Answer to throat measurement?????

rockton

May 20, 2003 08:33

I have read all you have to do is reverse the bullet in a dummy cartridge and insert in chamber.

Remove and measure the overall length to determine length full caliber diameter will contact lands and grooves.

This seems ok to me but I am not sure.

You reloaders can tell me if this will work or not and if not why.

Thanks

Rockton

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  Der Gebirgsjager

  May 20, 2003 09:06

  Yes, that will work. A cerro-safe chamber cast will also work, as the throat is plainly visible on the cast. I've never bothered to try it your way though; I've always placed the bullet point forward in the case and gently closed the bolt, carefully removed the cartridge and measured for overall length with that bullet. The ogive of the bullet is in contact with the lands and grooves at the back of the bore unless the throat is abnormally long. You then want to back off just a little on seating depth to let the bullet get a little start when it begins to leave the case; starting dead up against the lands will raise pressures. But, yes, your method would determine just how long the portion of the throat is that is "full caliber".

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  MrGnA

  May 20, 2003 12:22

  You are really hitting three measurements here, the chamber length, the leade and the OAL.
  Determining chamber length is distance from the head to the chamber where the leade starts. This distance is measured to gain a precise measurement for trimming brass and determining headspace.
  Determining the OAL is the distance from the head to the tip of the bullet. Taking it one step further is a measurement from the bullets ogive to the rifling lands.
  Determinining the leade is the area of no rifling between the chamber and the beginning of the rifling lands.
  The tools are rather inexpensive, problem being once you confirm such measurements, you're unlikely to ever do again.
  
  Your rear-wards seated bullet scheme will work, but there are too many variables involved for inconsistant measurements. If the bullet does not squarely hit the rifling you will get a bad reading, If the bullet is forced into the case easily you will get another and if the metalic make-up of the bullet is soft, you will get yet another.
  See what I mean??
  
  Try to borrow a friends.
  
  
  
  email me at bill@ArmChairHunter.com

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  brayhaven

  May 22, 2003 09:05

  I've gotten consistently good accuracy by just seating the bullet way out until it gets rifling marks just barely visible on the bullet, then cranking the seating stem in a half turn or so & that's the depth for that bulet. This is assuming nothing dumb has been done like Weatherby free-boring.
  GS

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