seating bullets

Discussion in 'The Basics, Starting Out' started by ISB, Mar 12, 2008.

  1. ISB

    ISB Guest

    Hey pros--Is there a rule of thumb as to the minimum depth a bullet can be seated into the case in referance to the diameter of the bullet--I have read about seating off the rifling , but there has to be some rule out there as to how far out of the case you can seat the bullet and still remain safe and obtain accuracy.? Clear as mud--I hope not---
    Thanks Charlie
  2. royinidaho

    royinidaho Writers Guild

    Jan 20, 2004
    Welcome aboard!!!

    I'm not a pro by any means however I like to talk alot;)

    In factory case, '06, 270, 280 for example, I only resize the neck one caliber from the mouth. Somewhere, years ago, I picked up that idea from someone.

    On the other end of the spectrum, the further the bullet is seated out the lower the velocity and pressure up to the point when the bullet is jammed into the rifling. It may be appropriate at that point to reduce the powder charge a bit.

    Usually, in a sporting rifle, the seating depth is determined more by what will work in the magazine more than anything else.


  3. MagnumManiac

    MagnumManiac Well-Known Member

    Feb 25, 2008
    A good 'rule of thumb' is that one calibre of seating depth,i.e .277 into the case mouth for 270 rounds,but,and this is a big BUT,most calibres larger than .224 won't be able to be seated this way because the bullets are simply too long for this.Case neck length differs from cartridge to cartridge,and this will change seating depths significantly.
    If you are shooting a target/varmint calibre,the above rule will mostly work,and it does in the 22-250,22-250 AI,220 swift and others.
    If it is a hunting rifle you're using,then the magazine length,throat length and length of the bullet will determine the seating depth.
    The 25-06 is a very good example of throat length influencing the seating depth.This cartridge is chambered with so many different throat lengths,even in factory rifles,that there is no 'rule of thumb' for it.
    You simply have to measure where the origin of the rifling touches the bullet in this case,and then back off .020"-.050",or closer,or further,to get the seating depth for EACH bullet style.Reloading manual quoted OAL figures may or may not work in any particular gun.
    I recommend getting one of the bullet comparator tools or RCBS precision mic's,so you can get your bullets seated the correct distance from the origin of the lands.
    Now,seating a bullet so far out of a case so that there is only a very small proportion of the bullet in the case,less than 10% of the length of that bullet,is a very bad idea,for these reasons,the bullet will begin to move at the first instance of the primer detonating,which can cause the bullet to tip because there is insufficient speed to make it 'jump' into the rifling,the neck tension will be so little that ignition in the case is poor,because the bullet being held tightly helps build the correct amount of pressure before the bullet moves in the neck,and lastly,you can end up with the S.E.E (secondary explosion effect) by the bullet jamming in the lands when the primer detotnates,and the rifle turning into a BOMB.
  4. James Jones

    James Jones Well-Known Member

    Jul 1, 2002
    alot of guys like to have at least one caliber size of bullet being held by the neck , like MM pointed out if you have a 30 cal rifle you want at least .300" of bullet BEARING surface in the neck , the boat tail doesen't count as its not touching anything. The reason for this is maximum stability for the bullet to keep it from being knocked out of alignment of falling in or out of the case.
    Some cases , like the 300 win mag have short necks and alot of folks will swear that short necked rifles can't be accurate , thats clearly wrong as a long list of trophies that the 300 win has to its name.

    If your not to rough on your bullets you can seat them out as far as you like to obtain accuracy , the biggest factor is that they are strait , and the farther out they are with less neck holding them the easier it'll be for the bullet to get out of alignment.Some BR shooters (typicaly short range) that use flat base bullets have very little bullet in the neck and the bullets ar not fully seated in the case , the final seating comes when the round is chambered and the bullet is pushed back into the case by the lands , this is called soft seating.

    as for the seating depth , as a general rule of thumb mosty guns shoot with the bullet either just up to the lands or their close to them but guns Like weathery's are the exception as alot of them shoot very well and the bullet is nowhere close to the lands due to the free bore. You will generaly find that you will see pressure signs a bit sooner with the bullets seated into the lands also.
  5. Strick9

    Strick9 Well-Known Member

    Nov 16, 2007
    A buddy of mine was telling me that his mentor which I have yet to meet, lets the gun do the talking here, he uses the action and bolt to push and seat the bullet into the first cartridge , no powder or primer of course...Then uses this cartridge as a guideline for seating all others..Is this suitable? This guy and his equipment are apparently moa out to 1000 all day long..Just curious as to the validity here?
  6. LewisH

    LewisH Well-Known Member

    May 13, 2007
    Yes, that's a well know technique known as a "jam fit." It's used to ensure proper ignition when fire forming "improved" cases from the parent case, and it indicates the max. loaded length for that bullet/chamber.

    Some loads may actually shoot best that way; but it does increase pressure, and the bullet often sticks in the lands when you extract an unfired cartridge (spilling powder throughout the receiver). :mad:
    Last edited: Mar 14, 2008
  7. ISB

    ISB Guest

    Thanks for the info--

    The info I recieved really helps and puts my interest to sleep on this question that has been buggin' me.
    Thanks again---Charlie