a 27-shot group, ES is expected to be about 4 times the SD on average. And for a 95-shot group, ES is expected to be about 5 times SD on average.
Below that plot is another that shows the 95% confidence limits for sample size. You can see in that lower plot that a sample of 2 has very high upper and lower limits that subsequent samples of 2 might turn out to have as the difference in extreme spread between the two samples. The closer those lines are to the average, the smaller the difference your next sample that same size is likely to have. You can also see that by the time you get to 30 samples, the spread is no longer converging very fast.
The bottom plot also shows, though, that a sample of ten is fine as long as you are satisfied with 95% confidence limits in expected variation from one sample to the next that fall within those plotted limits. For ten, it's within about ±20%. That's part of the fun with this stuff. You get to decide how certain you need to be. But if someone tells me they will build me a 3/8 moa rifle, I will want to know for what group size and confidence level and at what range I can expect it to shoot 3/8 moa. Otherwise, even for a machine rest, the number is meaningless. For example, we can all stay within 3/8 moa group diameter with any gun for a 1-shot "group".
Attachments
One thing that I found interesting is the difference in effect between group size and group placement.
In the series of target pictures posted above there are two which illustrate this. There is a 10 shot group of 0.85” and another of 0.97”.
The smaller group scores 88. The larger group is a 95.
Just an observation.
In the series of target pictures posted above there are two which illustrate this. There is a 10 shot group of 0.85” and another of 0.97”.
The smaller group scores 88. The larger group is a 95.
Just an observation.
stagpanther
New member
Just means they aren't trying hard enough.
darkgael said:
It's one of the basic problems with evaluating POI. Not only do group sizes vary, so does their center location wander around, though it wanders less than extreme spread (group diameter). This is because extreme spread (group size) is based only on the two holes, while the group center is influenced by all the holes in the paper. It turns out that the standard deviation of how much the group wanders around is equal to a number called the standard error. To find it, you divide the standard deviation of the whole sample by the square root of the size of the sample. So, for those 10-shot groups, you could expect something like the SD/3.16 is the amount the mean would wander around.
As to group placement in those groups above . All those groups are either different loads or different rifles . When testing a load I don’t care the POI as long as my POA is consistent. The reason the POI is not centered on the target is because any given rifle I have is sighted in using one specific load and those loads above ain’t it . I rarely shoot for tight groups once a load is set and rifle is sighted in for that load . At that point I’m more of a hit the target type of shooter rather then a bunch of tiny little groups shooter .
Same here. One rifle, one load, zeroed at 200 yards from the bench. Plenty of Thump and -1 to 1 1/2 MOA is all I'm looking for from a hunting load. If it holds that to 300-350, I'll use that load indefinitely.
From then on, it's pick an object/animal and hit it from field positions.