Seating depth and pressure

sdupontjr

WKR
Joined
Oct 8, 2019
Messages
630
I am by no means an expert but do understand, so I think, of how seating depth effects pressure.
So please correct me if any of this sounds waaaayyyy off.

1) a bullet close or into the lands, depending on if close to max load, can and will produce pressure signs. Bullet doesn't get a running start so peak pressure is hit immediately. I would think either backing off powder or seat deeper into case would resolve issue.

2) backing off the land with same charge could produce lower pressures. Bullets has a little wiggle room for jump so pressure is slightly drawn out rather than instant. Sounds good in my head.

3) I would also assume there is a middle ground between too close to the lands and seated too deep in the case. Bullet impedes powder column, even though there is say .120" jump, but compressed load would cause pressure.

4) I have some WW brass, RP, FED, Nosler, Hornady. Mostly RP by a large portion and good bit of WW. The WW brass holds more grains.
So, is it safe to say that I will have less pressure given the same parameters of powder charge, seating depth in WW brass when compared to the RP?

5) what is meant by velocity = pressure? I do have a Garmin but mainly just record my velocities for


I hate to be asking all these questions, just trying to understand. I have been loading for several years now, but want to expand my knowledge because my son wants to get involved.
 

EdP

WKR
Joined
Jun 18, 2020
Messages
1,401
Location
Southwest Va
What you have described matches what Bryan Litz says in his book "Applied Ballistics for Long Range Shooting." Your description in 1 and 2 is exactly the effect that Litz describes. Pressure goes down once there is adequate jump but then goes back up as a deeper seated bullet effectively reduces case capacity.
"Velocity = pressure" means that velocity goes up with pressure.

I think the answer to 4 is yes, the WW case would have less pressure than the RP with the same charge. That doesn't mean the pressure signs would necessarily show because brass hardness also plays a part in observable pressure signs on a fired case.

The seating depth vs pressure relationship Litz describes is what I have observed, but not everyone on Rokslide agrees. Litz is the head ballistics person at Berger Bullets, a well respected ballistics expert and long range shooting competitor. I tend to lean in his direction.
 
Joined
Mar 16, 2021
Messages
3,570
Location
Western Iowa
What you have described matches what Bryan Litz says in his book "Applied Ballistics for Long Range Shooting." Your description in 1 and 2 is exactly the effect that Litz describes. Pressure goes down once there is adequate jump but then goes back up as a deeper seated bullet effectively reduces case capacity.
"Velocity = pressure" means that velocity goes up with pressure.
This is my understanding as well.
 
OP
S

sdupontjr

WKR
Joined
Oct 8, 2019
Messages
630
What you have described matches what Bryan Litz says in his book "Applied Ballistics for Long Range Shooting." Your description in 1 and 2 is exactly the effect that Litz describes. Pressure goes down once there is adequate jump but then goes back up as a deeper seated bullet effectively reduces case capacity.
"Velocity = pressure" means that velocity goes up with pressure.

I think the answer to 4 is yes, the WW case would have less pressure than the RP with the same charge. That doesn't mean the pressure signs would necessarily show because brass hardness also plays a part in observable pressure signs on a fired case.

The seating depth vs pressure relationship Litz describes is what I have observed, but not everyone on Rokslide agrees. Litz is the head ballistics person at Berger Bullets, a well respected ballistics expert and long range shooting competitor. I tend to lean in his direction.
Man, that's good information. I'll have to look into that read.
 
Top