Throating ?'s

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by TheBlackPearl, Oct 30, 2009.

  1. TheBlackPearl

    TheBlackPearl Member

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    Can somebody please explain "throating" a gun for a certain bullet. I'am in the process of building a rem700 300rum maybe edge maybe lapua not sure yet. Have heard alot of people talking about this!
     
  2. RockZ

    RockZ Well-Known Member

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    This is simply setting the chamber/throat up for the cartridge/bullet combo you want.
    Make a dummy round with the bullet you want at the OAL you want and the smith will set up the throat to that spec.
     

  3. Coyboy

    Coyboy Well-Known Member

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    Yep, it's that easy.
     
  4. royinidaho

    royinidaho Writers Guild

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    Jim,

    What about angles to match ogives etc? Does that make any difference or is it even a consideration?
     
  5. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Something you might consider is your reloading technique. Some guys like me, only partial size their neck leaving a doughnut arount the base of the neck which fits snug into the neck chamber. I would have my thoat reamed to accomodate to the bullet I use to be about .010 off the lands and the base of the bearing surface of the bullet to be even with top of the doughnut in the neck. This allows max capacity in the case keeping the base of the bullet from encroaching into the case.

    Hope that makes sense,

    Mark
     
  6. royinidaho

    royinidaho Writers Guild

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    Mark,

    You talkin' to me?

    Yep that's what I do except for the chamber throat part. However I'm going to talk to the smith about that even though I have no shortage of case capacity.

    In my non wildcat chambers I partial neck size on caliber down and take what ever seating depth the chamber gives me. In the/my 338 RUM w/identical powder charges the partial neck size give about 20 FPS less velocity than a FL sized case. Thus I get to burn a little more powder for the same velocity.:rolleyes:
     
  7. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Roy,

    No, I was talking to Black Pearl not you. I figure you probably knew this a lot longer than me. Glad you answered though. What you said about loosing velocity is interesting. I just recently started partial neck sizing but in the past when I've seated bullets to fit the mag and then taken them out about 0.10 or so closer to the lands I noticed both a slight drop in velocity and pressure *with the same load* which I expected. I figured however, that I could slightly increase the load for a little more velocity with close to the same original pressure. It seems to make logical sense to me that increasing the case capacity decreases the powder to pressure ratio and increases velocity when you increase powder. Same principle as *Improving* a cartridge I would think?

    So you used more powder, and got less velocity with the same pressure?
     
  8. Coyboy

    Coyboy Well-Known Member

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    Roy, most sammi spec factory chambers and reamers have a lead angle of 3 degrees, this would be the tapered portion of the cut that makes a "ramp" out of the lands for the bullet to engrave on.

    Almost all "match reamers" will be ground with a 1.5 degree lead angle.

    When a reamer is made the purchaser can spec whatever lead angle they want, and Kiff will grind it. I have a couple of reamers of Aarons design for the 7mm RM that have 3/4 degree lead angles, obviously designed for the bergers.

    So from this description it is apears that the sammi spec for you basic cartriges designed for standard factory ammo have the steepest angle which would better match the olgive of most standard factory bullets while the shallow angles are used with the high bc low drag bullets.

    I think that the bigger factor may be lower initial pressures with the shallower angles, this may well cut down on the engraving force of the bullet to the rifling, I have a few hunting rifles in standard offerings that have the 3 degree lead and they do shoot as well as any.
     
  9. royinidaho

    royinidaho Writers Guild

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    Nope. Found exactly the same as you. Took a bit more powder to achieve the same velocity and pressure with more consistent accuracy. But over all it "improved" the case somewhat and allowed even more powder, pressure and velocity within limits. And I pushed those limits.:rolleyes:
     
  10. royinidaho

    royinidaho Writers Guild

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    Jim,

    Thanks for the response. Kiff is in the process of making me a reamer for the inside shape of a jacket. I'm also considering a bullet design with an "aggressive" ogive radius. I have to learn first what "too" aggressive is.:rolleyes: Some where along the line increasing the ogive radius has got to jump up and bite ya in the butt.

    Also, I see ya over on a mini-lathe board. Ya can't hide from ol Roy:D Darned if HF didn't back order my 7X12 or I'd have the shop feet deep in copper chips already.:D