Is there any Downside to a 40* Shoulder ?

Discussion in 'Reloading' started by 300magman, Jul 7, 2011.

  1. 300magman

    300magman Well-Known Member

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    I am planning to have a couple of barrels chambered for rounds that have 40* shoulders, one is a 22-250AI and the other is a custom dimensioned 7mm short mag.

    I am just wondering if there is any downside to the 40* shoulder. On the plus side it is giving me more case capacity, and brass that will not grow very quickly. But is there any trade off or things to beware of with a shoulder this steep?

    BTW, this is in a precision rifle where cases will have the necks turned, be fireformed, and then only be neck sized inbetween firings. No full length sizing is likely to occur...at least I can't forsee a reason for it.
    Would I ever have to bump the shoulder back??
    (I'm still new to reloading)
     
  2. J E Custom

    J E Custom Well-Known Member

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    The 40o shoulder does two things well. It helps case volume and tends to help with case life
    over the 30 o and down shoulders.

    If you use the neck shoulder junction and go from 30 to 40o you gain very little but
    if you move the shoulder junction forward and go to a 40 o shoulder you can make a difference
    in capacity.

    In some cases it can cause feeding issues but they can be overcome most of the time.

    I Tend to like the 37.5 o shoulders because they feed good and you give up very little case
    capacity.

    Where they are used in single shot actions they are fine and dont have a down side.

    J E CUSTOM
     
    Last edited: Jul 7, 2011

  3. Trickymissfit

    Trickymissfit Well-Known Member

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    I don't remember who the original poster was on this board, but he made a comment about the 40 degree shoulder seeming to produce the dreaded doughnut sooner than the 30 or 35 degree shoulder. I did dissagree with him, and later on did a check with a bunch of empty case. The boy was right! I did some more checking with a bunch of 30 degree cases, and they were better (still a few had it). I honestly have no more plans on doing any 40 degree shoulders if I can get out of it.

    Now the 22-250 basic case is well known for it's brass flow, as well as splitting necks (I associate the two together). Have never bothered to build a 22-250AI, as I watched several of my friends do them over the years, and I got a first hand glimpse into what else happens. Case shrinkage during fire forming is quite a bit (around .04" - .045"), and I think much of the neck splitting is due to all the wall and neck movement during fire forming. I shoot the 6/250AI (very similar, but necked up to 6mm), and you can forget the grand scheme ofusing factory 22-250 brass. Better off using .243 Winchester brass from the start. Most of my friends that still shoot the 22-250AI case now use generic .243 Win. brass. They seem to get better cases after fire forming.

    The 40 degree shoulder is a pain to form, unless your fire forming. A 35 degree shoulder is a little easier, but the 30 degree shoulder is fairly easy. There is a 22-250 improved round that uses a 30 degree shoulder, and another that's made off of the .243 case with a 40 degree shoulder. The latter has a .30" neck length, and is known to push a 63 grain bullet in the 3900fps area.
    gary
     
  4. Coach Hunt

    Coach Hunt Well-Known Member

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    Howdy Magman,
    Just a few comments from my experience with 40 degree shoulders.
    1) brass flow is reduced somewhat, neck length trimming is reduced

    2) yes, powder capacity is increased; however, this is a miniscule increase!

    3) yes, the doughnut is very prominent in this shoulder angle. My personal opinion is that this is because MOST of the cutters on neck turners do not have the 40 degree angle built into the shoulder side of the cutter. Sinclair and Forster will custom grind your cutter to this new angle, or supply you with a new one for a minimal charge. When I switched over to this cutter, the doughnut problem thankfully went away.

    4) annealing the cases is MUCH, MUCH more critical with a shoulder angle this severe. I use either 550 or 650 degree Tempilaq... 550 one caliber down from shoulder, and 650 right on shoulder... and spin the cases in a torch flame then quenching immediately in a bucket of cold water. Without this annealing every 3 shots or so, case neck life will be very short!!! especially with heavy loads.

    Hope this helps, its just what I've discovered over the years working with wildcats and such.

    Best to you and good shooting.

    Coach
     
  5. Mikecr

    Mikecr Well-Known Member

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    All the basic reloading issues and poor approaches aside, there is no REAL problem with 40deg shoulders.
    Use good reloading brass.
    Have a good fireforming plan.
    A good sizing plan..
    Do a little research & enjoy the benefits of it.

    No reason to split crappy factory brass, or trying to form it with FL sizing.
    Don't trim the brass, if possible, until it's fully fireformed. Anneal before fireforming..
    Basic stuff
     
  6. djtjr

    djtjr Well-Known Member

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    Good advise here only real issue I have had is feeding from a mag
     
  7. 300magman

    300magman Well-Known Member

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    Would I be likely to find a reamer for the 22-250 AI that uses a 37.5* or 35* shoulder?

    Other than calling as many reamer manufacturers and smiths as I can find phone numbers for, to see if anyone has one....is there an easier way to search for such a reamer?
     
  8. Trickymissfit

    Trickymissfit Well-Known Member

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    have never seen a 37.5 degree reamer for the 22-250. There are several improved 22-250's out there besides the Ackley. The Shannon uses a 35 degree shoulder with .020" taper in the case. This one according to Ackley shows very little growth in the shoulder area (doughnut). Then there is the Durham Jet that uses .243 cases with a .30" neck length and a 40 degree shoulder. I know of one that uses a 28 degree shoulder, and another that uses a 30 degree angle.
    gary
     
  9. J E Custom

    J E Custom Well-Known Member

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    You are right Gary ,The standard shoulder on most AIs is 40o and if your going to pay to have a
    reamer cut you might as well have it cut the way you want. (It cost the same) Dies are another
    issue. You can make them yourself of have them made.

    If single loading then 40o is not a problem but can be in a repeater.

    I would say If you want less than 40o and can find a set of dies to match what you want,
    that would be the easiest way to go.

    J E CUSTOM
     
  10. ken snyder

    ken snyder Well-Known Member

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    The concerns are feeding and can require modification of the feed ramp, The mouth of the brass likes to catch on the sides of the internal ramp. on stagger feed wells one side will pop out the cartridge to soon and the other side too late. donuts are a very real concern but easily taken care of with an adjustable hand ream. Adjustable reams are available at machinist supply store for under 20 dollars, The adjustable ones give you the option of removing the donut before or after sizing and the same for correcting the problems of moving brass around. reisizing dies can be made with the same ream that cut your chamber but dies made from a casting of your chamber either by your ream guru or custom die manufacturer are better. p.s. take your brass with you while you purchase your reamer and make sure that the pointed pilot end can be filed off short enough that the parrallel section will go past the shoulder neck junction.
     
  11. Trickymissfit

    Trickymissfit Well-Known Member

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    lately I've kinda gotten on the 35 degree bandwagon with large diameter cases, but they still don't run thru a forming die all that well. Also looking back and doing some serious thinking about it; I don't know if the 40 degree shoulder angle is the main reason for the doughnut problems, but I do think it sorta amplifies the situation. Reason I say this is when I look at Weatherby mag cases, I don't see it much. They will run anywhere from 44 degrees to nearly 48 degrees when CAD'd out. I kinda have the feeling in the back of my head that it's the sharp shoulder with the small radius at the neck and case body stopping the flow of brass right at the weakest point.

    what do you think?
    gary
     
  12. ken snyder

    ken snyder Well-Known Member

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    TRICKYMISSFIT, I think your observation is correct. I think the rest of the story is the ring left by the origional neck shoulder junction being moved. And by the neck wanting to shove down into the shoulder from the less supportive shoulder angle. In any case its an easily corrected problem but can be a continual annoyance.