Secret to get down on Extreme Spread

[GlockTerrier]

I'm relatively new to handloading (by handloading I mean small scale reloading with mostly hand tools and a turret press ). I did experimental loading of .223 being curious if I can make a "better than factory" load. None of case preparation steps and measurements known to reloading masses (except maybe neck turning ) were skipped, charges accurately weighed, match bullets used etc. Results look perfect, shoot better than me midrange, reliable - but clocked velocity spreads are atrocious (ES 50++, SD 30+) and from that point of view they are still much worse loaded than factory ammo I've measured in the same rifle.

I wonder if any of you who reloads rifle ammo for precision was in this position and discovered that by changing one single factor in their practice they significantly reduced ES in their handloads into LR competition range (SD ~= 10 <20)?

(Somehow I have a suspicion that neck tension uniformity may have something to do with this - any ideas what can be done there? )

I've loaded a 2D grid of weighed charges that covered the range from slow, sooty, underpressured rounds to relatively clean and fast, slightly-primer-flattening rounds under the same bullet, seating, uniformed and trimmed case and primers... None was showing remarkably low SD - although SD did vary with the charge it never got into what you'd call "low SD" area... At 100 yards ballistic contribution of velocity SD I'm observing into a vertical group size statistically I'd think is much less than my aimpoint wobble, though

However the fact that factory ammo measures better on SD - bugs me and hurts a budding craftsman's pride Yep, I'm aware of all factors that may contribute to velocity, including lunar phases - I guess I'm wondering if somebody in their reloading experience and practice stumbled upon on some prioritization of the factors that may be involved in consistently higher ES and SD - short of changing basic components...

What kind of ES & SD numbers do you guys get from your own favorites?


Thanks!

 

[silverlance]

sd = sectional density? no, can't be.
oh well i have little idea of what you are talking about. I reload using a big hammer made of dead cow hide and some funny shaped pieces of iron.

 

[Barr]

SD - Standard Deviation

Used to predict variable behavior assuming normal distribution of data under a bell shaped curve.

Avg +/- 2 SD's (denoted by sigma) means that 95% of the predicted results will fall into that range.

Avg +/- 3 SD's means that 99.7% of the predicted results will fall into that range.

Lower standard deviation means tighter spread and the data (shot velocities) are more predictable. Velocity directly impacts time of flight which in turn effects windage and elevation adjustments. The more variation in velocity that is observed, the more variation in your shot group will be observed.

ES - Extreme Spread
ES = Hi - Lo

 

[Barr]

Most of my data is for handguns at 15-20 feet.

Most of my data has SDs of 10-20. I have had some as high as 30-50, but they are not my everyday loads. I have only been chronographing since July of 07. Generally, the trend I have been seeing the most is that it is the powder burn rate that affects the SD the most. I have had the best luck with quick burning powders and the slower magnum powders have been giving me the quirky readings. Your mileage may vary.

 

[birdbustr]

I think your high SD could be attributed to either inconsistent seating depth or you aren't loading the powder consistently. The big thing about consistent bullets is making every component the same every time. The more range, the more important this is.

1. For the seating depth remedy, you can get a bullet comparator from Stoney Point or Hornady. Less than $30. The bullet comparator will measure the bullet length at a specific diameter. If you can make all of your bullets within .003 or so, then the bullets will be a consistent distance from the lands and grooves. Make 2 rounds differ by .1 or so, and you are going to probably some difference in impact.

2. Another consistency maker is of course, a powder measurer and trickler. Enough said on that. $200+ You just can't get really/really good and consistent powder doses without one.

I've got both of these tools and use both. Get the comparator first, it will probably help. When you save up some money get the trickler.

 

[birdbustr]

For pistol ammo, I don't even use anything except a OAL check with a digital caliper every few rounds. I put powder into the cases with the quick powder dispenser and take a measurement every 5-10 to check consistentcy. Short ranges are more tolerant.

I don't think the veriation in crimp is terribly important. As long as your crimp is enough to get a good grip on the bullet it should do fine for pressure. Don't over torque the crimp, which isn't easy to do with a lee factory crimp die.

 

[Barr]

I use a Mitutoyo digital calipers to measure the bullet OAL and an RCBS Uniflow to measure my powder. I set the powder measure and weigh the first few charges. Once the charges start looking repeatable I weigh four charges into the pan and divide the answer by four to find the average. Typically the powder measure is accurate to +/- 0.1 grains which is 1/70,000 of a pound. Most digital scales will have their zero calibration fluctuate 0.1-0.2 grains if a few dozen charges are trickled into their measure pans.

 

[Linear Thinker]

GT, welcome to the board. Your 1st post is far more cerebral and humorous than most. If your "relatively new to handloading" procedure includes neck-turning, I should nominate you for Alfred Nobel's prize. Where would handloading be without him... but I digress.

My formal education was in statistics, but 30 years later I can't tell a bell curve from Poisson's. Still, I will weigh in on Standard Deviation as it relates to bullet velocity. Please keep in mind that the bullet velocity is the only thing being measured by a chronograph. There are lots of other variables at play.
------------------------------------------------------------------------------
Minimizing SD is all about reducing variables. My approach is to break them down:

Is your brass same make, from the same lot? Keep them that way. Keep notes for each batch.
Weigh them, set aside the outliers
Uniform the primer pockets, debur the flash holes
Trim the brass, chamfer the mouth.
Some folks advocate reaming the inside of the neck, and reaming out the donut at the junction of the shoulder and the neck. I have no opinion on this, just passing the advise along.

I never needed the segregate the bullets, all the major makes are very uniform

Must have a good powder measure, I use Jones and Harrell's

I use Lyman M-die to open up the necks
I use bench-rest seating dies, I like Forster and Redding
Crimp the bullets very lightly, I use Lee FCD

I tried concentricity checking of the loaded rounds, but could not correlate it to accuracy.
I tried arbor die sizing and seating, could not see any improvement.

Have fun!
LT

 

[taliv]

i certainly can't point to any one thing, but i also don't obsess about SD.

I've got one load in 6mmXC that once shot a 1" five-shot group at 400 yrds. I consistently get <1" five-shot groups at 200 yrds. When I shot ten rounds over the chrony, I got a 21.8 SD. max was 2881 fps, min was 2804 fps.

I've got two more loads, one with an SD of 11, and another an SD of 12, and I've never shot better than a 1.75" group at 200 yrds with either. They ranged from 2991 to 3022 fps, so a good bit hotter than the previous load.

OTOH, if you're just taking on SD as a personal challenge to see how low you can get, I'd recommend calling the tech support lines for a couple powder companies and ask them what their most consistent powder is for 223. they might make funny faces at you, but you won't be able to see them over the phone.

as for measuring powder, yep, that's important too. I use a harrell culver measure, which is too expensive. I find it doesn't throw nearly as accurately as I'd like. So I trickle the powder by hand after throwing the charge about .2 grains short of my target weight. My trickler is the $5 hornady variety. If I had it to do over, I'd buy the cheapest thrower and trickler I could find, and put all my money in a good electronic scale.

as you mentioned, I'd say neck tension is important, but given the number of other things it could be, it's sort of grasping at straws. if you didn't resize the new brass before loading, SD may shrink a little when you reload that brass, assuming you've got a decent die. if you did resize, and you have a bushing style die (only kind i use for precision ammo) you might try going up or down .001 in bushings and see if that affects it.

edit: i would be interested to hear if you sorted your brass, and if so, based on what criteria?

 

[GlockTerrier]

Thanks, guys, for extending your warm welcome!

Now I also know what to do with this big hammer made of dead cow hide and some funny shaped pieces of iron that my dog found yesterday in a city park...

I really appreciate your constructive feedback that does suggest the answer to my question: this "one thing" may not be there for city slickers

However, your questions and suggestions may already help me to narrow the problem down by excluding some low-probablity factors:

• Brass: once fired LC'07 from the same factory load (Federal AE) that did chrono much more consistent than mine. Didn't really sort it - but random sampling showed what I thought was a small difference within several grains in weight.
• Resizing: Redding FL with nitride neck bushing. (0.244")
• Powder: RCBS Chargemaster 1500 with automatic electronic dispenser/trickler. Works fine, consistent and accurate within 0.1 gr.
• Seating: Redding Competition die with micrometer and with built-in "comparator" (seating setting is done not off the bullet tip)
• Case preparation: Trimmed/squared to the same length, pocket/flash-hole uniformed/deburred, mouth chamfered 22deg/deburred
• Crimp: none. Enough neck tension (0.003") though to hold the bullet in place for most popular tests (pressing the tip, re-chambering with bolt slam in ar15, etc). Can it be ever too much tension, though? What about small amt of case lube inside the rim of neck?
• C.O.A.L - Std Mag length. (2.25")
• Powders used: Varget and IMR4895
• Bullets: Sierra OTH BT MKs
• Primer: "hardened cup" AR15 CCI#41 (ignition is equivalent to CCI "magnum" primers) Wouldn't want to change because of "slam fire" possibilities in Ar15 where the loads are fired.

Looking at all this I think the first thing I may need is maybe to play a bit more with one of the maybe least controllable factors - neck tensions, by trying lighter tension with larger bushing. The theory could be that larger tensions allow for bigger variations in tension and, hence - in pressure. Light crimp (that factory ammo probably uses for semi-auto) then also has a potential to reduce velocity SD by bringing neck tensions closer to each other on a high side of it or to fix the bullet in place when tension gets light... So there could be upside in exploring the effect of lighter tensions..

Primer choice is another worry here... As much as I would like to keep CCI#41 for slam fire prevention I'm now curious if switching it to BR type of primers may have an effect on SD...

What do you think, guys? Well, if I do find what this "one thing" was for me - I do promise to get back and post what it was....

Thanks again!

 

[USSR]

Brass: once fired LC'07 from the same factory load (Federal AE) that did chrono much more consistent than mine. Didn't really sort it - but random sampling showed what I thought was a small difference within several grains in weight.
Resizing: Redding FL with nitride neck bushing. (0.244")
Powder: RCBS Chargemaster 1500 with automatic electronic dispenser/trickler. Works fine, consistent and accurate within 0.1 gr.
Seating: Redding Competition die with micrometer and with built-in "comparator" (seating setting is done not off the bullet tip)
Case preparation: Trimmed/squared to the same length, pocket/flash-hole uniformed/deburred, mouth chamfered 22deg/deburred
Crimp: none. Enough neck tension (0.003") though to hold the bullet in place for most popular tests (pressing the tip, re-chambering with bolt slam in ar15, etc). Can it be ever too much tension, though? What about small amt of case lube inside the rim of neck?
C.O.A.L - Std Mag length. (2.25")
Powders used: Varget and IMR4895
Bullets: Sierra OTH BT MKs
Primer: "hardened cup" AR15 CCI#41 (ignition is equivalent to CCI "magnum" primers) Wouldn't want to change because of "slam fire" possibilities in Ar15 where the loads are fired.

GlockTerrier,

First, let me say that my experience is with LR (1k) competition with larger cartridges, but here is my take on this. You want an ES of no more than 20. To attain this you need to do the following (several of which you don't want to do, due to the platform you are using):

Light (.001 - .0015) neck tension
Change to a milder primer

Going to a light neck tension will help tremendously in lowering your ES and SD numbers. Also, the CCI #41 primer is a magnum primer designed to light the hard to ignite ball powders typically used in military ammo. You are using extruded powders, so go with a milder primer. Another suggestion is to segregate your cases by weight. Hope that helps.

Don

 

[Walkalong]

Neck tension needs to be consistent more than it needs to be light or heavy. That said, it is easier to get consistent neck tension with light neck tension simply because of the math, but we also need sufficient neck tension to keep the bullet in place during feeding in a semi auto like the AR.

Tweaking the neck tension & or the powder charge can make a difference and sometimes we just need to use a different powder. Varget & 4895 are both good powders. I would try H335 or W748 or TAC to see what they do.

 

[taliv]

i'd sort the brass before messing with neck tension. path of least resistance, and all that, you know...

weigh every case

 

[308win]

If you really want to get anal on this instead of weighing cases, uniform them for length and inside neck dimension, fill with water, and measure the weight of the water. Weighing the case is a step to consistency but where is the weight, thicker brass in the - neck, web, etc.? Consistency in volume is what you are after.

 

[BsChoy]

I have read in many places that crimping can reduce SD's but quite a bit...It has mad my Garand shoot real nice.

 

[DWARREN123]

If they shoot good then ES doesn't mean anything.

 

[30Cal]

What's the accuracy on that chronograph? There comes a point where the errors in your measurements become significant.

 

[GlockTerrier]

What's the accuracy on that chronograph? There comes a point where the errors in your measurements become significant.

Very good point!

Yep, Shotting Chrony (that's what it was) has short spaced screens which limits an accuracy and they claim accuracy "better than" <10% which is about <30 fps in 3000fps range in a single measurement. That's why ES can go up as high as 60fps in long enough strings on even ideal loads.

However while averaging over several observations the error relative to average I thnik should drop in reverse proportion to square root of number of measurements and in a string of 10 should be no greater than 10fps contribution into SD and even less on a longer strings... The trouble is the factory ammo consistently clocked SD twice better than mine on the same Chrony... That's why I'm looking for a flaw in the loading process.

 

[GlockTerrier]

If they shoot good then ES doesn't mean anything.

Agreed. ES/SD is just one (and often is not biggest) component in accuracy which represents overall complex effect of interaction of ammo, rifle mechanical properties, bullet aerodynamics and environment.

However, when evaluating ammo manufacturing process I do believe ES/SD is one measurable factor directly related to a quality of ammo construction process on its own. This of course, doesn't guarantee that some particular ammo will be working best in your particular rifle under all conditions abd for all uses - but still, an ammo with low SD/ED is indeed a quality made ammo And making a qualityammo was an initial purpose of handloading for me....

 

[GlockTerrier]

i'd sort the brass before messing with neck tension. path of least resistance, and all that, you know...

weigh every case

Thanks! What tolerances would you recommend for weight variations for consistency?

The problem is this is the same brass from the factory loads that measured twice better SDs! For me this pretty much eliminates the case as a factor of discrepancies..

 

[GlockTerrier]

• Light (.001 - .0015) neck tension
• Change to a milder primer

Thanks, Don! Sounds like a plan!

Will do - and report back...

And, since this is still an AR load the effect of crimping will need to be examined too... I do hope that primer is not a factor and I can get better still with #41...

 

[Howard Roark]

GlockTerrier,

The primer has very much affect on the SD. Try Rem 7.5 or CCI BR4. Both will not slam fire.

I tested Winchester vs Rem 7.5 primers a few years ago and at 300 yards the Winchester vertical stringed a little over 3". The Rem 7.5 shot under 2". 10 shot groups.

I would not go less than .002 on neck tension. There is no way to easily close the bolt on an AR without whacking the case base, moving the bullet.

Sort your brass to 1 grain. I put a line of tape on the bench and write the weights on it and line up the brass behind them as I go through the batch. Patterns will emerge.

A good chrono is a must.

Why load mag length for accuracy? Single shoot. Check your distance to the throat and see if you can jump the bullet only 20 thou or less. SMKs are very forgiving on seat depth. Bergers are not.

My .02
Good Luck

 

[GlockTerrier]

Just wanted to thank those thread contributors who suggested sorting brass by weight to improve velocity consistency.

Limiting resized and unifirmly trimmed .223 brass by weight within 1gr. showed reduction in SD into area of 15 ft/sec in a test-fired string recently. The unsorted brass in the batch had extreme difference in weight of around 3gr and 30-40 ft/s SD

(BTW applying light crimp to sorted brass increased SD by 50% in a separate string - although the difference might not have enough of statistical signifcance yet)

I've also made some calculations using LoadFromDisk software curves for .223 Varget loads under 69gr SMK about theoretical effect of case capacity variations. Here's what I have:

3gr of weight variation in identically sized brass correspond to 1.2% variations in capacity of standard .223 case. These in turn correspond in 605 psi CUP variations in pressure for uncompressed load that in turn translate to approximately +/- 20ft/sec variation. This is a noticeable contribution to velocity ES/SD of competition quality loads. Limiting weight variations to 1gr. brings the effect of the case capaciy variations to negligible 5-6 ft/s.

Limited observation so far and theoretical curves seem to confirm that practice of sorting your brass is indeed a must to get velocity ES/SD lower than factory loads.

Thanks again for all the advice!
Next factors to quantify would be a neck tension effects, primer flash consistency, etc....

Cheers!

 

[Fatelvis]

About ES and SD...... I'm with Dwarren, does the load group well? If you're shooting at <500 yds., don't worry yourself about it! Just practice shooting!