case capacity, gr water???

Discussion in 'Reloading' started by upacreek, Dec 29, 2013.

  1. upacreek

    upacreek Well-Known Member

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    So like a nerd I am examining all my reloading manuals and came accross something unusual. The nosler 7 guide calls out gr. water for every load. They use the same case but this measurement varies significantly. At first I assumed it was due to seating depth. But it isn't consistent with this theory. Does anyone have any insight? The nosler book is really nice how it's detailed and calls out specifics. The only thing it leaves out is which bullet the loads are based off of. Bearing surface being what comes to mind regarding this area.
     
  2. Greyfox

    Greyfox Well-Known Member

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    I'm not sure this explanation is right in terms of what you are referring to in the Nosler manual which I haven't seen, but I use water to evaluate the caacity differences between my brass cases, and loads. When I develop a load that I consider to be optimum, I will fill the prepared(trimmed and sized) case with the primer hole plugged, fill it completely with water, and weigh the case. I then subtract the empty case weight to get an exact capacity of the case. Since load performance can vary based on case capacity, this gives me a reference point should I change to a different lot, or brand of brass. It will also give an indication of case capacity differences between new, neck sized, or FL sized cases. This may be the difference the water capacity of the loads shown in the Nosler manual. Due to the component shortage I picked up some Norma 300WM to back up my supply of Winchester brand cases. The difference in case capacity between the two brands was 2.3gr, the Norma having greater capacity. Actual performance was different. The capacity between 260 Norma and Lapua brass was within .5gr, and performance was identical in terms of accuracy and velocity. This was an easy switch except for a having to use a smaller neck bushing with the Norma brass.
     

  3. upacreek

    upacreek Well-Known Member

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    In the manual there is around 3gr difference with the same brass mfgr (it is specified) for the same caliber. The 7wsm has like 5 bullet weights. Each weight has the primer and brass called out. But the water gr. varies in my mind quite a bit. Just thought it was weird. Nosler is more detailed than my other books, but this kind of inconsistency makes me wonder if it's not fluff to look detailed. Maybe someone could shed some more light on the subject.
     
  4. Mikecr

    Mikecr Well-Known Member

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    Probably volume occupied or changed by different seated bullets, to same COAL.
     
  5. upacreek

    upacreek Well-Known Member

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    That was my first thought, but not likely.

    7WSM 120gr.........76.8gr water
    140gr........74.5gr water
    150gr.........73.5gr water
    160gr.........74.3gr water
    175gr.........72.1gr water

    7RM. 120gr.........81.4gr water
    140gr..........77.8gr water
    150gr.........78.0gr water
    160gr.........80.4gr water
    175gr........77.0gr water

    300WM 125gr.........85.8gr water
    150gr.........81.7gr water
    165gr........81.1gr water
    180gr........82.3gr water
    190gr........81.2gr water
    200gr........77.4gr water
    220gr........79.6gr water

    My suspicion is there is no logical answere. Maybe a typo.The 7WSM used Winchester brass, but the others call out nosler brass.
     
  6. Mikecr

    Mikecr Well-Known Member

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    It's a screwy system there and I wouldn't credit it as useful.
     
  7. Gunpoor

    Gunpoor Well-Known Member

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    Quote, "They use the same case but this measurement varies significantly." End quote

    These aren't the same case, they are completely different calibers and therefore will have different case capacity.
     
  8. upacreek

    upacreek Well-Known Member

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    As stated above the 7WSM specifies Winchester brass. The other two specify nosler brass. I would have hoped that since they were giving reloading data that the base cartridge would have been consistent for a given round. Such as all the 7RM data being within a few gr. water for each bullet weight. The spread in capacity concerns me. I don't use these manuals for much more than a refrence anyway. Like the hornady manual is so vague it's not funny. It would be nice to see consistent data though.
    The only reason I asked the question is because sometimes I assume I know the asnswer when the truth is something different entirely. Since no reasonable explaination has been given I assume the info is not as reliable as I would hope it to be and I will proceed accordingly. Just trying to learn.
     
  9. g0rd0

    g0rd0 Well-Known Member

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    according to Homer Prowley here is the method for finding case capacity with water but first you need to know some abreviations.

    ratio of charge to bullet weight (RCBW), sectional density (SD), ballistics co-efficiant (BC), case capacity (CC), expantion ratio this is the ration of expanding gas in your barrel not how much your bullet expands on impact, (ER)
    1. useing brass from the same company, and if possible lot number once fired in YOUR rifle
    2. neck size only, then clean, then trim to length
    3. weigh them empty, (you need 10 pieces of the same length and weight)
    4. now weigh your 10 bullets (be sure they are the same weight)
    5. useing the bullet you intend to use, with a q tip lightly lube the inside of the case mouth and with NO primerand no powder place the bullet in the case and chamber it in your rifle. As the bullet hits the rifleing it will seat it to the required length
    6. weigh these 10 dummy rnds and add the total weight, divide that by 10 and you have your average (if your brass is the same length and weight and your bullets are the same weight then your 10 dummies should all be the same weight)
    7. useing a hypodermic needle fill the dummies with water through the flash hole useing q tips to dry out the primer pockets
    8. now weigh them again add the 10 then divide by 10 to get the average weight, (because of air bubbles there may be a slight differance)
    9. subtract the " average of the "wet" from the average of the "dry" and you have your case capacity of water FOR THIS RIFLE AND BULLET COMBO ONLY


    From this figure of "CC" and from the distance of the base of the bullet from the above "dummy" to the muzzle you can work out "ER", knowing your "BC" and "SD" numbers plus your true barrel length and "CC" together you can now use a slide rule to determine your powder, charge, "RCBW", velosity, chamber preasure and bullet drop.

    SO, when you have at hand reams of confermed PUBLISHED reloading data why would you bother?
     
  10. upacreek

    upacreek Well-Known Member

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    Gordo, please elaborate on what you are trying to say. Don't beat around the bush. Are you trying to imply that I have reams of accurate reloading data in these manuals?
    My question (because I am simple minded) is if anyone knows why the manual has such a large variance in case capacity per given cartridge. Maybe this variance is acceptable and I just am over thinking it.
    If you are implying the manuals happen in real life then you have a different experience than me. I rarely see published results. I can lay 5 manuals of different sources next to eachother and get very different "published" data. When I tryand duplicate these reams of data, there never seems to be validation on my end. And YES I try and eliminate variables such as casem mfgr, primer, ect, ect.
     
  11. Mikecr

    Mikecr Well-Known Member

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    It's Powley.

    But the bottom line is; we don't charge cases with water, we charge them with powder.
    It's that simple.
    I suggest OP skip on by whatever is going on at that section of the manual, and go to the loading section.

    Or, rake that manual into a trash can, and work up a load based on the results of others here:
    The Rifle Section @ www.reloadersnest.com
     
  12. HARPERC

    HARPERC Well-Known Member

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    I liked Greyfox's input I'll have to think on it. I've got an old Powley slide around here somewhere. The only use I get out of case capacity is relative comparisons of cartridges. Especially so when someone is talking a new wildcat, similar capacities similar results.
     
  13. g0rd0

    g0rd0 Well-Known Member

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    my bottom line is trying to explain CC is like trying to explain the holy trinity to a pagan. It is a nice concept if you can understand it but, leave that to the scientists and lab rats at the offices of Lyman, RCBS, Hornady, Speer & etal
    These labs have all the toys to ensure that you can make safe & accurate ammo, so don't get caught up in it.