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Thread: Bullet seating depth into the case body

  1. #1
    Member RainGull's Avatar
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    Default Bullet seating depth into the case body

    What are the effects when a long bullet is seated further back into a case?

    A lot of short actions do not have sufficient room in the magazine well for long bullets without pushing the bullet back into the case. How far is too far? Does this increase pressure as the bullet is seated further in?

    Thanks.

  2. #2

    Default effects

    The major effects are reduced case volume (loss of powder capacity) . Some of this problem can be reduced by bullet choice; choose bullets which have lead cores they tend to be shorter than monolithic bullets, choose flat base bullets( the BC may suffer), choose bullets with a smaller numbered ogive ( round nosed versus balistic tip).
    " Americans will never need the 2nd Amendment, until the government tries to take it away."

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    Member RainGull's Avatar
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    The spark that led to this question was hearing that the 6.5-284 Norma could not work in a short action with 140 grain+ bullets. But then I am not sure if they start seating on the ogive before they are short enough to cycle.

    I was starting to pine after a 6.5-284, but if I cannot load the longer bullets then I would rather jump ship perhaps to a 6.5 SAUM or 270 WSM. SAUM case being slightly shorter than the WSM or 284.

  4. #4

    Default OK

    You shouldn't have a problem with the 6.5-284, lots of people are building them. I've got a 6-284 that shoots the long 107 grn target bullets at High Velocity and seating isn't a problem, Because I built it on a long action. These bullets are a little shorter than the 6.5 tho. If you will choose a premium bullet flat based 140 grn. bullet it will be doable, I'll BET. But ask Murphy, I'm sure he has a logical answer.
    " Americans will never need the 2nd Amendment, until the government tries to take it away."

    On the road of life..... Pot holes keep things interesting !

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    Member RainGull's Avatar
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    I read somewhere that it didn't work, but then I'm sure you know how that goes. I really like the numbers of 140 grain+ .264 bullets (as well as the 150 gr. .277 bullets numbers) and would not want to lose out on them or have to build on a long action to make it work.

    The SAUM is a bit overbore in 6.5 and the really long .277 bullets would run into the same problem in the 270 WSM I would imagine, (maybe the 270 SAUM too) so my options are limited without losing case capacity and dropping down to a 260 or the like.

  6. #6

    Default Action

    what kind of action are you planning on using?
    " Americans will never need the 2nd Amendment, until the government tries to take it away."

    On the road of life..... Pot holes keep things interesting !

  7. #7

    Default Cases

    Consider this. A 284 win. case has almost the same capacity as a 30-06 verses the 308 case of the 260. SO, even if you seat your bullet a little deep the case capacity will still be greater and give you an increased velocity over the 260 or 6.5 swede. YOU only loose about 2 or 3 grns of powder capacity but gain about 300 fps over the swede.
    " Americans will never need the 2nd Amendment, until the government tries to take it away."

    On the road of life..... Pot holes keep things interesting !

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    Member RainGull's Avatar
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    I really would like to do it on a Mark V or A-bolt. From what I have read the problem is that the longer bullets start to seat on the ogive.

    I could use the saum case and shorten the case a little (which would improve the efficiency anyways), but that would be more work than fun.

  9. #9
    New member George's Avatar
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    Default 140 in 6.5

    Good question about bullet intrusion into the case body. I can't remember the source but it was a reliable one based on lab testing... but at some unpredictable amount of intrusion, depending upon the cartridge design and components used, where the base of the bullet seats into the case body, normal, expected pressures begin to go squirrely. With the 140gr bullet in the 6.5-284 I can see how this could happen. For example: if a 140gr 6.5 Nosl. Partition bullet is seated into a 6.5-284 to a depth of the maximum length of the parallel bullet shank, the OAL length would be about 2.770. That would leave about .432 of the bullet intruding below the case neck/shoulder junction. Forget the powder capacity, velocity, etc., I too would begin to worry about squirrely pressures with that much. With a short action, if the gun has a long enough mag and the chamber is reamed where the throat length was set for a 140 gr. normal bullet then it may be possible to seat the bullet's base closer to the junction of the neck and shoulder- the ideal place in any instance. But then it would not be set up very well for the 120-125 grain bullets with the relatively short neck of the 6.5-284. It certainly is always a juggling act!

  10. #10
    Member RainGull's Avatar
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    Default

    Let alone the 160 grain Sierra makes!

  11. #11
    New member George's Avatar
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    Default super long 6.5s

    Dya think! My suspicion is that those 160s and in many cases even the 140s were really never meant to be used in the 2.8 inch short actions. The extreme BCs and SDs of many long bullets are tempting but mostly impractical with certain action lengths. The listed BC and SD for the 6.5 125gr. Nosler Partition are .449 and .256 respectively... as a comparison to other bullets and calibers.

  12. #12
    Member RainGull's Avatar
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    Yeah, I think the 160's are funny. I figured they were meant for the Carcano or Arisaka or Swede. Not sure the historical background but I picture them in an WWII cartridge.

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    Default seating depth

    I have found that seating bullets down below the neck/shoulder junction in hunting loads or full power target loads causes a ring to grow at the base of the neck leading to tight chambering after as little as 3 reloadings. Even after outside trimming the cases don't last very long before the neck gets work hardened and cracks along the neck/shoulder junction.

    not trimming this outside diameter could cause the case to squeeze lock the bullet and be the source of the pressure problems discussed earlier in a previous post.

    If brass cost and brass life are not a problem for your wallet go for it.
    Otherwise it may be best to put that puppy in a longer action.

    jedi.

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