Hydro Arbor Press Bullet Seating Pressure Consistency

[Goes_Bang]

So I've just started using my new 21st century hydro arbor press and inline seating dies. I've never used an arbor before, and I had a question about seating pressure consistency I was hoping someone could clue me in on.

The context.

• .223 Rem
• Wilson Inline micrometer seating die.
• Berger 80.5 gr Freebores.
• Lapua Brass
• Non-neck turned brass.
• Full Length Sized on a Forster with a custom honed -4 thou under neck sizing die, and then a 21st century mandrel up to -2 thou for neck tension.
• Seating to a 10 thou jump off lands. Id have to check my notes, but off the top of my head this was a OGIVE of about 1.91.

What I've noticed is, that I get pretty consistent neck tension for the first 3/4 of the seating travel. For the last 1/4 of the seating travel in the inline die however, the seating pressure necessary drops off significantly. The bullet "feels" well seated at the end of the travel, but the inconsistency in seating pressure (with seating pressure being so light at the last 1/4 of travel) seems odd to me. So, the question is: Is that normal when seating on a arbor? Or am I doing something wrong in case prep?

Thanks!

 

[skeeljc]

How deep are you seating the bullet? In other words what length of the bullet is inside the case?

 

[Goes_Bang]

Well I'm not sure how to measure that accurately, but I can probably get it analytically. (Never looked into this calculation before, but I'll give my math skills a go.)

223 COAL 2.376
223 OGIVE is 1.921 at lands, and I'm jumping 10 thou, so I'm seating at a Ogive of 1.911.

Trimmed case length is 1.75.

Berger website says 1.091 bullet OAL for the 80.5's, but I'm measuring ~1.082 on this lot (P810).

So. 2.376 COAL - 1.75 Trimmed Case OAL = 0.626 of bullet extrusion.

1.082 bullet OAL, - 0.626 = the bullet being seated 0.456 into case.

 

[Dusty Stevens]

Just put a loaded round point against a straightedge and lay a bullet next to it touching the same point. All they want to know is if the pressure ring goes past the neck

 

[PigButtons]

Let me take a stab at this.
To the OP: When the bullet is seated, is the base of the bullet down past the neck of the case? If it goes past the last edge of the neck and into the shoulder area it is no longer "pushing" the neck open and therefore the seating pressure will drop dramatically.

 

[Goes_Bang]

Here ya go.

 

[Dusty Stevens]

Yep you can see there why the force goes down

 

[Goes_Bang]

Care to elaborate? I'm a fairly new at rifle reloading.

Also is the seating pressure observable "bad"? Does something need to change? I loaded to what most people recommend as the typical jump, for my barrel, using this bullet profile.

Thanks again!

 

[jvw2008]

Once the base of the bullet bearing surface passes through the neck/shoulder junction, the bullet is no longer expanding the neck during the seating process. Seating the bullet deeper requires less pressure to make it move.

 

[Goes_Bang]

Ahh thank you, that explanation makes sense. I assume that since this is just a function of the expander portion of the bullet passing out of (the bottom of) the neck, that nothing else as far as the load or neck tension is impacted? (Or to put it another way, there are no other con's to seating this bullet, that deep?)

Thanks for the help!

 

[skeeljc]

The bullet is reducing the case volume but I am not sure that is a con. Pressures will be higher than with a bullet seated further out but you need a chamber with more freebore to do that.