jerkface11
Member
Whoa what are you shooting that eats barrels that fast? And why does a rebarrel cost $700?
thoughts on 3 vs 5 shot groups
- Thread starter taliv
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260 AI
if i shoot 3030-3050fps i get about 1500 rounds. <2960 i get maybe 2400-2600 rounds. at 3000, i get about 2000 rounds. maybe not always but that's my experience over 6 barrels.
$330-350 for a bartlein blank. usually $400 for the plumbing. including cut to length, chamber, thread muzzle for suppressor and cerakote.
if i shoot 3030-3050fps i get about 1500 rounds. <2960 i get maybe 2400-2600 rounds. at 3000, i get about 2000 rounds. maybe not always but that's my experience over 6 barrels.
$330-350 for a bartlein blank. usually $400 for the plumbing. including cut to length, chamber, thread muzzle for suppressor and cerakote.
Flatbush Harry
Member
taliv,
Don't get bogged down in small sample statistics...and std. dev'n. is an estimator of a population dispersion number, keep in mind that the s.d. is a statistic that shows the range covered by 68% of the observations about the average, which is an estimate of the mean of the population of shots.
Consider that that the average and the the s.d. give you an idea of the average and consistency of the velocity of a small set of your loads...no more, no less.
Cheers,
Harry, statistamagician (or M.S, Operations Res'ch/Applied Math.)
Don't get bogged down in small sample statistics...and std. dev'n. is an estimator of a population dispersion number, keep in mind that the s.d. is a statistic that shows the range covered by 68% of the observations about the average, which is an estimate of the mean of the population of shots.
Consider that that the average and the the s.d. give you an idea of the average and consistency of the velocity of a small set of your loads...no more, no less.
Cheers,
Harry, statistamagician (or M.S, Operations Res'ch/Applied Math.)
When I read it most of the concern was the statistical variance introduced by using a smaller number of shots in the group. It was shown it could be a significant factor when calculating a change. Like the sloppy scope screws, the swing back and forth attempting the narrow the results actually meant you have to shoot more ammo to discover where the sweet spot is.
Since its a math operation issue, then it also affects all the other measurements of data, too. Smaller sample sizes have more error, shooting ten eliminates most of it so that other factors become the variables - seating depth, powders, neck concentricity, etc. If the sample sizes are small enough they create most of the variance, it's hard to see what's causing the differences.
At least that is what I took away from the discussion. My concern is to eliminate creating a variable so that with the tools at hand, the items that are creating group dispersion aren't clouded in the data. Determining accuracy has it's own standard, using accurate measurements and a process to derive an accurate answer. If the "scope screws" are too loose, it's an exercise in frustration.
We dived off into a lot of discussion about the tools of measurement, the link was to a discussion about the mathematical methodology of analyzing the results. If the method used is creating the error, then the resulting conclusions will be based on error.
What you are seeing with 5 shot groups is a more accurate picture of the actual group size of a shooter with that rifle. Sample size of the group will generally be more accurate with a larger number of shots than smaller. Three good shots is fun, five is, unfortunately, more realistic, and ten about sums it up.
I think what you are observing is quite factual - it's the natural result of a larger sample size. If this is really a discussion about the tools used measure it, my bad.
Since its a math operation issue, then it also affects all the other measurements of data, too. Smaller sample sizes have more error, shooting ten eliminates most of it so that other factors become the variables - seating depth, powders, neck concentricity, etc. If the sample sizes are small enough they create most of the variance, it's hard to see what's causing the differences.
At least that is what I took away from the discussion. My concern is to eliminate creating a variable so that with the tools at hand, the items that are creating group dispersion aren't clouded in the data. Determining accuracy has it's own standard, using accurate measurements and a process to derive an accurate answer. If the "scope screws" are too loose, it's an exercise in frustration.
We dived off into a lot of discussion about the tools of measurement, the link was to a discussion about the mathematical methodology of analyzing the results. If the method used is creating the error, then the resulting conclusions will be based on error.
What you are seeing with 5 shot groups is a more accurate picture of the actual group size of a shooter with that rifle. Sample size of the group will generally be more accurate with a larger number of shots than smaller. Three good shots is fun, five is, unfortunately, more realistic, and ten about sums it up.
I think what you are observing is quite factual - it's the natural result of a larger sample size. If this is really a discussion about the tools used measure it, my bad.
MagnetoSpeed responded to my query and said their clock is 12 Mhz and they resolve the bullet crossing time in a single cycle so not a problem to resolve that low. They also said their testing against high speed footage (which also has some small error in it) showed a deviation of .1% in velocities around 3000 fps. So basically 3 fps.
Owen
Moderator Emeritus
That's probably of 6fps, normally distributed, because error budgets are generally +/- tolerances. IOW as much as 2fps of your SD may be induced by measurement error in your chrono.
As a rule of thumb, SD should be about 1/3 of ES. If this isn't roughly true, than you have something causing the distribution to be non-normal.
As a rule of thumb, SD should be about 1/3 of ES. If this isn't roughly true, than you have something causing the distribution to be non-normal.
The_Next_Generation
Member
Owen brings up a great point. However, it is interesting that the clock reports values that are consistently inconsistent with the first three shots.
We should also consider that the difference shown could not be extreme enough and that inaccuracy in the equipment could mean that a spread that is reported to be 6fps may actually be larger (the chrono could be 3fps low on the first and 3fps high on the last, meaning the actual velocities would be farther apart than reported).
The fact that the last two shots are always different throughout the data is significant and should not be dismissed as equipment error IMHO.
We should also consider that the difference shown could not be extreme enough and that inaccuracy in the equipment could mean that a spread that is reported to be 6fps may actually be larger (the chrono could be 3fps low on the first and 3fps high on the last, meaning the actual velocities would be farther apart than reported).
The fact that the last two shots are always different throughout the data is significant and should not be dismissed as equipment error IMHO.
You are burning to much powder for a 6.5 bore. If it were me next time the barrel came off a 7mm-08 would be going on. I bet you would get lot more barrel life even though it is a .5 mill difference and would shoot just as flat with the amazing 168 Hornady A-Max at I think .629 BC
Owen
Moderator Emeritus
I don't think there is enough data to say there is a definite pattern.
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