Standard Deviation

[Miseryguts]

Hi, I reload several calibres - both pistol calibres and centre fire rifle. When I pass these rounds over the chronometer, I see SD in the teens and twenties - is this typical? I admit the press and dies are not exactly rolls Royce(Lee kit and Chrony chronometer) but I do take a fair bit of care with the loads. So, is it me, should I get better kit, or am I missing something? Any pointers or criticisms gratefully accepted.

 

[VarmLR]

Achieving single figure SD's can be quite demanding depending on the brass , kit, primers used and all sorts of other variables. Not knowing what you use from components to reloading kit can't help answer the question as to whether your specific SD's are "typical" but achieving teens isn't too bad and I'd say pretty typical where care is taken.

 

Depending on brass used, you can have case volume variations which could account for several fps difference between rounds, you could use primers which themselves vary in terms of consistency of burn for the main charge. There's records on here of where primer choice alone counts for a surprising deviation value, with some being 5 to 10 more than others.

 

You can achieve single figure SD's using very modest kit. I've achieved single figure SDs on my .223 loads for example using modest kit.

 

You also haven't mentioned your sample size. Many record SD's on just a handful of shot strings, when really you need to be shooting strings of 15 to 20 rounds to get any sort of statistically significant results.

[bradders]

When people talk about Standard Deviation, I always point them towards this article written by a very good friend of mine

 

http://www.accuracyspeaks.com/PDF/STANDARDDEVIATION.pdf

[gbal]

Miseryguts, Varm's post is pragmatic and makes good points;Bradder's refered article is making the big point-that target strikes are ALL that matter (the authors are clearly not statistically very savvy,as they admit-grouping arbitrarily fired shots in 5s has no merit at all) but their main point holds reasonably-what effect does SD variation actually have-at the target.

 

 

SD of MV has an effect-if you shoot at 1000y and reduce your SD from a (very good )single figure to a low single figure (few do) ..you will have about a 1mm reduction in vertical dispersion.

If you shoot targets larger than marbles at distances less than 500y,there are far more pressing concerns (atmospheric flatulence).

Bear in mind that Varm gives other sources of SD variation,that are not as easy to control as eg powder.

 

I hope this allows you some peace of mind over Easter.....don't rush to radically upgrade quite yet...

 

I think It's about time for a detailed post on this general topic -what really matters,and how much,and what can be done...watch this space!

 

gbal

[VarmLR]

That article that bradders links to is a very good and worthwhile read.

 

Picking up on a few of gbal's points above, there is also the consideration as to what SD tolerance you actually need rather than think that you need. Obviously, achieving the terminal ballistics you require can mean very different set-ups and loads depending on range and conditions. If you're only shooting to say 300 to 400 yards, you may not notice much difference in grouping of the vertical spread anyway, whereas competition shooting for precision at say 1000 yards may well demand pretty tight SDs.

 

In general terms, I do think that people have a tendency to over-think things like this, whilst paying scant attention to environmental factors and shooting technique, relying on sighting shots during the day's outing. Things like reading the wind and assessing differences at long range of other ballistic and "atmospheric flatulence" issues such as (I like that one George!), spin-drift, temperature, pressure and humidity have far more impact on results, shot to shot, for most of us before we even begin to consider SD values, although arguably, they're something that we can control to a degree.

 

Also, when assessing groups, as George mentions, shooting 3 or 5 shot groups tells us relatively little. This article, linked to recently on another forum is well worth a read as it gives an unusual and thought provoking insight into the whys and wherefores of grouping significance and how to properly assess the significance of your results on group size. http://www.ar15.com/forums/t_3_118/279218_The_Trouble_With_3_Shot_Groups.html

[Chanonry]

Miseryguts, i know the feeling. If we are going to go to the effort of reloading then we may as well do a 'good' job. So the question becomes - am I doing a 'good' job, and how can I be sure that I have believable numbers?

 

Before tearing your process apart and buying a load of new kit I would chrony it over a (borrowed) magnetospeed. I had two Chrony's (shot them both) and was never really happy with the numbers, but my use of them lacked any sort of sophistication.

 

I have made some low sd loads (~sd=9) on predominantly Lee kit, but never with their seating dies. My best loads ever were perhaps for the 223 with the collet die, which amazed me as I really didn't feel confident with it. It was only £30 for the set, so who says you have to spend loads to get quality output.

 

Older brass may be an issue? Saves changing dies only to have the same problem if the neck tension is all over the place.

 

If the reloads shoot well enough for your purposes forget it, if not start with the chrony to make sure you are working off real numbers

[Miseryguts]

Hi,

Lots of food for thought there!! Thanks to all who took the trouble to reply, and for the links to the very informative web pages.

I have had doubts about the veracity of the Chrono for a while, but it is better than nothing.

I take the point about not overthinking this as my centrefire fifle shooting is sub 300 yards, and of the pistol calibres are gallery rifles at 25/50m. Any variations in SD are likely to have far less effect than my shakes.

Thanks again

[Andrew]

When people talk about Standard Deviation, I always point them towards this article written by a very good friend of mine

 

http://www.accuracyspeaks.com/PDF/STANDARDDEVIATION.pdf

I like this guy.~Andrew

[bradders]

I like this guy.~Andrew

 

So do I, that's why we have been friends for nearly 20 years

 

Derrick was on the All Guard team and was a highly respected competitive shot who also won the Fortuna Trophy here at Bisley and is still a highly respected gunsmith

Barrett is an aviation journalist and writes and produces the series Dogfights for the Discovery Channel.

 

If he says "it doesn't matter" then generally it doesn't

[Andrew]

 

So do I, that's why we have been friends for nearly 20 years

 

Derrick was on the All Guard team and was a highly respected competitive shot who also won the Fortuna Trophy here at Bisley and is still a highly respected gunsmith

Barrett is an aviation journalist and writes and produces the series Dogfights for the Discovery Channel.

 

If he says "it doesn't matter" then generally it doesn't

People today, especially the new generation of internet-educated reloaders, spend too much time brain working and not enough time behind the trigger. Five shot chronograph averages? Four shot groups during load testing? I pick a powder and load fifty at one charge weight, then wring them out. If there are no glaring faults I repeat the process. By the time I'm done I know with a high degree certainty how accurate the load is and whether or not the load will work for its intended purpose; or at least will be certain if it won't.~Andrew

[bradders]

People today, especially the new generation of internet-educated reloaders, spend too much time brain working and not enough time behind the trigger. Five shot chronograph averages? Four shot groups during load testing? I pick a powder and load fifty at one charge weight, then wring them out. If there are no glaring faults I repeat the process. By the time I'm done I know with a high degree certainty how accurate the load is and whether or not the load will work for its intended purpose; or at least will be certain if it won't.~Andrew

 

Indeed, you only have to look at those that kill themselves over their searing depths. On the lands, off the lands, jammed...and by how much?

I've never seen anyone post about readjusting seating depth during the barrels live while chasing the throat, likewise, you only ever see the 'best' groups posted

[Andrew]

I know this is blasphemous talk on a 'precision shooting' forum but I always tell new reloaders to just follow the instructions in their reloading manuals, exactly. The kind of instructions that come with the Lee Classic Loader: Size. Trim. Prime. Charge. Seat to recommended OAL. Shoot. Do all these steps well and nothing else. Success is pretty much assured.

 

Internet beginners get so deep into the weeds that they can't see that it's not what you do as much as how well you do it. JMHO, of course. ~Andrew

[MTLEADFARMER]

In your blasphemous rant you forgot CRIMP

[John MH]

People today, especially the new generation of internet-educated reloaders, spend too much time brain working and not enough time behind the trigger. ~Andrew

 

 

Totally agree, you've hit the nail on the head.

[Andrew]

In your blasphemous rant you forgot CRIMP

That's a given........~Andrew

[gbal]

Crimping ,though,is an optional step. I know Lee promote it,but others like Speer do not (as in their literature 'if you want to ruin accuracy,start by ruining the bullet"-with photos of distorted crimped bullets with a din't all round...

Of. Course the case for a crimp has alwats been to retain the bullet-preferably those increasingly rare designs with a cannelure-better in recoil etc. Claims for enhanced accuracy are weak indeed,and countered massively by bench rest etc with rather light bullet (re)tension,thou carefully controlled. Military practice too has gone for crimp-but that includes crimping the primers too,and that is indeed a rare proceedure for most of us!

My reloading bible doesn't even mention crimping (but then it's "Precision Reloading' by Gravatt and Sinclair),but of the 4 or 5 'standard' manuals,really the advice is as above-if you have a light fairly noticeable recoiler,and premium accuracy isn't top priority,then try it-with cannelure bullets (no fiddling with seating depth then!)...and I might if I was shooting a light 30/30 carbine at rather large game (deer) at rather short distances (sub 150y)...though I haven't experienced any loose bullets in several decades of non crimping,typically with b/a,despite some quite vigourous terrain.Of course such crimped ammo is 'accurate'-I've accurate enough for a 6 inch zone-so is effective (it's better than that,typicall-but .5 moa....not much recorded or needed!)

 

More generally,once we introduce words like 'success' without some criteia,we are not likely to progress much-though the term is 'adequate'.....sometimes....but specifically,success in competition shooting is less likely without some attention to finer proceedures,though I absolutely agree these can be overthought-actually not tought about enough,really-a balanced consideration indicates such diminishing returns for second decimal 'precision' that time would be far better spent actually shooting 'adequate' ammo....which is the sort that is made good enough to give above 95% hits-which is beyond many shooters skill -ie shooting solution decision making- typically called wind reading,though that's not it all. The math(s) will reveal this all too well,though most shooters already know it.

 

So ....decent ammo-reloaded or bought-and plenty realistic practice-as long as it is effectively done,but the 'OCD' reloaders are doing their thing,and the more conscientious actually establish guidlines for input/output efficiency for others,who are thoughtful enough to pay heed. If they find a better wheel,so much the better for all who wish to use it.

Meanwhile.live and let miss....but not by so much !! :-)

 

Gbal

[Andrew]

Crimping ,though,is an optional step. I know Lee promote it,but others like Speer do not (as in their literature 'if you want to ruin accuracy,start by ruining the bullet"-with photos of distorted crimped bullets with a din't all round...

Of. Course the case for a crimp has alwats been to retain the bullet-preferably those increasingly rare designs with a cannelure-better in recoil etc. Claims for enhanced accuracy are weak indeed,and countered massively by bench rest etc with rather light bullet (re)tension,thou carefully controlled. Military practice too has gone for crimp-but that includes crimping the primers too,and that is indeed a rare proceedure for most of us!

My reloading bible doesn't even mention crimping (but then it's "Precision Reloading' by Gravatt and Sinclair),but of the 4 or 5 'standard' manuals,really the advice is as above-if you have a light fairly noticeable recoiler,and premium accuracy isn't top priority,then try it-with cannelure bullets (no fiddling with seating depth then!)...and I might if I was shooting a light 30/30 carbine at rather large game (deer) at rather short distances (sub 150y)...though I haven't experienced any loose bullets in several decades of non crimping,typically with b/a,despite some quite vigourous terrain.Of course such crimped ammo is 'accurate'-I've accurate enough for a 6 inch zone-so is effective (it's better than that,typicall-but .5 moa....not much recorded or needed!)

 

More generally,once we introduce words like 'success' without some criteia,we are not likely to progress much-though the term is 'adequate'.....sometimes....but specifically,success in competition shooting is less likely without some attention to finer proceedures,though I absolutely agree these can be overthought-actually not tought about enough,really-a balanced consideration indicates such diminishing returns for second decimal 'precision' that time would be far better spent actually shooting 'adequate' ammo....which is the sort that is made good enough to give above 95% hits-which is beyond many shooters skill -ie shooting solution decision making- typically called wind reading,though that's not it all. The math(s) will reveal this all too well,though most shooters already know it.

 

So ....decent ammo-reloaded or bought-and plenty realistic practice-as long as it is effectively done,but the 'OCD' reloaders are doing their thing,and the more conscientious actually establish guidlines for input/output efficiency for others,who are thoughtful enough to pay heed. If they find a better wheel,so much the better for all who wish to use it.

Meanwhile.live and let miss....but not by so much !! :-)

 

Gbal

You forgot to mention that almost all factory ammo carries some form of crimp. You have talked of those who don't mention or recommend crimping but I have to ask: How many cartridges have you personally crimped? ~Andrew

[Re-Pete]

A couple of really interesting links........thanks for sharing.

 

RePete

[gbal]

Andrew,the thread is about reloading,rather than factory-though I did mention military crimp-and could have added that factory crimping is done because factory ammo has to retain it's integrity in a wide range of rifles,and manufacturers cannot cherry pick which (eg b/a or s/a,l/a etc which may vary in the trauma on the loaded round from magazine to chamber.

Many precision oriented reloaders do vary bullet retention-but using neck bushings rather than crimp.Perhaps more consistent and more control-it is true that virtually all shooting records are made by handloaded ammunition that is not 'factory style' crimped.I have never seen match bench rest bullets with a cannelure.

That is not to say crimping cannot produce 'satisfactory for purpose' ammo-it can,but that purpose is unlikely to be top grade competition winning precision. Speer alleged (in their litiginous spat with Lee,around ten years ago-in which both exagerated the issues) ,the best quality match factory ammo is not factory crimped.I'd have no issue with factory crimped hunting ammo if carrying a l/a carbine 30/30 -more than adequate,if not everyone's choice(but what is? :-)

 

Since you ask a personal experience question,I'll answer-though I do hope this doesn't suggest you take the naive view that actually doing something is the only knowledge worth having (I know Billings is in Montana,but have never had the pleasure of either!

 

38/357 Revolver;357 Win 94;Hornet b/a;223 Mini14;250Savage (99)...all with Lee crimp die.

 

Bushing die: 222rem,222PPC,2x6PPC;2x6BR:7BR;30BR; 5x308w;6.5x55AI;Shehane:-these being various-Wilson,Jones,RCBS Comp;Newton. All were more accurate than any of the crimped-but I'd not attribute that to crimping per se. Normal reloading 17rem,3x243,7x57 all were better than crimp,but not because of the crimp. I did not think to count the number of rounds,but it's over nearly five decades.

I read a bit too.

 

How is Springtime in the Rockies-are volatile BCs etc settling down a bit-not that such measures are all that critical-as I said in the 'crimp' post,there is indeed a very great deal to be said for not pursuing decimal places,and gettin' out and shootin' - though just where the balance lies is individual-and maybe best informed by purpose and the base precision demanded by that form of shooting. I like the 250/99 but crimp or no,it is just never going to be a Bench Rest or 1000y rifle. Woods deer-yep,there is plenty good testimony to that,and it carries/handles very well-both hands,not just first hand. :-)

Atb

g

[bradders]

1) Andrew,the thread is about reloading,rather than factory-

2) Many precision oriented reloaders

 

1) Actually it's about Standard Deviation

2) I love this term "Precision", it's made up and no one really knows what it means when it comes to rifle building or shooting.

 

A "precision built" rifle won't work correctly

"Precision ammunition" what's that?

 

If you wish to discuss "Precision shooting, then take a look at that contraption Geordie has had built.

That should be the epitome of "Precision" but as I learned from Al's thread (who coincidentally holds the UK small group record of 2.778" at 1000 yds for Heavy Gun....shot with a normal rifle) that should be the master of all targets it shoots at, but it turns out that a small group anywhere on that 6'x6' target will do, as long as it's small

How does that equate to "Precision" when they're not even trying that hard?

 

As JFK said about going to the moon, "we choose to do these things not because they are easy, but because they are hard"

 

As for crimping, I run a crimp die loosely set up on the final station of my Dillon, not to actually induce a crimp, but as a final precaution to iron out any blemishes or nicks on the case mouth that may impair chambering or whatever

[gbal]

Mark,it's about the SD of MV of reloaded ammunition....crimp may be one factor.. A detailed description of Standard Devition is clearly needed,but that is statistics,not shooting per se.

 

The justly respected and rightly influential Brian Litz knows what it means*-he has half a book on precision;the other half being about accuracy. They are related,as the book shows,but distinct. Much semantic inaccuracy and imprecision is avoided by adopting Litz' distinctions.Cal Zant (eg) of the Precision Rifle series blog does so...at the very least,usage of the Litz terms makes VERY clear what is meant.

 

The essence,if you don't have it ,is that Precision is the minimisation of bullet dispersal in the rifle/ammo,very simply 'small group'potential' while Accuracy is the shooting solutions the shooter makes with his gear to place that group where he wants it-simply, 'hitting the bull'' - via wind reading,clicking on scope,steady hold etc etc."Precision" -is the 'engineered intrinsic consistency of the rifle and ammo;"Accuracy' is the shooters contribution to POI coinciding with POA;I've added 'scope/trigger/rests ' and the like-whose qualities help the shooter bring out the precision ,and give accurate shots.

These three 'categories' help distinguish the demands of different shooting disciplines (and so the priorities of the shooter.)

(The distinctons for shooting stand on their merits,but I have been influenced/impressed by similar clarifications in Linguistics and Cognitive Psychology between Competence (what the system must have) and Performance-how it operationalises these 'must haves' within its strengths and limitations.Or even more widely/influentially-'nature' (genes) and nurture (environmental experience)-so much obfuscation was removed by these distinctions- revolutions.but meanwhile.....

 

The (new) heavy gun you mention has only had one outing so far,and Alan's shooting was,by definition,the best ever-so perhaps not typical (I don't mean by Alan,I mean with a ''normal' rifle -an AI rebarreled by Al,if Darrel will forgive this basic description. It has very high precision,and probably wewill allow accuracy-at least for exceptional shooters.

 

I have some empathy with the 'group anywhere on target' point,but I think Diggle 1000BR is now also using score (measured by the familiar rings from the bull out.) This will make much 'criticism' of BR obsolete. Sub 1/2 moa 5 shot groups all in middle at 1000y is quite impressive,

CSR is impressive too,done well. The precision /accuracy/skill mix is just a bit different.

 

Track and field athletics decathalon (yep,done it first hand/leg etc) has always seemed a good model-ten athletics events,points in each for how closely you get to the world record in each....prefering shot put to pole vault is a prerogative,insisting it's superior is more a prejudice.cf CSR and BR,if you will...

:-)

gbal

 

 

 

 

*It's just not true to say 'no-one knows what the words mean",only you can really say if you do If you resist 'LItz',and you have a better conception of the distinctions,by all means present it....the distinction though is much used-eg Formula 1 'the car' and 'the driver' (and 'the team' to optimise the interaction...it's hardly... errr...Rocket Science,though Bryan is well qualified there too.... :-)