single digit Standard Deviation, what the secret?

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user

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Nov 25, 2009
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#1
Just like so many, I'm measuring each load on an acculab vic 123. Same lot of win 308 brass, varget, cci br primers, micrometer seater, flash holes uniform, and neck tension,,,....only getting SD's in the twenty's is this common with you guys and gals?

Thanks,
 
#3
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BOLTRIPPER</div><div class="ubbcode-body">neck tension and seating depth are also factors</div></div>

And I thought we were going to get a picture of the Prometheus....it's not too late.
 
#6
Re: single digit Standard Deviation, what the secret?

I'm of the opinion that few targets could tell the difference between shots fired with variance in the sd 7 range from those with variance in the sd 15 range.

Still chasing the accuracy demon myself, with an eye to low velocity ES total and sd of the ES. I believe that neck tension and primers are probably the last two things to investigate. Some of my lowest velocity sds were with cases when I was outside turning case necks, and the insides were separately cleaned of residual case lube and were very dry before seating the bullets. This held for both 175s and 155s in .308.

Yeah, charge weights were individually done, and were all within +/- 0.05 grain.

Accuracy on those very low sd loads also sucked in most instances. Maybe my real bag was inconsistent, but we're talking worse than some of my iron sight groups with an M1 Garand in .30-06. Yeah, I'm talking scoped shots here.

I quit turning necks and my "don't clean the necks" loads with weighed charges are grouping better but have sds around 14-20.
 
#8
Re: single digit Standard Deviation, what the secret?

When Marine Corps Rifle Team loaded their own 7.62 they had a requirement of no more than 10 SD on their long range ammo. I know they internally neck reamed cases as I used to pick up their brass.
 
#9
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hummer</div><div class="ubbcode-body">When Marine Corps Rifle Team loaded their own 7.62 they had a requirement of no more than 10 SD on their long range ammo. I know they internally neck reamed cases as I used to pick up their brass. </div></div>
Look it makes sense to internal neck ream. We turn the outside of the neck to fit the chamber and give even neck thickness to assist precisce bullet pull etc. However the inside of the neck might look like a moon surface under a 10 x loop.
The trouble is finding the brass thickness to do both sides.
What I do is polish the internal neck with an old bore brush wrapped in steel wool placed in an electric screw driver on high speed now and then . It is not the precision of reaming but it does smooth it up quite well after a while .
 
#10
Re: single digit Standard Deviation, what the secret?

Take a look at the paperwork for your chrono and see what is the acceptable percentage of error for your unit. Then figure what the translates to at 2800 fps or so. Now, how much does that single digit SD mean to you?
 
#11
Re: single digit Standard Deviation, what the secret?

I think low ES and SD comes down to each rifle and finding the right combination of powder that will give it to you. I played with 5 different powders in my 260 Rem with the 140 VLD. Only 1 gave me really low ES. The rest were in the high teens and low 20's. The 20 fps ES is a very common spread. It's not that bad, either. At 1K, your talking about 6 inches of vertical with a 308 Win shooting a 175 SMK.
If you are trying to achieve the lowest ES, then experiment with various powders and combinations and see what you get.
 
#12
Re: single digit Standard Deviation, what the secret?

I have found the most meaningful measure of S.D. to be the verticle spread of impacts at 600 yards.

I don't have a chrono, so I shoot at a few distances and back calculate my Velocity at the muzzle.

When doing this I "neglect" wind, hold the same spot and measure the verticle spread. I do make note of the wind speed and direction and compare notes to the horizontal spread.

Really helps me learn to trust my log-book tables.

Hope that helps. As stated above, the tolerance of the chrono may not be as tight as you need to get desired results.

Also of interest, the verticle spread at 600 for my load using winchester brass is more than double the spread using Lake City; but the winchester is still sub-moa verticle.
 
#13
Re: single digit Standard Deviation, what the secret?

DMCI is a mathmatical genious and back when he was hanging around we ran the SD on my loads, at the time I want to say it was 8 -

Black Hills brass, or WInchester, varget, and FED 210M
I chamfered the brass, deburred it, cleaned the primer pocket and weighed every 5th rd.


I used an RCBS powder throw but I think the real key with all of it is keeping that powder throw at the 3/4 level....

My vertical was 3.5" at 600 .


But this load is one that I developed over a season of shooting specific to this rifle, and while it shot NICE in my WInchester the Winchester shot the 155's better, faster...
 
#14
Re: single digit Standard Deviation, what the secret?

Damn interesting and insighfull comments, thanks to each of you.

Chrono mfg says accuract is + or - 1% of measured velo. Thats 56 fps spread! damn, i never thought of that...
 
#15
Re: single digit Standard Deviation, what the secret?

I've noticed since I started shooting 6 Dasher and the 6 RAT that the short fat cases are pretty easy to get some crazy low SD's. 3 dups and 2 other shots within 5 fps for the last 2 loads. They also shoot well at distance.
A powder that pretty well fills the case at the velocity your looking for seems to help. Primers can make a significant difference.
I'm a lot more concerned about downrange performance than bragging rights on low SD's.
 
#16
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Country</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hummer</div><div class="ubbcode-body">When Marine Corps Rifle Team loaded their own 7.62 they had a requirement of no more than 10 SD on their long range ammo. I know they internally neck reamed cases as I used to pick up their brass. </div></div>
Look it makes sense to internal neck ream. We turn the outside of the neck to fit the chamber and give even neck thickness to assist precisce bullet pull etc. However the inside of the neck might look like a moon surface under a 10 x loop.
The trouble is finding the brass thickness to do both sides.
What I do is polish the internal neck with an old bore brush wrapped in steel wool placed in an electric screw driver on high speed now and then . It is not the precision of reaming but it does smooth it up quite well after a while .
</div></div>

+1 on the drill and steel wool. I do this anyway on all my loaded brass.
 
#17
Re: single digit Standard Deviation, what the secret?

I would get a pound of reloader 15 and load develop and see what your numbers drop too. I had better numbers with Reloader 15 than Varget in my 308. Changing/checking different primer combinations also helped lower ES and SD.
 
#18
Re: single digit Standard Deviation, what the secret?

The case neck prep I believe has given me a big return in lowering ES & Sd. Annealing after 5 firings ( neck tension), steel wool clean ID of neck. I once measured run out of bullets seated with out cleaning vs a clean neck about .004 run out on dirty ones. Cleaning the necks is more about neck tension for me.
As others have said powder, primers all play a part.

RL 15 46.1 OCW derived,155L, Lapua Case, Russian LMR primer, Mag Length 2.8 .010 jump, Mod. Palm Chamber, 11.25 Poly Schneider barrel 2940 FPS single digit SD ES 8.4 Mils 1000 yds
 
#19
Re: single digit Standard Deviation, what the secret?

+/-1% pretty much negates the entire point of trying to acheive precise values for ES/SD. The numbers have a low degree of confidence. As absolutes, I doubt them; as values for comparison, I give them somewhat more credence. But still, I'm not betting te farm on them.

My primary interest in chrono values is as velocity figures for calculating drops; and even then, I only consider them 'ballpark' values.

The numerics of ballistics are reliable within limits, but the world holds too many complexities to take such calculations directly to the bank.

In the end, we are left with some generalities (like 1Kyd drop being somewhere between 25MOA and 35MOA) which allow us to find a zero, and then we take the POI's as our key element for measurements and judgements.

The instruments and calculators use batteries, but the target never lies.

Greg
 
#21
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: distantfoe</div><div class="ubbcode-body">I've always had good luck with trying to keep the case as full as possible without crunching powder. </div></div>

Yeah. Some use drop tubes while the only thing I do once my loading block is full of brass and powder is give it a few taps on the side of the loading block settling the powder down in the brass. Works everytime and I hardly ever hear crunching.
 
#22
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: user#1</div><div class="ubbcode-body">Just like so many, I'm measuring each load on an acculab vic 123. Same lot of win 308 brass, varget, cci br primers, micrometer seater, flash holes uniform, and neck tension,,,....only getting SD's in the twenty's is this common with you guys and gals?

Thanks, </div></div>

Once again, my take on SDs:

20-30: most factory ammo

15-19: as a reloader, tighter than most factory ammo

10-14: as a reloader, doing pretty well, things are clicking

9 or below: things are pretty much as good as they're going to get

Chris
 
#24
Re: single digit Standard Deviation, what the secret?

I've gotten some really low ES and SD numbers before, and i'll duplicate the load the best I can, go out, and all the numbers are different the next time out. My former pet load (had to change, it became too hot) gave me a target at a match with 2.5" of vertical dispersion, however when i would run it over the chrono, my Sd would be in the high teens to low 20's. I unfortunately own a rather inexpensive chrono. I don't have the means to buy a high dollar unit that is more likely to give me accurate readings. Wish I knew somebody local with a CED or Oehler.

Branden
 
#26
Re: single digit Standard Deviation, what the secret?

Just went through Load development and used Black Hills as my baseline.

Using a Chargemaster (loaded light) and a DI MXX-123 that was accurate to .02 grain and Sako308 35P (Lord I want one).

All were shot at 300 yards. 100 Yards you can hide too much.

a47bbp.jpg

wr1d2p.jpg

2dkzafb.jpg

wtsl7p.jpg

2iu5c2h.jpg


The term "Match Ammo" is a discussion in itself....
 
#27
Re: single digit Standard Deviation, what the secr

I assume this was your .260, that 42.8 load looks very promising with almost nil vertical dispersion. I'm impressed with that load at that velocity. Were these 139 Scenars?

I wonder why everyone recommends getting the velocity at 2800 or more? Seems like gains would be negligible and barrel life would be a concern. No?

edit: I just noticed the low load at 41.8 looks good too with maybe one low "flyer"?
 
#29
Re: single digit Standard Deviation, what the secr

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Swan</div><div class="ubbcode-body">I assume this was your .260, that 42.8 load looks very promising with almost nil vertical dispersion. I'm impressed with that load at that velocity. Were these 139 Scenars?

I wonder why everyone recommends getting the velocity at 2800 or more? Seems like gains would be negligible and barrel life would be a concern. No?

edit: I just noticed the low load at 41.8 looks good too with maybe one low "flyer"? </div></div>

That low node was intresting. When you run the math on the 42.8 with single digit SD

mip8vo.jpg


Even more troubling is you see how much of the "Nut Behind the Bolt" is the issue. Sub .5 MOA (right to left) and sub .2 MOA (vertical)
 
#30
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: smokshwn</div><div class="ubbcode-body">Also consider that just the conditions for your chrono to function can cause a large degree of variability (light, shadow, angle, etc.) </div></div>

Agree although the 35p is the gold standard though. All the shots were done during the same day and at the same conditions.
 
#31
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chiller</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: smokshwn</div><div class="ubbcode-body">Also consider that just the conditions for your chrono to function can cause a large degree of variability (light, shadow, angle, etc.) </div></div>

Agree although the 35p is the gold standard though. All the shots were done during the same day and at the same conditions. </div></div>

FWIW as a discussion that seems to pop up a lot not only here but in USPSA as we are always being chrono tested at matches. It is not necessarily a matter of the instrumentation being a problem. I would guess that even some budget chronographs can be pretty accurate. However, it is the hundred other factors that we try to control for, but in reality can't.

So my point is that if I have a consistenly good load that produces SD's from 20-25 every time I test it. How much of my effort in trying to reduce it is simply chasing "tolerance stack" of the many conditions that are difficult to control for vs. actual improvement in the load.

 
#32
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: smokshwn</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chiller</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: smokshwn</div><div class="ubbcode-body">Also consider that just the conditions for your chrono to function can cause a large degree of variability (light, shadow, angle, etc.) </div></div>

Agree although the 35p is the gold standard though. All the shots were done during the same day and at the same conditions. </div></div>

FWIW as a discussion that seems to pop up a lot not only here but in USPSA as we are always being chrono tested at matches. It is not necessarily a matter of the instrumentation being a problem. I would guess that even some budget chronographs can be pretty accurate. However, it is the hundred other factors that we try to control for, but in reality can't.

So my point is that if I have a consistenly good load that produces SD's from 20-25 every time I test it. How much of my effort in trying to reduce it is simply chasing "tolerance stack" of the many conditions that are difficult to control for vs. actual improvement in the load.

</div></div>

I do understand "tolerance stack" (BSME, P.E., Minor in Math) that being said....

Here is Black Hills Gold Medal Match ammo.... to compare.

fodvt1.jpg


1.073 MOA Vertical
0.369 MOA Horizontal
19 sd (as opposed to 9 for the "tuned" load)

I do understand I do not want to extrapolate a 4th degree polynomial from a single point....BUT.....
 
#35
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: user#1</div><div class="ubbcode-body">Hey Chller, your a mod now, congrats....cool. </div></div>

All the help this site and its members have done for me. It is the least I can do to help. Besides with CKA....
laugh.gif
 
#36
Re: single digit Standard Deviation, what the secret?

Single digits are nice, single digits and accuracy are great, in all the loads I've developed over the years and chronied my best and most reliable loads are in the low teens. I've never had a single digit load that was the best. I think the chrony has more to do single digits than anything....the group tells me what is the best and the chrony tells me how well they might hold up at distance. We ran test with the 243 using a lee neck sizer, and a redding bushing neck sizer and 2 different tensions a couple of weeks ago to see how it would change things. The Lee was horrible in accuracy and SD. SD on 270 bushing was 7.2 and pretty good accuracy, but the 268 bushing had an SD of 11 and was the best groups the rifle shot all day. They were chronied on the Millennium we have and the test was done because I was trying to get my brother to park the lee collet die. He is now a believer and has done so. If all I did was hunt the Lee would be a great set up because they will get the job done but I do a lot more shooting sitting at the bench than I do in the woods and I want all my bullets touching on paper. I've tried my best and now it's starting to sink in to little brother cheaper is <span style="font-weight: bold">almost</span> always not better. I was proud of him when he bought the Millennium after destroying my Chrony with his 7MM RUM and also proud of Midway for replacing my 8 month old Chrony at no charge. We have also fired loads across both when we set up at the range and I have seen very little difference in the speeds they register so I'm not so hung up on the Millennium as being that much more accurate but I do like the bells and whistles much better and it is well worth the extra coin.
 
#37
Re: single digit Standard Deviation, what the secret?

The secret? Lots of pressure. Want more consistent and complete combustion? Raise the pressure. Race car guys figured it out a long time ago. Higher compression = more power, due to more efficient burn. Rifles are very similar.
 
#38
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">The secret? Lots of pressure. Want more consistent and complete combustion? Raise the pressure. Race car guys figured it out a long time ago. Higher compression = more power, due to more efficient burn. Rifles are very similar. </div></div>

At what point do you get diminishing returns though? There has to be a point in which the powder is getting to compressed and breaking kernels, or some other factor.

Branden
 
#39
Re: single digit Standard Deviation, what the secret?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dust_Remover</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">The secret? Lots of pressure. Want more consistent and complete combustion? Raise the pressure. Race car guys figured it out a long time ago. Higher compression = more power, due to more efficient burn. Rifles are very similar. </div></div>

At what point do you get diminishing returns though? There has to be a point in which the powder is getting to compressed and breaking kernels, or some other factor.

Branden </div></div>

I don't see how that'd make any difference. People have tumbled loaded rounds for days and then shot them and seen the same velocity with the same load.

If you can't get single digit or low teen SDs, use a faster powder.
 
#40
Re: single digit Standard Deviation, what the secret?

always thorght Light neck tension with single fed rounds would yield best acuracy for long range shooting, My Lapua 105g Molly scenar with Lapua brass measures 2.72 and i use a 2.70 bushing for my 243, I might try a 2.68-2.69 as i am using molly bullets which some shooters mentioned might need more neck tension over naked bullets, anyone find more neck tension needed with molly bullets for their 243 win to reduce Es and sd?
 
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