bullet and case weight

Discussion in 'Big Stuff--7mm, 30 Cal, .338+' started by kotkot, Jan 12, 2019.

  1. kotkot

    kotkot

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    HI All,

    question from new member here and my apologies is this has been answered else where. please point me to the answer.

    I think I understand importance of weighting the bullets. (I was shocked to find, that my Hornady 168match bullets have up to 1gn variation, while my SMK 175 are within .2gn of each other)

    but why should you weight and sort the cases? what does it matter if one case weights bit more? Will that have measurable effect on velocity?

    I weight cases after they were cleaned, sized and prepped.

    thanks!
     
  2. misfire

    misfire

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    Variance in case weight can help you determine variations in case capacity the volume of the cases being different will definitely affect velocity between cases.
     
    Last edited: Jan 12, 2019
  3. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    When sorting cases by weight, the general assumption is that the because the outside dimensions should be pretty close (i.e. having all been fired in the same chamber and therefore conforming to its dimensions), that weight should be proportional to internal volume. However, this is not always the case. Variance in the extractor groove dimensions and the location of the shoulder or wall can alter internal volume without affecting weight. I have sorted thousands of cases by weight and internal water volume and I can tell you that you will always find some outliers where case weight does not appear to correlate well with internal volume. Nonetheless, I do sort cases by weight because its much easier and faster than determining water volume. My general feeling is that even with a few outliers, cases sorted by weight will have more uniform internal volume on average than cases that have not been sorted at all. In the grand scheme of reloading, sorting cases by weight is relatively fast and easy if you have a decent electronic balance.
     
    Last edited: Jan 12, 2019
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  4. kotkot

    kotkot

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    Thank you! so assuming you group your brass and bullets by weight..(heavy case with light bullet? ) how much can it affect your POI at let's say 100 yards? what's the best way to compensate for it? or you just accept that your POI will float from day to day and just focus on how tight the group is?
     
  5. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    Sorting case by weight is not liable to affect your results much at 100 yd. That is, unless you're a top level BR shooter capable of groups in the 0.1s (or less), in which case you really should be sorting cases by actual water volume, among other things. However, 600 to 1000 yd vertical in F-Class may be a different story. Many sorting approaches are difficult to define in terms of tangible (readily quantifiable) results. We do certain things because we believe they may make a small difference over time.

    As far as bullets go, I don't try to match up weight-sorted bullets to specific cases, although you could if you wanted. I really am looking only to cull any bullets that are gross outliers in terms of weight.
     
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  6. kotkot

    kotkot

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    Thank you! My goal is to get in to 2in circle at 300 yards consistently. and understand why my POI can shift day to day...not much, but it can be inch off at 100yards
     
  7. Texas10

    Texas10 Gold $$ Contributor

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    First of all, welcome to the land of the accurate shooter!

    Your goal, as I understand it, is to be able to shoot a .66 moa group consistently at 300 yds. Your question(s) are what works and what doesn't to full-fill that goal. But the answer to that is that there is no simple answer. You'll need to shoot, quantify your results, modify, and repeat hundreds and even thousands of times.

    Regarding your question about case volume vs weight, a simple test will provide some answers. Sort out your case outliers by weight and mark to identify. Load those as you do your selected cases. At the range, shoot some 5 or 10 shot groups with the selected cases, then shoot some groups with the outliers. Measure your groups for overall groups size and distance/angle from POA. Account for wind drift. Then back at home, measure case volume of all your spent brass just as it came out of the chamber and before any cleaning or die work. Note any trends and keep thorough records.

    If you do this while using a chronograph, be certain it's accurate and record results.

    In my limited experience, I've only been half seriously into this sport for about 5 years, the ability to shoot small groups come at a certain price.

    To shoot MOA groups one only needs to purchase a good quality off the shelf weapon, ammo and scope and spend some time at the range.

    To shoot sub 3/4 moa groups one needs do the above plus improve your marksmanship skills, go through the weapon system and correct any minor faults in the manufacture, assembly and set up of the system.

    To shoot sub 1/2 moa groups one needs to do the above plus learn to hand load accurately, no small feat, and learn to read the wind accurately, an even bigger feat as well as purchase superior aftermarket parts such as competition grade barrels, stocks, scopes, mounts etc.

    To shoot sub 1/4 moa groups you'll need start with a whole new and top quality custom built and expertly tuned weapon system, hand loading system, and improve your shooting and wind reading skills to expert levels. Join a club that hosts competitions in the area of your interest, seek out a mentor or two, and be prepared to spend many thousands of $$. It helps to have the eyesight and necessary skills too, both mental and physical. If you're a journeyman machinist, you already have a leg up on the quality parts.

    I'm currently in the 1/2 moa group. Being retired and lacking a fat pension or rich Uncle, my budget is fixed. I will never own a custom built system, but I can still have fun with my cobbled together "Franken-Gun system shooting occasional groups in the two's, one's or even zero's when all the planets align. :cool:
     
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  8. seymour fish

    seymour fish

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    That POI shift needs to be sorted out.
     
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  9. Bart B.

    Bart B.

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    If you want to learn how to keep all shots inside 2" at 300 yards, you'll do it the fastest with a top quality rifle, reloading stuff and a top ranked shooter to help you do best with all that stuff.
    With lesser quality stuff, it's going to be harder and take longer to learn what's not performing at its best. It's usually less costly doing this than starting out with lesser stuff.

    Why? Do you want each bullet shot to strike where it was aimed? Or some place else?
     
  10. kotkot

    kotkot

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    Thanks all for the answers! The quest continues...
     
  11. watercam

    watercam Gold $$ Contributor

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    One less onerous way to sort is by weighing loaded ammunition. Claude Audette offered this up some decades ago. You are essentially combining the weighing process. Heavy cases that happen to have heavy bullets are one end of the scale, lighter cases that happen to have lighter bullets are the other. Combinations of the two are in the middle. What you end up with is a box where the heavies graduate down to the lighter rounds (or vice-versa) and have more consistent elevations over 5-20 round strings of fire. I sort by .1gr. increments and load them into my ammo boxes in order. Saves one from weighing twice, once for cases and once for bullets. This assumes careful powder weighing of course which should go without saying.
     
  12. M14AMU

    M14AMU

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    Dude...I made match grade 30 caliber bullets for years and just because I wanted to find out.....I shot ten round groups with a .308 match rifle from 300 yards with as much as 5.0 grains variation in weight and all variation of lots would shoot into a knot-hole at 300 yards!
     
  13. ronemus

    ronemus Silver $$ Contributor

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    I did an experiment several years ago to determine just how much effect brass weight has on .223 loads. I used WW brass (sized, trimmed and deburred, primer pockets uniformed, flash holes deburred, and neck turned), WSR primers, charges of RL-15 or N-550 powder weighed to 0.1 gr, and 75 gr A-Max bullets. Using the lightest and heaviest cases (sorted from 1000 once-fired I had on hand), I had two lots of 10 cases with a 3 gr difference in weight. The average muzzle velocity difference was 16 fps, just a bit more than the 12 fps due to 0.1 gr of powder. I choose to sort 0.5 gr lots of .223 brass for my long range loads, but the effect will only matter at 800-1000 yards - the vertical displacement on the target from such a small velocity change is negligible at shorter distances. Unless you control all other sources of variation, the effect of brass weight is negligible. I also shoot .284, and because the brass is twice as heavy I batch in 1 gr lots.
     

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