Standard Deviation <bullet speed>

[Baldie]

How 'anal' are you? ;) :D

For me, accuracy starts with consistency. [Obvious?] But what are you using to measure your consistency? Powder scales? Group size at the range?

Not me. Bullet speed..... Going back to my airgun days, +/- 5 fps [my BSA Superten] gave supreme accuracy if I did my bit. [Which I could if the temperature was moderate and I was inside a large building. Which sometimes I was. ~ At Pete's Farm in Chelmsford.]


Mechanical consistency is easier to measure than skill, on any given day. Not prone to temp, firmness of rifle, gentleness of trigger pull.

But what does bullet speed 'consistency' look like? In airguns, +/- 5 fps when you're talking about 800fps is very good and can produce a single ragged hole at 50 yards. Ramp that up by x4 and you get .... 3400fps with +/- 20fps and maybe (hehehe) ragged hole at 200 yards?

I've no idea? Do you? :confused:


What is a good 'consistent' (standard) variation at CF type bullet speeds?

I would think +/- 20 fps might be considered quite tidy. ;)


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[Gary C]

How 'anal' are you? ;) :D

For me, accuracy starts with consistency. [Obvious?] But what are you using to measure your consistency? Powder scales? Group size at the range?

Not me. Bullet speed..... Going back to my airgun days, +/- 5 fps [my BSA Superten] gave supreme accuracy if I did my bit. [Which I could if the temperature was moderate and I was inside a large building. Which sometimes I was. ~ At Pete's Farm in Chelmsford.]


Mechanical consistency is easier to measure than skill, on any given day. Not prone to temp, firmness of rifle, gentleness of trigger pull.

But what does bullet speed 'consistency' look like? In airguns, +/- 5 fps when you're talking about 800fps is very good and can produce a single ragged hole at 50 yards. Ramp that up by x4 and you get .... 3400fps with +/- 20fps and maybe (hehehe) ragged hole at 200 yards?

I've no idea? Do you? :confused:


What is a good 'consistent' (standard) variation at CF type bullet speeds?

I would think +/- 20 fps might be considered quite tidy. ;)


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Oi Sir Guy
Think you are using the statistical term SD in a very loose way...;)
Still need some way of paying you the money I owe you for the rough sex in Hayling loo after Jamie failed to show up

[mikemorton]

Oi Sir Guy
Think you are using the statistical term SD in a very loose way...;)
Still need some way of paying you the money I owe you for the rough sex in Hayling loo after Jamie failed to show up

Er, yeah! :eek:

PS I hope to God Gary C didn't really write that, and his BBS account's been hacked!

[Hunter_zero]

How 'anal' are you? ;) :D

For me, accuracy starts with consistency.

Consistency isn't that simple.

If you are talking about your reloading skills then velocity would be an excellent medium of measurement.

BUT

Not for accuracy of the shot. Take away all environmental factors such as wind, heat, humidity and you still have variances in the bullets.

Each round should be a clone of the next and if it was then there would be no deviation in velocity as long as the rifle remained a constant; for example barrel temperature but how can you accurately measure the speed of the bullet? Certainly not with a chronograph due to intolerance's and inaccuracies.

I guess you could make a set up that would accurately measure bullets speed by way of a high speed camera.

I guess in a hunting situation +/- 100 fps makes little of no difference at standard hunting ranges when shooting a round that produces 1700 ftlb of ME.

John

[flims]

according to what i was reading in 6mmbr and the sierra reloading DVD, 30ft/s of extreme spread is quite good. the Standard deviation should ideally be in single digits. Sometime ago we chronoed Ruag 300Win Mag Match ammo, same as the one fielded to the military snipers and 20 shots had an extreme spread of 80ft/s. I would have imagined this to be less with such ammo but it might be that this kind of powder offers the most reliable and consistant burn rate immaterial what the temperature is, and for the military applications this is more important than having an ES of 30ft/s. the less your ES the less your group should string vertically. I still saw some realy good groups at 600m however if this round was pushed to 1100m, the ES of 80ft/s might start to show up. For human size targets however it is not a problem. i'de like to run some of those rounds on a neco gauge to check for the mean runout on the loaded rounds.

[RichardH]

Geoff

You're worrying about nothing chief;)

Load five cartidges tomorrow, pick your favoured charge then load one 1 grain light, 1 half a grain light, 1 at your favoured charge, 1 half a grain hot and one a whole grain hot.

Then shoot a five shot group at 100 yards.

What should the group look like?
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Well?
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Assuming the load grouped to begin with you'll have a comparable group of 1/2" or so in a neat circle rather than the neat string you first thought of.

In short if you aren't shooting 600+ yards standard deviation will only confuse you.

Try it;)

Richard (Happily throwing charges straight from a Dillon volume measure)

[Baldie]

Oi Sir Guy
Think you are using the statistical term SD in a very loose way...;)

You are (surprisingly :p) correct. ;) :D Been back and had another look at the 'function' and realised I'm looking for (total) variation /2 to give a +/- figure. Corrected figures (that don't involve square root) aren't so exciting. :( That said, one of Foxshooters loads tried in my gun gave a total variance of 32fps over a 5 shot group. Giving +/- figure of 16fps. Which IS impressive.

Still need some way of paying you the money I owe you for the rough sex in Hayling loo after Jamie failed to show up

At last, confirmation after years of getting it for free, IT IS worth paying for. ;) :D Will be in touch.





Consistency isn't that simple.

If you are talking about your reloading skills then velocity would be an excellent medium of measurement.

BUT

Not for accuracy of the shot. Take away all environmental factors such as wind, heat, humidity and you still have variances in the bullets.

Bullet weights are next. [Sorting by weight possibly.]

I can't control weather or wind. I'm looking to manage internal ballistics because I can. I'll worry about the external ballistics when I've worked out the best I can achieve internally first. :cool:





according to what i was reading in 6mmbr and the sierra reloading DVD, 30ft/s of extreme spread is quite good. the Standard deviation should ideally be in single digits.

Thanks for the 'benchmark' figure. :cool:





Geoff

You're worrying about nothing chief;)

Load five cartidges tomorrow, pick your favoured charge then load one 1 grain light, 1 half a grain light, 1 at your favoured charge, 1 half a grain hot and one a whole grain hot.

Then shoot a five shot group at 100 yards.

What should the group look like?


Mr Lucan, (or should I still refer to you as "Lord"? :D)


I'm trying to work out a method of accurising my shooting in a methodical and reliable way. As has been pointed out above, external ballistic are affected by temp/humity/wind. I'm doing pretty much what you suggest anyway, but I'm using a different method to measure success vs failure.

If I produce a load that gives me "0" variation of bullet speed over a 10 shot group, the downrange 'shotgun strike pattern' will tell me there's nothing wrong with my reloading at least. Whereas I might be tempted to think the load is rubbish? <which is pretty much the story to date>


I'm looking to get sub 2" groups at 200/250 yards, from a 'factory stick'. (As Messrs Ackley would say.)

Once I've got a stable load, I'll be looking to 'tune' the performance with bullet seating depth, and maybe use a sound mod to dampen barrel harmonics if necessary. [Or use one of a selection of sound mods to produce a satisfactory result.] M'lud ....... ;) :D



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[Hunter_zero]

Bullet weights are next. [Sorting by weight possibly.]

I can't control weather or wind. I'm looking to manage internal ballistics because I can.

It's not just bullet weight! Centrifugal balance of each bullet plays a major part, okay a good bullet from a good manufacturer should restrict this issue but the error is still there. You can not control internal ballistics as much as you want. The barrel of you rifle will heat up at different rates, when metal heats it distorts as such there will always be an error. In a nut shell it is all these "little" errors that we can not control that makes it almost impossible to have 100% shot to shot consistency or round to round cloning. That's not to mention errors in scales. Cases necks are not concentric. Case volumes are not the same. Case expansion isn't the same for all cases and rifle chamber heat will effect this also.

All said and done, if you can group your rounds close to MOA or better your doing fine.

I spent a whole summer perfecting a .223 load, messing with cases and all sorts. Final grouping was one hole groups at 50 yds, slightly bigger at 100 yds, clover at 200 yds but at 300 yds the groups opened over 6". To achieve this I had to change the rifle stock, trigger, barrel and have the barrel crowned! After all that the bullets became unstable at around 250 yds. I swapped for a different bullet and then more but could not achieve much better results. At the end of the summer and after spending ££££ on the rifle I compared the original groups of .7" to .3" (after mods and load development) at 100 yds and decided I was chasing rainbows. I sold the rifle at a major loss and moved on to another .243" which achieved .6" groups out of the box with the first lot of ammo I reloaded. The chronograph showed the ammo to be deer legal and I have stuck with the rifle/ammo ever since.

John

[Baldie]

I spent a whole summer perfecting a .223 load, messing with cases and all sorts. Final grouping was one hole groups at 50 yds, slightly bigger at 100 yds, clover at 200 yds but at 300 yds the groups opened over 6". To achieve this I had to change the rifle stock, trigger, barrel and have the barrel crowned! After all that the bullets became unstable at around 250 yds. I swapped for a different bullet and then more but could not achieve much better results. At the end of the summer and after spending ££££ on the rifle I compared the original groups of .7" to .3" (after mods and load development) at 100 yds and decided I was chasing rainbows. I sold the rifle at a major loss and moved on to another .243" which achieved .6" groups out of the box with the first lot of ammo I reloaded. The chronograph showed the ammo to be deer legal and I have stuck with the rifle/ammo ever since.

John

I hear what you're saying. (Or writing - as it were.....)

As you know, there are 223's being used to move 75 grain bullets onto targets at 600 yards. I'm not looking to do this, but I'm going to be gutted if I can't get reasonable accuracy at 300 yards. I'll have some idea by this time next week....... ;)

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[foxshooter]

For some reason loads with a low SD arent always the most accurate :confused:

I've had accurate loads with a high SD and crap ones with single figures. Maybe I just need to tweak the seating depth etc on the low SD loads to improve them....... I dont know

The load I gave you to try on Sat shoots well in mine, if I'd have warmed the barrel I'd have the tankard instead of Tommo :rolleyes: :D Even with the flyer it still shot under the inch. Last time I tried it out I had 15 rounds in a ragged hole, still have the target as I've never shot so well :o

Mark

[Baldie]

For some reason loads with a low SD arent always the most accurate :confused:

I get this. ;)

But I'd say most shooters would expect better downrange performance from bullets traveling at the same speed, than those travelling at different speeds?

The load I gave you to try on Sat shoots well in mine, if I'd have warmed the barrel I'd have the tankard instead of Tommo :rolleyes: :D Even with the flyer it still shot under the inch. Last time I tried it out I had 15 rounds in a ragged hole, still have the target as I've never shot so well :o

Mark


My notes didn't say which brass you had used BTW? <subtle hint?>

Performance of your ammunition was better than ANYTHING I made. I'm putting that down to the quality of the bullets at the moment, since I haven't measured weight variation in either the A-Max or V-Max, though I read someone the V-Max has horrendous variation.

I'm not surprised about the 'ragged hole' comment either. Total (measured) variation with 5 rounds out of my gun; 32fps. Impressive. That's +/- 16fps from mean which was 3346fps. I expect you'll be asked what the load was, VERY soon. ;) :D


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[RichardH]

I haven't measured weight variation in either the A-Max or V-Max, though I read someone the V-Max has horrendous variation.
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For what its worth I weighed some 52 A-Max's last week and they were very consistent with a max variation of +/- 0.1g

Bergers in 50 grain were all identical.

CST's in 40 grain suit my triple with groups sub .4" and they vary by a grain each way:D

Richard

[Baldie]

For what its worth I weighed some 52 A-Max's last week and they were very consistent with a max variation of +/- 0.1g

Richard


Someone, somewhere on the rimfire section, said these were the best bullet for the 223 they had ever tried. Maybe they'll try the Bergers if they read this? :D

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[RichardH]

Someone, somewhere on the rimfire section, said these were the best bullet for the 223 they had ever tried. Maybe they'll try the Bergers if they read this? :D

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Its funny because even though they shoot well I dont use them, the hollowpoint gets damaged too easily for my liking and that cant be good for accuracy.

Richard

[baz]

If you are worrying to this extent I hope you are going to single load your gun as cycling the mag causes enough damage to affect accuracy as the things you are worrying about:D

Unless you are shooting BR I wouldnt worry, but if you are you need to measure each case capacity with a pippete, neck turn, weigh each kernel of powder....;)

Get some good quality cases bullets and primers, suitable powder and get the ogive the best distance from rifling, and go and shoot something:D

[Baldie]

and go and shoot something:D


If I ever get these fooking cases clean, that's EXACTLY what I plan/expect to do. ;) :D

Now, must go.......got some bullets to weigh. :p :D :D