Bullet seating and pressure changes

[Timo Turl]

Hi,

Let's say I've found a promising node for my load/rifle and work on tweaking that until I've found the optimal load.

After that, I understand it might make sense to experiment with bullet seating depth or using a OAL tool try to measure my rifle's headspace and back off the recommended amount.

My question is does seating the bullet with a small jump to the lands materially change pressure and how does pressure change as you back off more ? Finally, is my "node" constant irrespective of where I seat the bullet and not impacted by this experimenting with seating depth ? Thx

 

[desertHK]

Re: Bullet seating and pressure changes

You have two things to remember when playing with the seating. You have the chamber pressure and the case pressure. Exceeding either one is not recommended.

When you seat the bullet longer, the case pressure goes down. Once you seat it too long and the bullet is jammed into the lands, then the chamber pressure goes up. Either condition is not optimal if you are operating at the peak of your powder curve.

Best thing to do is to measure the chamber length and then seat the bullet accordingly and see which would give you the best group.

 

[Victor N TN]

Re: Bullet seating and pressure changes

Personally I perfer to work with the seating length BEFORE I get to the MAX powder charge. Starting everything when the bullet is either touching or very close to the lands can cause a sharp pressure spike.

I know... It only lasts for a nano-second. Or another VERY short period of time. If it lasted any longer it would be a grenade.

Think a lot and read before making any sudden changes.

Good luck.

 

[Timo Turl]

Re: Bullet seating and pressure changes

Thx Victor. Does variation in chamber pressure impact MV ?

I was thinking about finding my optimal seating depth and then working up to find the appropriate charge as you say but that is contrary to what many have written here. As is said above the case pressure will decrease if i seat long but the chamber pressure goes up.

Assuming you start with the the min loads for the bullet/powder combination could the increase in chamber pressure be dangerous at the min load level and if you seat long are you likely to fall below the min pressure required in the cartridge which i understand is also non-advisable ?

I'm just trying to understand whether it is really right to find my optimal load and then work on seating depth. Assuming changes in seating depth impact MV then presumably the nodes move around and the initial findings of say a ladder test become dated and need to be re-done ?

 

[vman]

Re: Bullet seating and pressure changes

TJ. have a go at loading to mag length and see if you can get some good results like that...

BUT it has been proven that bullets that are seated just in front of the lands tend to shoot better.

TJ. read this article

http://bulletin.accurateshooter.com/2010...lassic-article/
http://www.angelfire.com/ma3/max357/houston.html

In it you will find evidence to suggest that bullet seating depth does play a role in accurate and precise ammunition and that in general seating in front of the lands almost always helps.

Having said that I have the hornady tools and have determined my seating depth to be right in front of the lands. After that I then went over my ladder test again, or you could even try OCW, what ever works for you.

 

[Greg Langelius *]

Re: Bullet seating and pressure changes

Cartridge pressure curves are a long and heated discussion. Without going there, I'll simply say that anyone who knows the subject well enough to completely understand it has managed to escape my acquaintance.

I don't, and I deal with the issue(s?) by trying to keep things on the simpler side.

First, I don't think additional complexities, like pressure spikes, are helpful. I'm fairly convinced that seating into the lands may or may not aid accuracy, but will more likely generate pressure spikes, so I usually don't.

Then, when all other development stages are done, I will experiment with OAL and things like seating into the lands. If it helps, so be it.

Greg