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difference in case weight impacting accuracy for .308?

Discussion in 'Ammunition & Reloading' started by mr comer, Jun 10, 2013.

  1. mr comer

    mr comer Salem New Member

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    I noticed my Hornady match varied up to 6.5g, Winchester varied 3.2g, and federal varied 2g. Weight was taken after tumbling and cases were still capped. I've only shot the Hornady all the rest are one-shots sitting on the shelf. I wont mix the brands of cases but should I separate cases by weight? How much weight difference should there be? I'm thinking about switching over to the Winchester with it's lower variance. Or am I just being OCD :)

    Thanks in advance for any advice for this newbie re-loader.
     
  2. DieselScout

    DieselScout S Clackamas County Well-Known Member

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    I think you're being OCD, but there are people who may shoot well enough for it to make a difference to them. Since you're a "newbie re-loader" I am going to guess it's not going to make any difference to you either. What bullets are you shooting? Are they sorted for weight? Have you measured your jump or lead? How is it effecting your accuracy? Are you uniforming case mouths, neck sizing, full length sizing, has your action been blue printed....etc? I am not trying to be a jerk, just giving examples of what some people do for accuracy and how many minor details can affect it.

    Regardless, the question was will it affect accuracy. My answer is simple, do you shoot well enough to notice? I frankly would be more worried about bullet weight consistency and jump then case weight.
     
  3. bellarum

    bellarum beaverton Well-Known Member

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    Read a couple of reloading manuals cover to cover a couple times first. I full length size, trim to length, chamfer, debur, uniform the flash hole, clean the primer pocket and start working up a load while running it over a chronograph and checking for signs of over pressure. If you want to get real crazy you can measure the case volume,weigh projectiles, primers. I wouldn't bother weighing cases until they are completely processed.
     
  4. Mark W.

    Mark W. Silverton, OR Bronze Supporter Bronze Supporter

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    Its not the weight of the case that effects accuracy its the volume of the case. Since a sized case has the same external dimensions as the next. Weight can be used to determine which case has a larger volume. IE. the lighter weight case has more powder volume. The more volume a case has the longer it takes for the pressure to come up to a point that the slug starts to move.

    So yes variations in case weight does directly effect accuracy. Now if your trying to hit beer cans at 50 yards with your AR-15 being that picky is a joke. If on the other hand you are trying to shoot a 5" group at 1000 yards with a .308 then the difference is worth the effort.

    Long rang shooters go to great pains to insure their cases are as closely matched as possible.
     
  5. Shooter98

    Shooter98 McMinnville, Or. Member

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    I don't think you're being OCD at all. If you're purchasing Hornady MATCH brass, then that's what being MATCH is all about. The brass should all weigh nearly the same in each batch. Meaning if I buy a bag, I expect each piece to weigh nearly identical. The weight difference is due to the thickness of the brass, meaning a heavy piece probably will have slightly higher pressure when fired compared to a lighter piece of brass with the same charge. This ABSOLUTELY will change the point of impact! When I load, I separate my brass out to withing .5 gr of each other. By doing this, when I am shooting the rounds and I go from one weight of loaded round to the next weight, then I won't be so critical of accuracy, but if I am shooting ammo that's all the same weight then I expect better accuracy. Trust me, it makes a huge difference, unless all you care about is hunting, and you're just worried about one good shot. I reload for ELR shooting and I base all my accuracy from 600 yards and beyond.
     
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  6. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    The real answer to the question is "Depends on the capabilities of the rifle and shooter".

    In many, if not most instances weighing cases along with most of the other case uniforming processes is along the same lines as buying "Super High Performance Z Rated Tires" for your plain old off the showroom Ford Focus.

    If your rifle and skills can't make use of all this "Uniforming", then all it does is give you something to do with your time.
     
  7. Shooter98

    Shooter98 McMinnville, Or. Member

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    Not that I totally disagree with this statement, I always felt it was an ambiguous statement. Some people never learn the true potential of their rifle or their skills because people tell them that they're being too finicky about little things. It's my opinion that when you start chiseling away at the little things and remove them from the equation that the true potential starts to show.
     
  8. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    But let's face it, no amount of "nit picking case prep" or micro-minutiae management with reloading will change that "Monthy Special" rifle that off the rack at Cabela's into a Bench Rest quality firearm. There does come that point of diminishing return.

    Now if you have a custom that has a chamber optimized for a particular bullet, and every part of that rifle is built for consistency, by all means, finish the job with nice uniform ammo.
     
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  9. Shooter98

    Shooter98 McMinnville, Or. Member

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    Like I said, I don't totally disagree with your statements. You make good points.
     
  10. Otter

    Otter Oregon - mid Willamette Valley Active Member

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    I shoot 6PPC, 6BR and .223 for accuracy. I don't bother weighing brass or measuring internal volume, although I did try it at one point with no measurable difference. (I shoot 300 yards and less...600-1000 yards I might try it again out of curiosity.)

    If you don't shoot with wind flags, you are not going to realize the benefits of any of these tuning tricks. Start using some sort of wind indicator, even if it is only ribbons on a dowel, and your groups will tighten up far more than by doing anything else.

    If you want consistent high quality brass, buy Lapua. Winchester is a second choice. I won't buy anything other than those two because of inconsistency, including weight, internal volume, neck wall thickness and banana shaped cases.

    Amendment in light of Southpaw's post: I agree Norma makes very good brass. A little softer than Lapua but excellent brass. Nosler brass is suppose to be weight sorted brass made by Norma, so I would add that to my buy list if it was available. If I have a choice though, Lapua is my first choice.
     
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  11. SinisterSouthpaw

    SinisterSouthpaw SW WA Active Member

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    ............that point being that I would throw the Winchester brass out of the premium quality brass category and add Norma. I can't agree more that one of the major failings of beginners who want to shoot for ultimate or just decent accuracy, if not THE major failing, is the lack of understanding when it comes to the use of wind flags. Without using and learning what they mean to your downrange performance you will never be sure what caused your load to be doing what it does/did downrange...especially over 100 yards. And really, who shoots and does not care where the bullet went? or will go? Who does not want to get the best out of whatever firearm they use? Maybe gangbangers who shoot pistols sideways have different priorities, like looking cool while missing the target, but I think the rest of us could get some help from the flags.................


    That being said, I do think that weighing standard grade brass can be worthwhile as long as you do it in a way that tells you something useful. I think wieghing a box of 50 cases is a waste of time, except if you find that some cases weigh over or under the midrange, or median, weight by 5% or more. I say midrange--not average--

    What is the difference between Mean and Average?


    BTW--5% is a pretty big difference but I have seen it in standard grade 5.56 (.223)brass, and once in some .30-06.

    A better indicator of usefulness/weight is to do this in batches of 200 or more cases--throwing out--or if you are a miser like me--saving the culls in case future lots are more like them. The advantage of using a larger sample of cases is that you may find a useful number of them outside the midrange and be able to form 2 or 3 boxes of 50 that do not vary in weight by more than 3% or less if you have higher tolerances in mind. If you do this a few times you begin to see the advantages of buying the better grade brass..........
     
  12. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    A good alternative to weighing brass is to focus more on what really matters, volume.

    Of course there is the water capacity method where a dry case is weighed and then filled with water, the difference in weights being the "capacity" in water.

    Another, simpler method is to take a very fine ball powder and fill your fireformed cases before they're de-primed. The fine ball powder will settle quickly and have minimal air space. When filled with powder, strike off, and then pour the powder into the scale pan and weigh. Record the weight, mark the case, and then just pour the scale pan's contents into the next case. Add or strike off if necessary.

    Pretty soon you'll have a quantity of cases with the volume of powder marked on them and you can assemble them into groups of equal volume. This eliminates all the variables like extractor groove depth/width or rim thicknesses, that will show up as weight differences but not affect the internal volume.

    I've tried this a couple of times recently just to prove the concept using CFE223. Others have recommended some of Hodgdon's fine ball powders for the task.
     
  13. mr comer

    mr comer Salem New Member

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    Thanks for all the replies. I decided to sort out my 200 plus cases of Hornady match cases after de-caping and resizing. There was over a 6 grain difference. I'm an experienced and successful competitive shooter (archery) and a would like to be as accurate as possible but I have a very limited budget. I'm shooting a 700 sps tac, timney 510, bell and carlson light tactical stock, harris bipod, vortex scope. I'm using varget, smk's, cci 200 primers, and loading as accurately as possible. I shoot up to 600 yards regularly and am trying out to 1k. A majority of the cases are within 2 grains of each other. Should this be close enough? I would like to have lupa or norma brass but again the budget is tight.
     
  14. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    If "Weight Matching" is important for you, here's one way to get uniform groupings. Weigh every case and line them up on a long piece of paper showing .2gr segments. When done, you're finished you'll have groups that are larger than others. Then fill a cartridge box using cases from these "groups". If you are a few cases short to fill the box from a single group, then use a case or two from the group just heavier or lighter. After you have the majority boxed in "sets", then just box the remaing cases from the scattered groups and use them for sighter/foulers.

    I've known some shooters that will buy large quantities of brass and sort into only one or two boxes of 50 for their competition. The rest they sell on the Club Bulletin Board or Online.

    Funny thing is that some of the shooters that spend the most time like this aren't the ones winning all the time. If you don't have a rifle and the skills to take advantage of carefully matched ammo ------------
     
  15. evltwn

    evltwn Gold Hill Oregon Bronze Supporter Bronze Supporter

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    Deadshot is correct, of course. And this thread is covering only one of many variables to be considered when attempting to build consistent ammunition. Powders, primers, projectiles, fireforming, neck truing, flasholes, primer pockets...just to name a few. I should also endeavor to somehow become a half century younger, get lasik surgery and eliminate the shake from my right hand, all of which would improve my scores.
     
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  16. BoonDocks36

    BoonDocks36 Oregon, in the boondocks Christian. Conservative. Male.

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    Great thread !!!

    For "minute of pie plate", just follow good reloading practices. I started reloading, with the Original Lee kit, in 357, you know, the hammer primer out, resize, and a little yellow pwder scoop for a set number of powders & bullet weights.

    Now 35 years later, I am amazed in what I did back then! i am just setting up, my Third reloading bench, from moving from place to place, i am still reloading 357, but with much better equipment, and with many more bullet weights.

    Now to the point: I bought a 1500 cartridge box, of 7.62X51 all advertised "fired from machine guns".

    Oops! As I started sizing them, it became obvious, I bit off a bit more than I desired to preform, at that time anyway !!! I had just read an article on variable Volume in same cartridges, and since I was laid up from difficult work... I took to weighing those cases!

    I came up with five MAJOR groups of cases, with a few oddballs thrown in.

    My thinking at he time: Load groups A, B, C, D, E as seperate parcels of loading variables, and then log them in my reloading log book.

    RELOADING LOG book, is an important item if your really interested in Better than Minute of Pie Plate !

    Other things I did after that thinking exercise:

    A. Use color codes for A,B,C,D,E use marks all pens.
    B. keep all other variables Out of the equation !!!
    C. strive to shoot portions of all batches, on the same day, that kept windage variables to a minimum.

    Those things are just good practice.

    Keep all your reloaded ammo seperate by batches: ie. you have reloaded batch A 5 times, & reloaded batch B 10 times, they are not equal in quality, unless you have been loading very low power rounds, even then, twice as many shootings is more wear on the brass.

    HTHelps,

    philip,
    Who says "we were all newbies once, no matter how long ago"

    And with SomeTimers Syndrone, even Newbies Twice !!!
     
  17. Darkker

    Darkker Mesa, Wa Active Member

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    The WEIGHT of the brass is at best, a poor indicator of capacity. Powder cares about volume, not weight.
    If you want to be consistent, STOP weighing your powder! Dispense it by volume. MOST powders have a nominal lot variation of 5-10% in burning rate anyway. The only way to control those differences(speaking specifically to extruded powders) is by volume. THAT method accounts for the VERY tight BD/BR ratio that is held in manufacturing. Weight of powder doesn't account for that.

    If you want to sort your brass, sort by capacity, not density of metal.
     
  18. Otter

    Otter Oregon - mid Willamette Valley Active Member

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    Darkker, do you have any on-target proof of this theory? I've heard this before and have no proof to argue with you. People that shoot short range BR do indeed throw charges by volume, but they always talk about if their throw is accurate in + or - grains, not volume. And lots of short range shooters are now going to weighing charges with the RCBS setup rather than using their powder throws. Certainly the long range people are fanatical about weighing charges, some of them using laboratory quality scales.

    I fully agree with you about case volume compared to weight. Weight means very little with regards to actual case volume.
     
  19. BoonDocks36

    BoonDocks36 Oregon, in the boondocks Christian. Conservative. Male.

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    Darkker, I am just slightly puzzled on your post.

    Given: an outside shape, which does not vary, and the cartridge ~varies~ in weight, one can see that Internal Volume of the case will be different. i can see no other conclusion, and I have decades of Metal Casting work, in Bronze, Silver, Gold and White Gold (alloyed with Platinum, just to be specific).

    Mass and Volume are not equivlant terms.

    Mass versus Volume, both defined at Dictionary.com - Free Online English Dictionary

    Mass, df.
    "In everyday usage, mass is often used interchangeably with weight, and the units of weight are often taken to be kilograms (for instance, a person may state that his weight is 75 kg). In proper scientific use, however, the two terms refer to different, yet related, properties of matter."

    Volume, df.
    "1. (Mathematics & Measurements / Units) the magnitude of the three-dimensional space enclosed within or occupied by an object, geometric solid, etc. Symbol V"

    An ounce of silver, can be contained within X volume, or Y volume, depending on its molecular density, same with brass, bronze, feathers.

    If you Coin silver, its density is compressed until it can no longer be any smaller in volume, however, if you anneal silver, it "relaxes" the molecular structure, there for, it is (minutely) larger in volume than Coined. This can be measured!!!

    In our topic, the exterior of the cartridge is ~set~ dimensions.

    All cartridges Weighing the same, will there by Have to have, the same Volume.

    The issue of Volume versus weight,of gunpowder can be shown in my above examples of ~coin~ silver: If you take a set Volume of GP, it is Possible, to compact it, Yes? And even, Further compact it.

    The Density of that compacted GP is analogous to the compacted molecular structure of the Silver.

    HOW that compacted GP reacts to Heat or a Primer pop, is & Will be different, than Loose GP !!!

    The Weight of GP may not vary, but its volume will, and That Volume, contained in a heavier (hence smaller voume/area to fill) Cartridge should act much different, than the same Cartridge which weighs Less, Hence having a Larger Volume to fill.

    I am Not talking a miniscule difference of volume, but in my 7.62X51 Nato, the extreme difference was some 15-18 grains, a lot of metal... Accuracy would Have to be improved, by tightening the extreme difference to a couple grains Max.

    My Cartridges were used in a Machine Gun, nothingthere is real accurate shooting, its Spray it out...

    Not what a precision shooter would be doing, and they would probably by Better Brass to start out with.

    When I approached the issue at hand, it became "classify" the weight groups, keeping them Close in their weights, all the cartridges were ~good to use~ But Not all would shoot to POA, with the same powder load.

    Please correct my thinking if I have made errors in above, I am not trying to argue, just clarify issues of Cartridge Volume & Powder Density within same.

    yours,
    philip ...

    (And if I did not make it plainly understood, above, the entire issue was never resolved, due to medical issues, I could not Work the brass when I bought it, only discovered the difficulties via resizing issues: smaller volume cases, more metal, harder to resize.... i still have the last cartridge Stuck in that die!)

    Please accept mis spellings, etc. due to iPad keyboard issues!
     
  20. deadshot2

    deadshot2 NW Quadrant WA State Well-Known Member

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    BoonDocks36-

    Much of what you say is true but when it comes to brass cartridges there are some differences. First of all, NATO cartridges are a terrible example because they do vary so much from mfr to mfr and even within the same mfr's product. Take a look inside a few NATO cases that have been cleaned with SS media so you can see the profile inside the case head. Yes, the external dimensions are the same but the mandrel used to form the case can have several different shapes. Some leave the inside of the case head flat, some stepped, and some concave.

    When you get to "civilian brass" the weight variations can be much closer than with NATO. Close enough that a variation in extractor rim thickness or groove depth (all within "spec") can be the reason for the weight variation.

    If one wants to make sure that the cases are truly matched, go ahead and weigh if you wish. But then check the volume using either the water fill method or a fine grained powder that will settle in the case without a lot of fuss. Fill the case, strike off the powder at the mouth, then pour into a scale pan and weigh. Record and repeat. All theories aside, the way to be absolutely sure of what the case volume is, is to measure the volume.

    BTW, anyone know how much weight that carbon contributes to case weights? Actual measurements of case weight, before and after cleaning with SS media or in an ultrasonic cleaner, one fellow shooter has recorded as much as .2 gr difference.
     
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