Help support WeTheArmed.com by visiting our sponsors.

Author Topic: Sample Size for Testing Loads  (Read 7958 times)

only1asterisk

  • Just some guy, you know?
  • Senior Contributor
  • *****
  • Posts: 2405

  • Offline
Re: Sample Size for Testing Loads
« Reply #25 on: January 28, 2013, 09:41:21 pm »
You may have to load more powder behind the 200 than the 220 to reach the same pressure depending on the bullet designs.  Load 10 or so at 13, 12.5, and 12.  Loading subsonics is backwards.  Start with 13 and work down.

WeTheArmed.com

  • Advertisement
  • ***

    THE NORSEMAN

    • To preserve liberty, it is essential that the whole body of the people always possess arms, and be taught alike, especially when young, how to use them. - Richard Henry Lee
    • Moderator
    • Senior Contributor
    • *****
    • Posts: 5071

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #26 on: January 28, 2013, 11:31:28 pm »
    A big part of your extreme spread issue is related to what you're trying to do.  When you go that slow, you're getting very close to sticking a bullet in the barrel.  Especially with those relatively heavy slugs with a long bearing surface. So watch for that very caefully.  Best simple explanation:  Try pulling a tight cleaning patch or bore snake through a barrel very slowly but consistently.  It'll be a bit hitchy.  Do the same thing in a rapid manner, it'll be smooth all the way. 

    That make sense?
    This may be considered as the true palladium of liberty. . . . The right of self defence is the first law of nature: in most governments it has been the study of rulers to confine this right within the narrowest limits possible. Wherever standing armies are kept up, and the right of the people to keep and bear arms is, under any colour or pretext whatsoever, prohibited, liberty, if not already annihilated, is on the brink of destruction- St. George Tucker, Blackstone's Commentaries

    Outbreak

    • NRA Basic Pistol Instructor, Certified Sig P-Series Armorer
    • WTA Staff
    • Senior Contributor
    • *****
    • Posts: 11465
    • Outbreak Monkey ^

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #27 on: January 29, 2013, 12:13:14 am »
    A big part of your extreme spread issue is related to what you're trying to do.  When you go that slow, you're getting very close to sticking a bullet in the barrel.  Especially with those relatively heavy slugs with a long bearing surface. So watch for that very caefully.  Best simple explanation:  Try pulling a tight cleaning patch or bore snake through a barrel very slowly but consistently.  It'll be a bit hitchy.  Do the same thing in a rapid manner, it'll be smooth all the way. 

    That make sense?

    Yup.

    I know I'm pushing them slow, and I was watching for impact on every shot. Never thought about the bore-snake analogy. Makes perfect sense.
    TexasOutbreak

    I take my coffee black...like my rifles.

    I absolutely despise Glocks. That's why I only own two.

    I'm glad that your chains rest lightly upon you. --JesseL

    1911Man

    • Lurker
    • Posts: 3

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #28 on: February 07, 2013, 11:44:12 am »
    Back to the original question, I believe 4 or 5 rounds per load to be perfectly adequate, at least during the "course" work of finding which powder and roughly which amount.

    What I'm looking for is not just the smallest group. I also want to find a powder whose groups, no matter how small, don't jump all over the paper as the amount of powder changes. And I want to find a load which not only has a small std dev of velocity at the accuracy powder amount, but also small std dev at amounts on both sides of it. Many times, I have found "accuracy loads" which are surrounded on both sides by utter garbage. I don't trust those at all. What if the weather changes? etc.

    Five powders times four or five amounts spread by 0.5gr times four or five rounds each - per bullet choice - and the data will really tell you a clear story. That's the "course" work. Then, working with the one or two powders that show promise, four or five amounts spread by 0.2gr times five rounds each - per bullet - and you'll have a really, really good picture. Then, if you're a bit OCD like me, a third pass with one powder in 0.1gr increments times five or ten rounds each, shooting alternately to spread the other variables across the samples, and you are done.

    Assuming you don't want to try different primers or different seating depths, of course.

    Before beginning, I run about a hundred iterations of measuring my throat depth using a once-fired case that has been split down the neck with a Dremel and pinched a tad (so the bullet can move, but there's good friction), using a seating depth mic. There will be many outliers, due to stiction with the lands pulling the bullet out a random titch etc., but 100 or so samples will show you a bell curve with a pronounced spike at the actual COL where the bullet just touches the lands. Then I back off 25thou from there, for all my guns, and eliminate COL as a variable in the accurace load chasing formula. 25thou might not be perfect, but it's important to eliminate variables which matter less than other variables.

    And, on that note, I just use CCI primers. Others might be better, but I don't want to spend time on it.

    btw, if you can afford it, get the German Kurzzeit chronograph. It is at least a million times better than my old Shooting Chrony Beta Master p.o.s. Spendy as hell, though.
    Oregon

    booksmart

    • Token Left Leaning Idealist Libertarian
    • Senior Contributor
    • *****
    • Posts: 6668
    • E. Pluribus Unum.

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #29 on: February 14, 2013, 02:43:37 pm »
    I did find this over on 300BlkTalk.com:

    http://www.300blktalk.com/forum/viewtopic.php?f=128&t=73274

    Quote
    Q: Reloading... What powders are best?
    A: Nearly all supersonic ammo reaches the highest velocity with H-110/W296 powder, or close variants such as 295 or 297. Many people like N110 - and it is fine to use, but it will not attain as high as velocity. For subsonic in the AR, stick to bullets 208 to 240 grains and A1680 will cycle all rifles. 4198 or RE-7 - which do not always fit into the available space, may also be used. 980 fps is probably the best velocity - as bullet flight noise increases a lot as speeds get higher. Note that 300 Whisper(R) loads often recommend N110 or H110 for subsonic. These will not work in 300 AAC BLACKOUT given the way (thankfully) most rifles are designed to be compatible with full power ammo without requiring adjustments.

    mnw42

    • Minister of Silly Walks
    • Senior Contributor
    • *****
    • Posts: 2267
    • NRA Cert. RSO, Pistol & Shotgun Instructor

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #30 on: March 01, 2013, 09:35:35 am »
    I see H-110/W296 and I think .30 Carbine or .357 rifle loads.  When I think of AR loads those are not powders that come to mind.  I haven't looked at loading .300 BLK, but it is good to know that it will use powders that I already have on hand.
    Pennsylvania"A government is a body of people, usually notably ungoverned." -Book -- "All war is deception" -Sun Tzu
    Quis custodiet ipsos custodies -- omnia dicta fortiora si dicta Latina -- History is scary - It keeps on coming true! -- Ni!

    booksmart

    • Token Left Leaning Idealist Libertarian
    • Senior Contributor
    • *****
    • Posts: 6668
    • E. Pluribus Unum.

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #31 on: March 27, 2013, 12:01:14 am »
    Outbreak, any new developments?

    Outbreak

    • NRA Basic Pistol Instructor, Certified Sig P-Series Armorer
    • WTA Staff
    • Senior Contributor
    • *****
    • Posts: 11465
    • Outbreak Monkey ^

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #32 on: March 27, 2013, 06:26:00 am »
    Nope.
    TexasOutbreak

    I take my coffee black...like my rifles.

    I absolutely despise Glocks. That's why I only own two.

    I'm glad that your chains rest lightly upon you. --JesseL

    mattitude

    • annoying a-hole
    • Contributor
    • ****
    • Posts: 1854
    • 100% disabled veteran
      • Ramblings of a Disabled Veteran

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #33 on: April 08, 2013, 11:54:10 am »
    What powder scale are you using...balance beam or electronic?  For electronic I've found the Lyman 1200 DPS is very accurate and consistent, Hornady Lock & Load not so much (which is what I have now and don't use anymore).  I've gone back to my Dillon magnetic dampened balance beam scale as it's much more accurate and my consistency is excellent.  Also when you load do everything in 1 large lot.  If you load a few samples at one time, then take a break or load some more the next day you will more than likely run into problems and can render your data useless or at the very least confuse your results.  Lastly I've been loading 5 round samples mostly because projectiles are hard to come by these days and I just can't afford to shoot up all of my stock for development.  Get a good stable rest and check out a rear monopod as they work pretty damn good.

    I've never loaded subsonic rounds but from what I researched when I had my SSG PIII (I never ended up getting a can for it) excess case volume w/o fillers caused higher extreme spreads.  I believe it was mentioned before, but you might want to start from the higher end and go down to subsonic levels for your higher elevations and your projectiles should have the stability.  You should shoot for around 1050fps.  I *think* I remember reading on silencertalk.com they did velocity testing with & w/o cans and in most cases velocities were increased by around 25-50fps with the suppressor installed...you might want to check that out for yourself.
    North CarolinaMedically retired Air Force (17 years, 7 months & 25 days)

    Outbreak

    • NRA Basic Pistol Instructor, Certified Sig P-Series Armorer
    • WTA Staff
    • Senior Contributor
    • *****
    • Posts: 11465
    • Outbreak Monkey ^

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #34 on: April 09, 2013, 09:31:24 pm »
    I'm using a basic RCBS electronic scale, or sometimes MJElsik's RCBS trickler thingy (automatically trickles powder to the weight you programmed, with built-in scale.) Nothing fancy.

    Before you poo-poo the electronic trickler-scale thingy, we've both had very good results using it. Half-MOA groups, easily.
    TexasOutbreak

    I take my coffee black...like my rifles.

    I absolutely despise Glocks. That's why I only own two.

    I'm glad that your chains rest lightly upon you. --JesseL

    booksmart

    • Token Left Leaning Idealist Libertarian
    • Senior Contributor
    • *****
    • Posts: 6668
    • E. Pluribus Unum.

    • Offline
    Re: Sample Size for Testing Loads
    « Reply #35 on: April 22, 2013, 05:26:58 pm »

    Help support WeTheArmed.com by visiting our sponsors.