SD vs Accuracy

[Walt]

In the Wolfe Publishing online article that came out yesterday there was an interesting story on test-firing a Smith .45 Colt from a Ransom Rest with various loads. What I thought was most intriguing was the relationship between standard deviation and accuracy. Lowest SD is not an absolute indicator of best accuracy but it suggests that a relatively low SD, such as between about 5 and 15fps seems to do the best.

[Scott Tschirhart]

It makes sense that lower SDs would lead to better accuracy. But I am not convinced that there is a direct correlation, particularly at typical handgun ranges.

[AJMD429]

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Consistency in as many factors as possible would usually be key to hitting the same place repeatedly.

I've seen many expert reloaders try 'refuting' things like weighing powder charges, neck reaming, precision seating, and so on, and it is always interesting.

One of my most accurate loads/rifles was 6mm Remington, loaded with the 'Target' version of the little Lee Loader kit, with inside neck reamer and micrometer seating. However with IMR 4831, I could just 'dip' the cases in a cereal-bowl of powder, shake the case enough to get powder out of the neck area of the case, and finish loading the round the usual way, and still get 9 or 10 shots in a dime-sized group at 100 yards. So for that load and gun (Ruger M77V), no precision at all was needed in terms of powder charges. My thinking is that perhaps the very slow powder simply didn't completely burn while the bullet was in the barrel (there was always a big muzzle fire-ball), and 'metered' by barrel-length, the excess simply making a variation in the fire-ball.

[Scott Tschirhart]

I’ve had loads that varied quite a bit that shot very well. Then again, I’ve had loads that should shoot well that didn’t.

There may be more at work than we think.

Many years ago I had a Remington 600 that shot lights out with cheap red box Federal 150 gr .308 soft point. No other factory ammo would do as well. No handload I tried would do as well.

But it liked that load.

These days I shoot .308 Remington factory 150 gr Coreloct and I don’t worry too much about groups and I don’t bother loading.

[AJMD429]

These days I shoot .308 Remington factory 150 gr Coreloct and I don’t worry too much about groups and I don’t bother loading.

No matter how much I practice, unless I'm at a bench with a rested long gun, MY inaccuracy is going to be way more than the gun's inaccuracy.

So although I do try to find a 'good' load (reload or factory load) for a given firearm, what I elect to use for ammo is more based on the bullet construction and 'reasonable' accuracy than it is on anything else. Having a hunting or protection gun that I'm trying to get to shoot 1/2" vs 1" groups with at 100 yards may be 'fun', but it just isn't realistically practical - unless I'm shooting from a padded rest while hunting deer or protecting the home, my inherent abilities are going to limit my practical accuracy of fire to at best maybe 4" at 100 yards, and that will do. If it's with a handgun, I don't think "minutes of angle" wouldeven be the right term - four inches at four yards is probably 'enough' accuracy for the rapid-response world of self-defense, and the best I'll get in that kind of shooting - that would be 100 inches at 100 yards for 'accuracy'...100 minutes-of-angle...

[Keith D]

Some bullet shapes just shoot better than others. Makes sense that wadcutters are no good at long range...no matter the SD.

[Walt]

It just doesn't make sense that in these tests where the hold on the gun, the aiming technique and the trigger pull were mechanically made consistent, would have extreme spreads in the most accurate loads of sometimes 60 or 70fps. Is it differences in bullet composition, is it harmonics, is it barrel temperature variations? It's a puzzling business and that's what keeps us coming back.

It's kinda like Taffin's Perfect Packin Pistol. There's no such thing but the search for it is the attraction.

[marlinman93]

I've always felt that the lowest SD I could get from my hand loads for rifle or pistol will always result in the tightest groups. Velocity in general means less to accuracy, unless the velocity also gives tighter SD readings.

[Scott Tschirhart]

Over the past couple of days I have been shooting a variety of guns with two loads.

6 gr Red Dot 250 gr RNFP for about 800 fps or a little better. This is a remarkably consistent load with very low SDs

8 gr 231 250 gr RNFP for a bit over 900 fps. This one is much more volatile. Sometimes I’ll have three that are very close together and one or two will vary quite a bit.

But, at 50 yards there is no contest. The 231 load is more accurate in each gun.

[TedH]

In my experience the benefit of low SD really only comes into play at longer rifle ranges where vertical dispersion is evident by large velocity swings. I have favorite rifle loads with SD in the 20's that are more accurate at 100 yards than a different charge that has a single digit SD. With handguns I don't worry about SD at all if its an accurate load. The two don't necessarily go hand in hand.

[GunnyMack]

I never bothered to check SD while trying to find a load for my small ring Mauser in 257AI. No matter what bullet, powder, primer combo I tried in the past 30 odd years nothing would shoot under an inch. However just about any load would come together at 200. Somewhere I was told about a theory called bullet going to sleep. In short it means said bullet needs to settle down after its travel down the bore and after X time of flight it finds itself and accuracy comes in.
Yes I did finally find a bullet,powder combo that gives me about 5/8" 3 shot groups at 100.

[Scott Tschirhart]

I never bothered to check SD while trying to find a load for my small ring Mauser in 257AI. No matter what bullet, powder, primer combo I tried in the past 30 odd years nothing would shoot under an inch. However just about any load would come together at 200. Somewhere I was told about a theory called bullet going to sleep. In short it means said bullet needs to settle down after its travel down the bore and after X time of flight it finds itself and accuracy comes in.
Yes I did finally find a bullet,powder combo that gives me about 5/8" 3 shot groups at 100.

I’ve read about this bullets going to sleep thing. But I never witnessed it.

It may be like the arrows I used to shoot. They had to straighten out in flight.

[Griff]

I got my .40-90SBN Shiloh Sharps in 1987. I'd purchased 45 Basic brass, dies and a couple of molds before hand, but waited until I got the rifle to load any ammo. I had a mixture of CSA, HDS and unmarked cases all formed and ready to load when the rifle arrived. I got the rifle mainly to hunt with, but also wanted to shoot it in the long range side match at EOT in SoCal. I had about a month with the rifle before the match in Apr of '87. I'd talked quite a bit with Mike Venturino while the rifle was being built about loads what to expect. BP wasn't much of a mystery, fill the case to the base of neck and seat a grease groove bullet. (The rifle was ordered without the chamber being specified, as I hadn't ever experimented with paper patching)! Mike V. had given me a 100 smooth .400 diameter 375 bullets to learn how to paper patch with... Failure! Shiloh called before the barrel went to get bored and chambered to confirm what I wanted. At the time I had 2 molds, a 370 grain WFN from LBT & a 350 grain mold. The rifle was their Long Range Express model with the barrel cut to 30" in an attempt to keep weight below the NRA allowed 12.3 lbs. As received, with no rear barrel dovetail, Shiloh's mid range tang & globe front sight, it weighed exactly 12.1 lbs. The range at Coto de Caza where EOT was held was limited to about 225 yards. The public range where I shot had 100, 200, 300, 400 & 500 yards rifle positions, but I did most of my pre-match testing at 100 & 200 yards. I could keep 10 shots with the 370 LBT bullet inside the 7 ring at 100 yards, and inside the 9 ring at 200, with an occasional flyer I mostly attributed to me. The rifling is a 18:1 twist, suitable for the mid to lighter bullets I was using. For the upcoming EOT I initially tested using Accurate's 5744 as the propellant. Mike had advised me to keep charge weights to about .45-70 levels. I don't think I ever bettered 5" 5 shot groups at 200 yards. The side match at EOT is scored by most hits on the buffalo target with time being the tie breaker. As I recall, a 10 shot string. I hit all ten, but the Sharps isn't a quick action rifle, especially when I lacked much experience with it. I wasn't in the running for winning. Shots were taken from seated on the back of a "horse", (oil drum mounted on pipe legs). But, unlike the previous year they'd removed the "rockers" from the horse, so at least it was stationary. At the time I didn't own a chronograph, so never knew my SD & ES numbers. But, the rifle performed better with black than smokeless. So, for the match I was using BP loads. A couple of years later a friend got a Chrony and I finally got numbers. 85 grains of 2F chrono'd around 1590 fps. I tested some Pyrodex and velocities climbed to 1690fps. Mike V. chewed my kiester! I tried compressed loads and uncompressed; compressed loads didn't like the target, they wandered all over. I switched to GOEX "Cartridge" BP when it was introduced. The GOEX representative told me that Cartridge was a blended ffg-f-½g with increased graphite coating over their regular sporting BP powders. My SD & ES numbers came down, but accuracy never really got better. Every year or so I get the rifle out of the safe and play with it some. I'd love to take it hunting with the plan to actually use it, but I've never gained any confidence in it's 100 yard performance. At 300 I can keep on the pigs, & usually get 8 of the ten rams at 500 meters. In the early '90s Mike gave me a 400 grain mold he'd used in his .40-70, but the .40-90 didn't care for it at all. I should really cast up a bunch more of the 330 grain RCBS

[marlinman93]

In my experience the benefit of low SD really only comes into play at longer rifle ranges where vertical dispersion is evident by large velocity swings. I have favorite rifle loads with SD in the 20's that are more accurate at 100 yards than a different charge that has a single digit SD. With handguns I don't worry about SD at all if its an accurate load. The two don't necessarily go hand in hand.

I agree that for handguns there are lots of things I don't spend much if any time on. At the usual handgun distances it just isn't time worth worrying about for me.

[piller]

I have only tested a handful of loads for velocity and consistency. One 30-06 load that worked great in cold weather with some 100 yard groups all 5 shots touching was only fired one time in the summer. 1 round and it was darn near impossible to work the bolt. I got it out, unloaded the gun, and marked them for shooting in freezing weather only. That Remington never has seemed the worse for that 1 time. I rented a go/no go gauge from the range. I micrometer measured the brass. Nothing seemed wrong. I opened 3 cartridges, and the charge was in what should have been safe weight territory. I finally shot the remaining cartridges in 30 degree weather. Great accuracy, but I never loaded that exact charge again. Puzzling, but they were pretty stinking accurate at 100 yards and 30° outside temperature. 105° was scary. I just don't know. I do reload for a few different cartridges. I only have a single stage press, and weigh every charge until I get 10 throws in a row to all be accurate on my Lee balance scale. Then it is every tenth throw checked. On some cartridges which the pressure is being held much lower than SAAMI limits, I am not so precise. For example, .357 cartridges in .38 special +P power territory. I have quite a bit of room to be a bit sloppy with as long as there are no loads which are too light and could detonate, and no overloads. Checking with a flashlight for uniformity before bullet addition and seating is always done. Those batches do not give me any indication that accuracy is different from precision weighed charges. Maybe I am not good enough to tell.

[wvfarrier]

I do not chase SD/ES numbers, I chase accuracy. My normal ELR load for 308 has double digit SD's but will shoot half moa out to 1000 yards.