How to get single digit SD ?

Assuming that you get the same amount of powder in each round. What do you think will affect the SD the most, Burn rate, fill volume, black magic ?
I have a load that will shoot less than MOA at 100 yd but the SD is 29. Same gun but different powder and bullet and I get an SD of 6.
5 shot groups loaded with Lyman 1200 auto scales.

An SD of 29 is about a 87 to 116 fps extreme spread. That's a lot! I look at the Extreme Spread (ES) on my ammo. SD is helpful, but I like to see a low ES- generally 20-25 or less is best. A 20-25 fps ES will generally give you about a 6 to 7 SD.

I load my precision ammo to .02 grains consistency on the powder. Having powder charges accurate to .02 grains helps get the powder charge accurate to the kernel. But, the key is consistency. Consistency on everything you are loading. If you are switching head stamps (brands) of brass, they will have different internal case volumes causing different pressures, which will effect your velocity. Make sure you are sizing all the brass the same way.

Also, using stainless steel media has increased ES numbers. The stainless steel media cleans the brass too good, and some of the additives leave a sticky feeling on the brass when you seat a bullet. This sticky feeling causes the bullet to release different and raise ES numbers. I know several comp shooters who stopped using stainless media because of the high ES numbers and having vertical spreads at distance.

There are many different things that will effect the ES. Having the same for everything will help greatly.

First question is quality of chronograph?

Neck tension helped mine a good bit as did minimal sizing.

I used to do just the normal die set up and didn't anneal it wasn't as good. Started only bumping .001-.002 and annealing every 22nd or 3rd firing. After that numbers dropped.

That being said I try to only stick to known temp stable powders. After that I want at minimum a 80% case full volume as I have typically found the best accuracy in the loads closest to or being compressed.

The load is a 6.5 grendel Nosler 120 Spitzer over 25 gr. of IMR 3031. Velocity could be better- Max. 2362 Min. 2290 ES=72 SD 29
The chronograph is a Magneto Speed and it's my first time to use it. But it appears to be simple- Select the correct type of bullet and shoot.

Thanks for the comments I can tell I have more work to do. Normally I clean, size, trim, deburr and chaffer prime and BOOM.

what additives are you speaking of? after I run the steel media, I do a rinse run.

You're running a load at about 38000 psi. Progressive burning powders (which is what all modern smokeless powders are) work best and most consistently at certain pressures where 100% consumption of the powder takes place. You probably won't see 100% burn at 38000 psi, so I would try bumping the charge up some. The higher the pressure is, the more consistent the burn will be.

If you're loading one day and shooting the next, or even within several days, the necks being "too clean" has nothing to do with it. Galvanic bonding will take longer than a few days to form.

Neck tension and ignition are two places I focus when attempting to lower ES/SD. Primer brand change can significantly change those numbers too.

I do agree with Chad on brass necks with no carbon are a killer...you have to use some neck lube and it be consistent for it to do the same work as the carbon build up will.

This "too clean" theory is bothering me. Why can a stellar load be made on virgin brass?

I get that carbon slicks up the inside of the neck, but go back to the virgin brass question.

red bluff,

As these guys have stated, I do what they do.

-Flashole debur
-Bushing FL die with a .002" shoulder bump
-Trim, chamfer, debur
-Good primers, CCI and Federal
-Temp stable powders loaded to .1 gr (don't have the equipment to get any finer)
-I tend to load on the high node, that shot best giving as much case fill as possible before pressure signs
-Seat the bullet in relation to the lands, completely ignoring SAAMI O.A.L. I start all loads even with the lands to .003" jump as long as it fits in the Mag
-In hot weather, keep the ammo out of direct sun as much as possible

One other thing, certain cases lend themselves to very low ES, and SD better than others, often due to case geometry.

My .260 Rem had an ES of 18-ish, my 6.5 Creedmoor has an ES of 13-ish. I think Chad and Dave have an ES of 10 or less on 6.5 X 47 Lapua. Judd has some BR cartridges that have single digit ES as well, if memory serves.

I get single from my 6mm creed and haven't checked the 7 Ackley with good brass. It had 10 with bad brass that was on it's way out.

I have asked ammo manufacturers about cold-welding and what they do about it. The responses I have received suggest they believe there is no issue to address.

There was a thread a while back where Chad was talking about powders for .223, and he happened to mention AR-Comp as being a very good powder. I took a look at the data and decided to try it. It has given me the most consistent velocities I have ever seen in .223 Remington (running 50-grain Ballistic Tips), and SDs for five shots are often less than 10, and sometimes less than 5. I had used a number of other powders over the years and obtained decent accuracy, but never such consistent velocity. Charges were thrown with the Chargemaster (AR-Comp's one downfall is poor metering through a measure, it is extruded and has rather long kernels) and no other special care was taken...BUT my brass had been annealed and I think was on second subsequent firing. Also, brass had been tumbled to "like new" in stainless media.

I've seen Judd finish seating bullets, at the range, with an arbor press, just before shooting them. Being a Bench-Rester he worries about things. I don't chrono my ammo every time I shoot it, so I can't say one way or another if ammo I loaded last month, or a year ago, shoots any worse than ammo I loaded yesterday. But I'm not punching paper for groups either.

Chad pointed me to IMR-8208 for the LR-308, and 155 gr bullets. It was the ticket! I knew I was going to be hurting for velocity, as well as a low ES on a mass produced 16" AR in .308 Win. But if memory serves, the ES ended up in the low twenties, and it did produce the velocity I was hoping to get. So one other thing to get the ES and SD down is picking the most appropriate powder for the chore.

One thing that has occurred to me is that some guys may have that unfortunate condition where everything they touch will rust. One of my buddies has to carefully wipe all his fingerprints off any firearm he handles because those fingerprints tend to become a permanent part of the finish. I suppose it's possible that when handling bullets, the same thing could happen where the acids in their fingerprints accelerate the cold weld process. That could be why the factories don't see cold weld as an issue---minimal human contact with the brass and bullets, maybe?

Plausible

^^^ This is the key.

Red Bluff, On your 6.5 Grendel with imr 3031, I'm not even showing load data for 3031. So I ran your data through QuickLoad, and it shows a 38K psi load. The Grendel is rated at ~52K psi. Ammo gets more efficient when you run a full pressure load. As you dial the load down, you make it more inefficient. If you do dial the load down, you need to run a faster burning powder to make up for this difference and get the pressures up near max. I don't have any load data on that imr 3031 for your application. If you look at the reloading data, notice the powder charges and burn rates of those recommended powder charges with the 120 grain bullets. You will see the powders are much slower burning than the 3031. This will help make the round more efficient and lower your ES.

I have guys call me and ask what 1 powder will work in ALL their calibers. Most of the time there is not 1 perfect powder for multiple calibers without sacrificing performance on one or more of them. You have to select the right powder for not only the cartridge you are shooting, but the bullet weight also. For your Grendel, anything in the 8208, TAC, H335 area will work best with a 120 grain bullet.

Honestly, I'm not 100% sure, but here's what I know. The issue with SS media is it gets the brass too clean. Like Jeff mentioned, it removes all the carbon build up in the case neck. Yes, virgin brass is the same. But I think the SS media effects the neck differently. It may matte the neck up some, or leave a chemical residue from the cleaning process. But I have loaded on brass cleaned with SS media, and it is definitely more "sticky" when you seat a bullet. I think this stickiness causes the problem, like the cold-welding issue. But that's my opinion, and I admit I have no proof. I have never used SS media personally, because of the multiple shooters I know going away from it. But I do know multiple competition shooters who ran it, and had high ES numbers and had issues with vertical spread at 1000 yards. Would your normal hunter notice this shooting a deer at 100 yards, probably not. But for the precision shooter, I think so. And my walnut and corn cobb media has never let me down, so that's what I use.

So for the SS folks would you advocate a dry neck lube prior to seating? Graphite? Mica?

I only SS clean my pistol and .223 brass. Other stuff gets wiped off with a diluted Ballistol before lubing and sizing or tumbled in walnut/corn cob if really dirty.

Chad, I doubt this but are there any long range competitors running factory ammo? I think this is fertile ground for a well designed scientific investigation in any case, no pun intended.

There have been some guys running 6.5 Creedmoor, Hornady Match in the past. But I know that was when Hornady was loading it with 42.0 gr of H-4350. When all of us couldn't get powder, Hornady changed the powder they were using. Performance suffered, and people got ticked about it. There were threads on which ammo lot to avoid.

The percentage of competitors running mass produced ammo may be in the single digits. The requirements of the ammo are just too tight, more so than they were 5 years ago.

The new Hornady stuff is a blend and almost impossible to get the same velocity as factory. When ran on the magneto it had a sd in the teens. Once we adjusted for bc it was pretty consistent.

I have seen some Hornady sponsored shooters run the factory 6.5 CM ammo. Several years ago I saw the factory ammo perform well, with a cold bore shot at a 1000 yards on the first round of the morning in a competition. I have also seen several LEO departments run factory FGMM in 308 since that's what they are issued. Some have finished top 10 with 168 SMK FGMM.

Most shooters do load their own, since that's where the accuracy and consistency is found.

I have noticed too after SS tumbling brass it does become sticky if you do not rense it off afterward. I run by brass through clean water afterward. It does not feel sticky to the touch once it's dried. I do use graphite to lube the case necks before seating though. I have not noticed any changes in my ES after using the SS tumbler.

I've noticed that as well. I only use Dawn and Lemishine, and thoroughly rinse afterward. Then lay out a bath towel, pluck a piece of brass out, and put a ball needle, on the blower, attached to the air compressor, through the flash hole. I blow out all the water, and lay the brass on the towel. I put them in rows, and when I get to the last piece of brass I fold the towel over and roll the brass drying the outside. From there it is directly to the annealer, which removes any further moisture. This is my process after two firings.

I get single digit ES with my RUM, and clean with SS media, but I only use distilled water with a little white vinegar and throughly rinse after.

I should go to distilled. Can't believe I forgot that!

You probably don't get any water spots on the brass, I would think.

on the distilled. I use it mostly but bottled water/1 gal jug works well too.

Free distilled water from my dehumidifier.

I'm using softened water and always rinse the cases well with the cold water. I have not noticed any residue of any kind, and no sticky feeling. I have RO filtered water available but never thought to use it, no apparent need.

That's actually not a bad idea. Though is it truly distilled after condensing on a metal heat exchanger? Or would you assume it would have wild ions diluted within it?