Throating a rifle barrel

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Driller54, Jan 5, 2012.

  1. Driller54

    Driller54 Well-Known Member

    Messages:
    84
    Joined:
    Jun 29, 2011
    Alright guys I got one for y'all! I've been reading around and have cought on to a few people cutting the throats of their barrels a little longer in order to seat vld style bullets further out in the case allowing for more powder charge in the case and so on. My question is with the throating how much is enough how much is too much or would I consult the person doing the cutting. I would still like the rounds to fit inside the magazine box.
     
  2. Michael Eichele

    Michael Eichele Well-Known Member

    Messages:
    3,829
    Joined:
    Jan 6, 2003
    1 way to do it (assuming you have a competent smith) is to take your smith your rifle and a 'dummy' round seated to your desired length. Short enough to feed smoothly and long enough to maximize powder capacity. Tell him how far into or off the lands you want the bullet and he should get you close. I find .015-.020" shorter than the box mag inside dimension allows for smooth feeding.
     

  3. rscott5028

    rscott5028 Well-Known Member

    Messages:
    2,608
    Joined:
    Apr 18, 2010
    Your reamer mfg can also advise. They sometimes are already familiar with certain popular cartridge/brass/bullet combos.

    With a lot of hot cartridges, you'll end up chasing the throat anyways. So, you may be reducing overall effective barrel life as well as making the rifle not well suited for other bullets.

    Those are just some of the possible trade-offs if you get greedy and try to optimize too much for a very specific purpose. On the other hand, you could hit a home run.

    In addition to what Michael stated, your best bet is to find someone that's already had success with your desired setup and let them replicate the same specs.

    -- richard
     
  4. Rustystud

    Rustystud Well-Known Member

    Messages:
    431
    Joined:
    Dec 25, 2007
    Some helpful hints:

    1. I buy all my reamers with only .020"-.040" freebore. Then I use a piloted throating reamer to cut my throats the desired depth. I suggest no flat based bullet be seated deeper than the necjk shoulder juncture of the case. I suggest no boattail bullet be seated deaper than the rear of the bearing surface at the neck shoulder juncture of the case. Seating bullets back beyond the neck shoulder juncture only ask for trouble with fliers.

    2. When using a piloted throating reamer use a mechanical stop that can be moved for ward incrementally. Throating is only removing the rifling and a sharp throating reamer can cut the rifling out like a knife in warm butter. Rewmember it is easy to remove metal but difficult to put it back.

    3. Remember a throating reamer is cutting a tapered hole and lenier measurment is not the same when cutting in two different planes.

    4. Aslo if you are using a dummy case with a bullet seated make sure the case is sized, trimmed, (measured to minimum spec. Be sure to chamfer and turn the necks a little. Also make sure the case is not contacting in the web area. You are want to measure off the bullet ogive.

    5. clean with a brush and clean patches and air before measuring.

    Nat Lambeth
     
  5. Michael Eichele

    Michael Eichele Well-Known Member

    Messages:
    3,829
    Joined:
    Jan 6, 2003
    What is you theory on this? Or facts for that matter. I mean how have so many of us fired 300 grain SMKs and Bergers out of our 338Edges with such phenominal accuracy and consistency when the boattail/bearing suface junction is WAY down past the neck/shoulder junction? Same has applied to the 208 Amax in various calibers.

    Not arguing, just curious what the reasoning is.
     
  6. msalm

    msalm Well-Known Member

    Messages:
    225
    Joined:
    Jul 18, 2007
    A lot of accuracy minded shooters don't like the bullet bearing surface rearward of the neck shoulder juncture as there can be somewhat of a 'doughnut' at that point and it does not offer the consistent neck tension of a bullet seated forward of that point.
     
  7. Michael Eichele

    Michael Eichele Well-Known Member

    Messages:
    3,829
    Joined:
    Jan 6, 2003
    Maybe with proper neck turning/sizing, this issue could be minimized?
     
  8. Rustystud

    Rustystud Well-Known Member

    Messages:
    431
    Joined:
    Dec 25, 2007
    Michael:

    With long VLD bullets almost all of the shooters begin to experience fliers when bullets are seated back beyond the neck shoulder juncture. This is especially noticed on round 6mm up to 30 caliber. This is why I ask my customers to send me a bullet and dummy round so I can set the seating depth according to bullet length.

    I setting the seating depth for the particular round not the round to the existing seating depth.

    Hope this explains what I am saying.

    This has been established by the F-Class and Long range Benchrest shooters who have fire hundreds of thousands of rounds experimenting. You will always have those who want to jump and those who want to jam their bullets.

    Nat Lambeth
     
  9. Michael Eichele

    Michael Eichele Well-Known Member

    Messages:
    3,829
    Joined:
    Jan 6, 2003
    Nat,

    Fair enough. Do you know WHY this occurs?
     
  10. elkaholic

    elkaholic Well-Known Member

    Messages:
    5,285
    Joined:
    Dec 4, 2008
    Be sure you don't seat it Too far out into the neck either. You need some neck support on the bullet as accuracy can be lost there as well. Usually, this is not a problem if it will fit in the magazine. The mag is quite often the limiting factor if you want a repeater.....Rich
     
  11. rscott5028

    rscott5028 Well-Known Member

    Messages:
    2,608
    Joined:
    Apr 18, 2010
    Are they simply trying to maximize accuracy caused by the "doughnut"? Because, there are other ways to deal with the "dreaded doughnut" if that's the real or perceived cause of fliers.

    Could maximizing case capacity be another issue for serious F-Class shooters?

    -- Richard
     
  12. Rustystud

    Rustystud Well-Known Member

    Messages:
    431
    Joined:
    Dec 25, 2007
    First, I am not an engineer or physist. My theory would be your are dealing with a very long projectile. When the bearing surface is pushed beyond the neck shoulder juncture it allows for the burning gasses to push not just from the rear but from the sides. We all know primers when fired start a forward burning of the powder. we know that those enclsed expanding gasses are moving violently. This conclusion was highly studied by P.O. Ackley as well as the engineers at Picatinny arsenal and other laboratories.

    My theory would be some bullets may yawl as they break loose from the neck engaging into the rifling. Most people think bullets just abs up the bore in a spiral. If one looks at a barrel during firing unter time lapsed photograph and X ray one would see just how violently a bullet moves from side to side until it gets stablized several inches down the bore.

    I give the following example have you ever seen a bearing dropped into a funnel. as it goes toward the center it both speeds up and tightens up its spiral.

    Again I am not an engineeer and this is my theory based on many years of reading and shooting.

    You might broach this subject with Gene Beggs over on the Bench rest Central Web sight he is a wealth of (balistic) knowledge. Another good source might be Al over at Varmint Al's webbsite. He has many computer models of bullets leaving the case and moving down the barrel.

    Nat Lambeth
     
  13. rscott5028

    rscott5028 Well-Known Member

    Messages:
    2,608
    Joined:
    Apr 18, 2010
    Nat -
    Thanks for the insight.
    - richard