Advice Needed: Statistical Samples from (Len,Wt) to measure MV

[CrimsonApostle]

You don't have time to reload or go to the range but you want to be successful at long range. Won't happen no matter what your statistics tell you. Bench technique, gun handling and understanding wind conditions, temperature and other things can only be learned by shooting or mentoring. If your trying to teach yourself it's very difficult.

Sigh.... I said in my original post that I had had some long-range classes, and I quoted Litz' book and have read others, and the guys at the Missoula range are GREAT about sharing info. And now I have 4 Litz DVDs to watch soon. So I'm not trying to teach myself. And I said in my followup posting that I am NOT trying to be competitive.

And who said I don't have time to go to the range? I am trying to improve and better understand my results when I do go there!

 

[Luke_NL]

I won't go into the factory rifle debate, as I do believe there is some merit in squeezing performance out of what others deem but marginally fit. I am just now getting into semicustom rifles, butonly because I feel I may now be able tell the difference.

Have I missed the part where you debated these issues with the guy you paid to deliver custom match grade ammo? If not, I would get back to him and discuss the 40 fps MV spread because that is going to hurt a bunch at longer ranges. When you order(ed) ammo for long, long range (and I would not, but my s.o. is mostly forgiving for the time spent between work, bench and range) did you agree on a regimen for the loaded rounds and detailed specifics? Sounds like you may have paid for apples when buying oranges.

Imho, you should debate (and pay for) a regimen that should include fireforming new (quality) brass, sizing to length, trimming brass, neck uniforming, consistent chamfering, powder within very strict margins, measured and selected bullets (weight, lenght of base to ogive) and possibly tipping or meplat uniforming. AOL should then be uniform. Concentricity of the rounds is also a concern, but easy to measure. Dizzying really, but if all steps are performed well, mv variation should ideally be as close to zero as is possible, although I have yet to see anything under 10 fps consistently.

If your guy only provided a five shot group as proof for the quality of the ammo, I doubt whether all the above was followed to a tee. Simply put, you may have to get better ammo. Rather than shipping out your rifle, see if one of your range contacts may be able to sort you out for a price. Personal involvement is sort of necessary as top notch ammo is a labor of love for the most part, or really really tedious without the love. Easy to let things slide.

Good luck on your efforts. Don't take all criticism to heart: I for one have certainly spent time loading and shooting ammo that I would have better spent reading (here and elsewhere) on the how and why of things. Live (shoot) and learn.

 

[CrimsonApostle]

Luke,

THANKS! Glad to not get flamed yet again for a sincere question on my first topic posted to any AccurateShooter forum. I have about 800 rounds, including 540 from CC, and its not in the budget to buy or make any more so I need to get the most out of what I have. I think that it is euphemistic to describe the attitude of most who replied regarding my rifle as "marginally fit"!

I have not yet talked with the manufacturer of my semi-custom ammo. I will be at the range in a few hours measuring MV on chosen rounds. After this I will contact the manufacturer, CC, and also MM who recommended them to me (he seems somewhat high profile, or at least plugged into a lot of places. so that may put more pressure on the vendor).

I'm not sure what I should reasonably expect them to do, if anything, to remedy this situation. I also did not agree on a regimen for the loaded rounds .... they were supposed to be able to make things better than factory ammo that was tuned to my rifle; I did not know to ask more. CC only provided a 3-shot group from 100 yards as any kind of proof. And I agree that CC likely skipped most of the steps that you mentioned. But at about $2.10/round I don't think that I could have expected most of those steps, but of course should expect that it performs better (and certainly not significantly worse) than factory match ammo. And I'm pretty sure that I don't want any more ammo from CC. Caveat emptor perhaps.

Its not in the cards in the next year, and then I'm very likely living in Germany for a year. After that it may well be possible to upgrade rifle or at the very least get some very good ammo made for me.

Thanks again Luke!

 

[Grimstod]

Ok Crimson let me get this straight.

You want to know what sample size you should take from your lot of ammo?

You need to know
1. Z-score
2. p
3. q
4. e

Here is your formula

p is the probability of success (minimum variability)
q is the probability of failure (maximum variability)
e is the confidence interval that you select
Z-score is a number you have to get from a statistics book and you won't find it in a 300 level class book. I will give you a few numbers to start.
If you want an e of 90% or .10 then use a Z-score of 1.645
If you want an e of 95% or .05 then use a Z-score of 1.96
If you want an e of 98% or .02 then use a Z-score of 2.326

If your a plinker then probably 90% will make you happy if your a competitor then 98% is going to be your ticket.


If you have a small population it will decrease sample size slightly.

n sub 0 is the sample size derived in the first formula.
n is the sample size and N is the population size


Another way to do it
Since you already know your SD or Sigam often represented as s, then use this formula I use on my iPad. Its the attached file.