What Is Seating Depth???

rahtreelimbs · December 24, 2006, 10:06 PM

While I have been reloading and using seating depth as a method, what it does escapes me. Is it that changing the depth times the bullet's exit out the barrel to keep it in the same position on the barrel's whip?

Rimrod · December 25, 2006, 12:41 AM

To start with it allows the cartridge to fit in your magazine. Each cartridge has a maximum Overall length and gun manufacturers use this when they design the firearm.

Seating the bullet where it almost touches the lands of the barrel improves accuracy but may also force you to load the rounds one at a time if the OAL is longer than the magazine.

On the other hand there may be an instance where a particular bullet will have to be seated deeper. Such as using certain cast bullets in a revlover, but this will also increase pressure so it must be done very carefully.

amamnn · December 25, 2006, 02:11 AM

In ye olden days we referred to the length that the bullet was run out of the case as runout. These days, people use runout as a sort of generic term for misalignment of various components in a cartridge. So now we're stuck with the term seating depth which is a backward way of describing how far in or out of the case you've left your bullet when you are done loading the cartridge. You want your bullet seated in the neck far enough in that you can maintain proper tension (the grip of the case neck upon the bullet) on the bearing surface of the bullet. Unfortunately for those who want to use the popular benchrester's method of seating the bullet out to the lands of the barrel, factory rifles have chambers that make the method largely ineffective if not impossible.

If you have the knowledge and the tools to measure the chamber of your rifle and the base to ogive length of your bullets, and head to ogive length of your cartridges, you'll have a good idea of how far out you need to seat in order to approach or get into the lands of the barrel. Most times, just going for long seating without ensuring concentricity (alignment, or runout) of the neck inside and out and the chamber/barrel of the rifle results in no improvement as the bullet has to bounce around to find the center of the lands.

Without controlling the above variables, long seating is mostly just guesswork and if you get a real improvement it's mainly luck.

Bullet94 · December 25, 2006, 05:23 AM

Quote:

Is it that changing the depth times the bullet's exit out the barrel to keep it in the same position on the barrel's whip?

I assume your talking about rifles.
I believe seating depth effects pressure and also effects the barrel vibration (whip). I believe your trying to fine tune your load to where the bullet leaves the barrel at the optimum time in the vibration or oscillation to produce small groups. So the short answer I believe would be yes. I’ve read that it takes a rifle capable of shooting in the ones to get much out of seating depth changes (for fine tuning) and that most rifles do best at mag length or into the lands (if they are capable).

December 24, 2006, 10:06 PM	#1
rahtreelimbs Senior Member Join Date: December 8, 2005 Location: Pittsburgh Pa. Posts: 195	What Is Seating Depth??? While I have been reloading and using seating depth as a method, what it does escapes me. Is it that changing the depth times the bullet's exit out the barrel to keep it in the same position on the barrel's whip?

December 25, 2006, 12:41 AM	#2
Rimrod Senior Member Join Date: October 19, 2005 Location: Behind enemy lines Posts: 1,309	To start with it allows the cartridge to fit in your magazine. Each cartridge has a maximum Overall length and gun manufacturers use this when they design the firearm. Seating the bullet where it almost touches the lands of the barrel improves accuracy but may also force you to load the rounds one at a time if the OAL is longer than the magazine. On the other hand there may be an instance where a particular bullet will have to be seated deeper. Such as using certain cast bullets in a revlover, but this will also increase pressure so it must be done very carefully.

December 25, 2006, 02:11 AM	#3
amamnn Senior Member Join Date: May 13, 2006 Location: WA, the left armpit of the USA Posts: 1,323	In ye olden days we referred to the length that the bullet was run out of the case as runout. These days, people use runout as a sort of generic term for misalignment of various components in a cartridge. So now we're stuck with the term seating depth which is a backward way of describing how far in or out of the case you've left your bullet when you are done loading the cartridge. You want your bullet seated in the neck far enough in that you can maintain proper tension (the grip of the case neck upon the bullet) on the bearing surface of the bullet. Unfortunately for those who want to use the popular benchrester's method of seating the bullet out to the lands of the barrel, factory rifles have chambers that make the method largely ineffective if not impossible. If you have the knowledge and the tools to measure the chamber of your rifle and the base to ogive length of your bullets, and head to ogive length of your cartridges, you'll have a good idea of how far out you need to seat in order to approach or get into the lands of the barrel. Most times, just going for long seating without ensuring concentricity (alignment, or runout) of the neck inside and out and the chamber/barrel of the rifle results in no improvement as the bullet has to bounce around to find the center of the lands. Without controlling the above variables, long seating is mostly just guesswork and if you get a real improvement it's mainly luck.