Skip to main content
Help Center Community Shop

throat or freebore?

Geri
I see the usage of throat and freebore used with the same meaning. I was told years ago that the throat was the amount the bullet could be seated before it touched the bore. Freebore was the removal of the rifleing lands for a certain distance, but the bore diameter was not changed. Any input welcome, and thank you.
0

Comments

5 comments

Date Votes
  • cody45
    freebore is the amount of the bore, ahead of the throat, absence of rifling lands. free bore allows the bullet to "jump" out of the case before engaging the rifling resulting in higher velocity. this idea is usually credited to Roy Weatherby and his propietory line of magnum cartridges. this idea is fine for big game hunting but is not conducive to the best accuracy. Bench rest shooters always strive to chamber their rifles with the minimum of feebore so the bullet actually touches the rifling when fully chambered. factory chambers are usually a compromise.
    0
  • modoc
    Freebore in shotgun barrels also allow smoother flow of shot which in turn lessens felt recoil.At least that is what the experts claim. I for one, ream all older shotgun barrels to be safer,that insures length enough to open the folded crimp compared to the roll crimp that most older guns were chambered for.Have fun second,safety FIRST.

    BILL
    KEEP YOUR POWDER DRY.BUT NOT HOT.....single action S&Ws are keepers
    0
  • nononsense
    Geri,

    You've got it sort of correct. Here is a drawing of a chamber.

    308W-Lager.png

    The area marked G1 is the "freebore" which is also referred to as the leade. The freebore is a straightline cylindrical space that does have the lands removed but it is usually a pinch bigger than the bottom of the groove. The diameter is approximately 0.0002" to 0.0005" larger in diameter than the groove diameter. In this description of a .308 Win. it means that the freebore diameter would measure 0.3082" - 0.3085" depending on the specification by the buyer or SAAMI. The length of the freebore is variable also, from 0.000" to 0.500" to allow for a pressure decrease or the seating out of extremely long VLD bullets.

    The throat is marked 'F' in this drawing. It is the tapered area directly in front of the freebore (leade). This is the area that provides the transition of the bullet from freebore to land/groove contact. It acts like a funnel, easing the bullet into the lands. The most generic taper used is 1 degree 30 minutes, but as in this example, there can be many different ones ground onto the reamer.

    Best.
    0
  • Geri
    Thank you all for the info. I was told about a 22 rf target rifle that had no rifleing till the last 6" of the barrel. I was told that this was freebore, and the bullet (lead) was forced into the smooth bore to provide true alignment with the bore. Some what the same as the old Pope target rifles. Thanks again.
    0
  • nononsense
    That sounds similar to the breech seating method used by some target shooters. The lead bullet is seated into the bore first, in alignment, and then the cartridge, with a wad of sorts to contain the powder charge, is chambered behind and the breech is closed. Not too unlike the the concept used in large naval guns.

    The drawing above though, is the modern explanation of leade (freebore) and throat.

    Best.
    0

Please sign in to leave a comment.

Recent Activity