How do I get single digit ES/SD?

D

diegocn

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I just tested some load last week for my new 308 barrel. While the group is decent (0.8 moa at 100 yard), I was not happy with the ES/SD spread. Here are the measured data:

Speed (fps)
2632
2633
2594
2608
2578

Mean: 2609 fps
Std Dev: 21.41
ES: 55 fps

My current process is:
- Remington 308 brass, full length sized through RCBS dies, trimmed to 2.005", but no annealing or other special preps.
- CCI #200 primer
- Powder charge of Varget should be within 0.05 grain of the target weight
- Decent bullet (Nosler ballistic tip 168gr) with consistent seating depth that's 0.010" off jam
- Rifle is a Savage 10 with IBI 308 barrel in a Savage Accustock.
- Chronograph is a shooting chrony F1

I'm wondering what's the most effective improvement I can make to my process to cut down ES?
 
Buy better brass. Norma,Lapua and such.
Lee Collet dies.
Did this on my 25-06 and the change was huge.
Was down to single digit.
Or sort your brass by weight.
Lee Factory crimp die has also brought down ES/SD on every rifle I own
My 2 cents
 
0.8" groups is not very good and I doubt lower ES is going to save the day for you, but its worth a try.

There are so many things that contribute to both accuracy and velocity, all you can really do is go after them one at a time.

You state your powder charge is within 0.05 grains... based upon what? I have encountered only a few people would can actually maintain such a weight spread. I can because I have an analytical balance, but if you're using something like an FX120 scale you are probably more along the line of +-0.04 grains for a total weight spread of 0.08 grains.

One thing I can suggest is that you examine your neck and throat. A sloppy neck and sloppy freebore diameter will alow the bullet to strat into the rifling at random angles. The more random the angle, the more variability there will be on the force required to get the bullet moving.

If you can run a tight neck, you can use that to better ensure the bullet starts into the rifling straight and that will lower your velocity spreads.

The next thing is to focus on the weight of your brass. During load development at least, make sure you use cases that are as close as possible in weight.

Also use fire formed brass not full length resized brass. If you have a neck only die, then use that. (at least during load development)

Pay close attention to your neck tension and the quality of chamfer on the neck. If you are shaving bullets when seating, you need to improve the quality of the chamfer... even polish the chamfer with like 240 grit paper just a bit.

Another consideration is cold welding where you dont want your loaded rounds to sit for a long time after loading before your shoot them. F Class guys will seat the ammo too long then on day of event, they will re-seat to correct depth.
 
The strongest and most certain answer is to switch to a better designed and more inherently accurate and low SD cartridge, like 6 BRA.
 
there is a long list of things you can do, which require spending a lot of money if you're not already set up for it, so the simplest easiest thing for you to do right now that costs nothing is this......

deburr the flash holes and uniform your primer pockets
sort your bullets by overall length and base to ogive
try different brands of primers
trim all your brass to the same OAL
chamfer and deburr case necks

single digit loads can also be the worse shooting loads in your rifle, if you're happy with the target then run that load and have fun, set your mind at ease by running a ballistics app with your fastest and slowest muzzle velocity and see what the actual results are down range at distance, are you good enough at reading the environmental conditions to shoot better then that difference? Some computer nerd with no shooting experience came up with the theory that single digit es and sd are must haves.........it's nice, but it don't mean S$1T
 
diegocn said:
I just tested some load last week for my new 308 barrel. While the group is decent (0.8 moa at 100 yard), I was not happy with the ES/SD spread. Here are the measured data:

Speed (fps)
2632
2633
2594
2608
2578

Mean: 2609 fps
Std Dev: 21.41
ES: 55 fps

My current process is:
- Remington 308 brass, full length sized through RCBS dies, trimmed to 2.005", but no annealing or other special preps.
- CCI #200 primer
- Powder charge of Varget should be within 0.05 grain of the target weight
- Decent bullet (Nosler ballistic tip 168gr) with consistent seating depth that's 0.010" off jam
- Rifle is a Savage 10 with IBI 308 barrel in a Savage Accustock.
- Chronograph is a shooting chrony F1

I'm wondering what's the most effective improvement I can make to my process to cut down ES?
Click to expand...

You already have an aftermarket barrell, but there are many things you can do to cut down ES, most of which entail spending money. I would first ask myself how much accuracy I need for the task at hand. Despite Maples comments, An honest to goodness .8 MOA (not cherry picked but every time) that stays that way at distance is fine to start off in ORA Precision Rifle for example. Have you shot it further than 100 yards?
Better brass ditching the resizing button in the sizing die and buying a mandrel die may be a place to start.
YODAVE also offers some pretty sound advice
 
Sorting bullets and brass into batches that are similar will help .
Good job .
Sounds like a shooter, chase those lands..

Having little jump will help also.
Dosent change your C-1 Internal capacity during ignition
 
First off, get a better chronograph... or better yet, don't bother chasing ES/SD

Work up your load with properly prepped brass, powder charge AND a true match bullet at 200 or better, 300yds. The target will tell you all that you need to know about how your load development is working.

When it shoots into itty bitty groups, you have resolved the ES/SD question.

If you are running a foldy bipod, change to sandbags or a pedestal rest of decent quality. If off a wobbly bench, consider shooting prone. if you are running a cheap, low mag scope, consider a quality high mag scope to confirm how the aiming is going.

have you properly bedded the action and stock? Accustock sounds good on paper... not so good in the real world

Then of course, there is the shooter question. If you have been able to consistently shoot itty bitty groups, then sorting out the ammo will get the rifle shooting well with testing.

Shooting itty bitty groups is a system and process... ES/SD is the end result of ALL the other work that goes into making an accurate platform, not the start

And often, the most accurate LR loads DO NOT have single digit ES/SDs

Jerry
 
Realistically I would love to have single digit ES's.

I do get a string (10 shots) occasionally in the single digits, but mostly they are ~ 15 ft/s

Loads are chrono graphed on nearly every shot, with a LabRadar.

My loading regime is pretty well set, so results are fairly good.

What I do find is while practicing bench technique, the hold will make the ES drift if the hold is not consistent.

Anneal or at least stress relieve the cartridge shoulder neck area, leave the carbon inside the neck , sort case volumes , insure the case is sized correctly also helps in holding the 'jump' consistently as are items others have stated.
 
You're trying to get single digit spreads with a chronograph that is only rated for 99.5% accuracy. (and that's pretty optimistic) That's plus or minus 13 fps at your velocity.

See the problem? You could have zero spread and still show a 26 fps extreme spread. Or you could rattle off a string that met your goal and it wouldn't prove a thing.

I think there should be a competition where everyone mails in their chronograph print-outs, detailed records of their case, powder and primer weights on a certified lab-scale and naturally they would need to some standard method of determining cartridge runout, and everyone would need to show the measured seating pressure on each cartridge. They could run everything through a computer algorithm and mail out the medals and nobody would even have to travel to shoot and get beat by "lesser" ammo. ;)

Shooting just confuses thing.
 
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diegocn,

A 0.8 group is great for hunting. within the distances you are going to shoot, such ES and SD will not make much of a difference.

Now if you want to be a perfectionist I would suggest the following. You will need to have good brass of similar weight and trimmed to the same length and preferably full length sized with a 2 thousands bump, or neck sized. Proceed with a ladder test. This means load 1 cartridge with powder increments of 0.2 grains. Shoot with a chronograph without worrying for impact or groups at this time. Find your speed node which is a plateau where speed does not change much over 2 or 3 consecutive loads. Once you find that speed node, load 3 cartridges with that load and shoot them. Look for group and ES as well as SD. If you are not happy, try a COL +/- 0.005 from your original load. With that you should be very good.
Using this method allowed me to find sub moa each time with some SD of 2-3. I even had a load with a SD of 1. Go figure.
 
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Since you already have the Barrel, start with the 3"B's"...Bedding, Brass and Bullets. Bed the action and make sure the barrel is free floated. Buy yourself some Lapua brass and weight sort it. Try a different bullet and different seating depth, some bullets shoot better with lots of jump. Shoot for accuracy and stop chasing numbers.
 
Good 308 brass is not overly expensive.
Deburr and uniform flash holes.
I don't know how long your barrel is, so I can't recommend going up in your powder charge, but lower can find a node, I run 42.5gr Varget with 168's, and it's very tight ES, 24" barrel, not a hot load.
Vary seating depth, try a bit deeper with a little more jump.
Don't be scared off neck sizing, I have some rifles that only like neck sized loads, FL sized groups are gross in them.
 
Do you know the capability of your Crony? How much of your ES is the load and how much is the chrony?

ES + SD are load consistency issues. Accuracy includes this but also the mechanical dynamics. Consistency in powder charge, brass condition, component variability, seating and especially neck tension would be the areas to focus on- but of course as Gerry says the small groups on the target tells the story not the ES.
 
mimile said:
diegocn,

A 0.8 group is great for hunting. within the distances you are going to shoot, such ES and SD will not make much of a difference.

Now if you want to be a perfectionist I would suggest the following. You will need to have good brass of similar weight and trimmed to the same length and preferably full length sized with a 2 thousands bump, or neck sized. Proceed with a ladder test. This means load 1 cartridge with powder increments of 0.2 grains. Shoot with a chronograph without worrying for impact or groups at this time. Find your speed node which is a plateau where speed does not change much over 2 or 3 consecutive loads. Once you find that speed node, load 3 cartridges with that load and shoot them. Look for group and ES as well as SD. If you are not happy, try a COL +/- 0.005 from your original load. With that you should be very good.
Using this method allowed me to find sub moa each time with some SD of 2-3. I even had a load with a SD of 1. Go figure.
Click to expand...

Funny that you mentioned this, because that's the entire reason I started chasing ES/SD. It's not to chase accuracy but rather use the 10 shots load development process. The 10 shots load development process is described by the 6.5guys here: http://www.65guys.com/10-round-load-development-ladder-test/

This is the fps vs powder charge for my rifle using this method:
voGiLQd.png


From here I selected the middle of my node at 45 grain of Varget. Loaded 5 more and to my disappointment the fps can go as high as what 45.4~45.6 gr will achieve. The group is still respectable for hunting but I start to question whether the plateau I see in the data is a true plateau or just coincidence caused by large variation in fps.

I really like the idea of the 10 shots load development process as this saves tons of time and components. However I question the meaningfulness of this method if I cannot get consistent fps from my loads. TBH I think the group I had there is as good as picking a random powder charge and load 5 rounds.

The rifle is setup as a lightweight hunting rifle, with 16" barrel and the group was shot with a leupold ultralight 2-7x28mm scope at 7x power. The group is definitely usable for hunting up to 300 yard, and with 55 ES the drop difference at 300 yard is less than 1" anyway. After that I won't be able to hold over consistently with the tiny scope anyway.


It sounds like the answer so far is:
- Better brass
- Deburr flash hole and case mouth
- Neck sizing + 0.002" shoulder bump
- Brass and bullet sorting
- Better chronograph

Before the posted I was wondering if annealing would make a big improvement, and plan on sending some brass to a friend to anneal. Sounds like that's not an issue.

I think I'll get started with some lapua brass and lee collet die (friend has them so no cost to try). Currently I use small base sizing die on all my hunting ammo for reliability, probably should stop doing that too?
 
ES and SD as well as group size can be tuned with bullet seating, there is no 10 round short cut to reloading the perfect recipe, if it was that easy shooting would get boring really fast
 
If your groups are tight, ES/SD are tight.

I would be much more worried about finding the harmonics sweet spot, than ES/SD

As for neck turning, remove as little brass as possible, to keep neck tensions consistent. That's the only advantage to turning necks, unless the neck area of your chamber requires turning the case necks, so the necks will fit into the chamber.

If your chamber is a standard SAAMI speck chamber, even on the tight side, there is so much expansion that necks are almost completely taken out of the equation, other than a perception.
 
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Stop chasing velocity. Deburring flash holes is a waste of time IF you buy quality brass. (not to mention potentially dangerous if you don't know what your doing). Eric Cortina and a few others on utube cover this in depth. Let the target tell you what your rifle likes. I have watched people burn out barrels and send thousands down range, when the real problem is the nut behind the gun. Small things can make a huge difference in accuracy, that second cup of coffee, panic trigger pulls etc. 10 rounds is far from being a quality control group. Film yourself or have a friend watch you shoot then listen to their impute. Eg had a friend at the range he kept pulling the last shot in the string. I watched him for a while took his sling off the rifle, groups improved immediately he was reaching up and torqueing the sling as he came close to that perfect group. Little things, primers etc.
 
diegocn,

If I were you I would try the 45 grains with your COL +/- 0.005. Or go down to 44.1-44.2 and see what happens.
 
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