Why so much diff in seating pressure needed?

[GetReal]

Here's my set up:

LE WIlson sizing die w/ 0.268 neck bushing
Caliber : 6 ARC
K&M Precision seating press
LE WIlson chamber style bullet seater
Bullets: 90 gr Berger Target

My shoulder set back is nice and consistent, neck I.D. is reasoanble consistent (2-3 thou smaller than 0.243 bullet diameter) ...

SO why does seating pressure vary so much from case to case?

All teh brass was deprimes / cleaned / preppped the same way as a singler batch. Carbon inside the neck s/b faily consistent.

Puzzling.

 

[gunsandgunsmithing]

How many firings? Annealing might help, although I'm not typically an annealer. It does have its place and it might be just what the Dr ordered. If everything else is consistent, that's where I'd look. If annealing isn't a possibility, have you tried new brass yet? Seeing it's an ARC, brass quality from Hornady is not good IME. Probably a factor and annealing may well help but I wouldn't put a lot of work into Hornady brass.

 

[Fuj]

Are you turning the necks ?? Are you annealing ?? Is the bullet
being seated deep enough that you have interference at the neck/
shoulder junction due to some cases having formed a donut ??

 

[Straightshooter1]

Here's my set up:

LE WIlson sizing die w/ 0.268 neck bushing
Caliber : 6 ARC
K&M Precision seating press
LE WIlson chamber style bullet seater
Bullets: 90 gr Berger Target

My shoulder set back is nice and consistent, neck I.D. is reasoanble consistent (2-3 thou smaller than 0.243 bullet diameter) ...

SO why does seating pressure vary so much from case to case?

All teh brass was deprimes / cleaned / preppped the same way as a singler batch. Carbon inside the neck s/b faily consistent.

Puzzling.

A number of things could be a play (e.g. variation in donut size, if it's being touched; variation in chamfering; burrs on some of the chamfered lower part of the cut; variation in the lube of the neck; variation in work hardening of the neck, more so as the number of firings increase, variations in the neck wall thickness; and add any combination of these things). I find it tends to mostly be associated with variation in work hardening from one case to another and this is where annealing can help.

 

[GetReal]

A number of things could be a play (e.g. variation in donut size, if it's being touched; variation in chamfering; burrs on some of the chamfered lower part of the cut; variation in the lube of the neck; variation in work hardening of the neck, more so as the number of firings increase, variations in the neck wall thickness; and add any combination of these things). I find it tends to mostly be associated with variation in work hardening from one case to another and this is where annealing an help.

Forgot to menton...I AMP anneal every firing. But the rest of that is all possible.

 

[RegionRat]

All the above plus... ID chamfer? Anneal or no-anneal? Brush neck ID? etc. etc.

Not only does the brass prep affect the hoop stress applied by the brass to the bullet, but the little details in things like the donuts, ID chamfers, friction coefficients, etc. The seating force is generally the product of the brass forces that apply the pressure times the friction coefficients of the things like the neck ID and the chamfer.

 

[GetReal]

Are you turning the necks ?? Are you annealing ?? Is the bullet
being seated deep enough that you have interference at the neck/
shoulder junction due to some cases having formed a donut ??

Don't turn necks.
Anneal every firing.
Seated past neck shoulder junction

 

[Bill Norris]

Here's my set up:

LE WIlson sizing die w/ 0.268 neck bushing
Caliber : 6 ARC
K&M Precision seating press
LE WIlson chamber style bullet seater
Bullets: 90 gr Berger Target

My shoulder set back is nice and consistent, neck I.D. is reasoanble consistent (2-3 thou smaller than 0.243 bullet diameter) ...

SO why does seating pressure vary so much from case to case?

All teh brass was deprimes / cleaned / preppped the same way as a singler batch. Carbon inside the neck s/b faily consistent.

Puzzling.

have you tried running a mandrel into the necks just prior to seating the bullet ?

 

[Webster]

Here's my set up:

LE WIlson sizing die w/ 0.268 neck bushing
Caliber : 6 ARC
K&M Precision seating press
LE WIlson chamber style bullet seater
Bullets: 90 gr Berger Target

My shoulder set back is nice and consistent, neck I.D. is reasoanble consistent (2-3 thou smaller than 0.243 bullet diameter) ...

SO why does seating pressure vary so much from case to case?

All teh brass was deprimes / cleaned / preppped the same way as a singler batch. Carbon inside the neck s/b faily consistent.

Puzzling.

Check out Eric Cortina's video's on annealing. He annealed for 3 different times and measured the seating pressure. and bump. No consistancy in seating force. No explanation given. Looks like you just have to accept it as normal as long as the gun shoots.

I see many replies listing endless possibilities for seating force variation but they are all guesses. Erik does good brass prep and still sees variation.

Many people talk about avoiding annealing the case lower body. You could melt the case neck and still not soften the case head area. I doubt you could get the lower half of the case above 300-400F and it would cool quickley. It's time and temp dependant. I see where some guys hold the case in their fingers to anneal with a torch and drop it when it gets to hot to hold comfortably.

 

[GetReal]

have you tried running a mandrel into the necks just prior to seating the bullet ?

I've done that in the past but got some negative feedback / responses here as to the practice. SO, not sure what to think...

 

[GetReal]

Check out Eric Cortina's video on annealing. He annealed for 3 different times and measured the seating pressure and displayed the results as a graph. No consistancy in seating force. No explanation given. Looks like you just have to accept it as normal as long as the gun shoots. He did everything to unuform the brass before annealing???

Now that I think about it, I've seen that. Thanx for reminding me.

 

[GetReal]

And of course the $64,000 question....

What kind of difference (if any) is varying seating force making in your groupings?

 

[Straightshooter1]

I've done that in the past but got some negative feedback / responses here as to the practice. SO, not sure what to think...

If your brass has significant variations in neck wall thickness and you just use a bushing sizing die without an expander ball, variations in neck wall thickness will mostly be moved to the inside, which often can be part that issue you're having. Using an expander mandrel afterwards will move most of that variation to the outside and also help mitigate the donut issue to some extent.

 

[6Creed73]

have you tried running a mandrel into the necks just prior to seating the bullet ?

This^^^^^

I Iearned awhile ago that running a mandrel through the necks before seating removed pretty much all seating variance.

When I size my brass ahead of time, I skip the mandrel step until I'm ready to use that brass. It's the last thing I do prior to charging and seating. On the contrary, when I was fully prepping my brass and letting it sit for a period of time, I figured out that the brass was moving...the necks would spring back a bit on some of them. Then when seating bullets, I was getting varying seating depths and could feel pressure differences.

Since doing the mandrel step prior to seating, it's now rare to get seating depth variations more than .0005

 

[fisherman987]

Sounds like you are using unturned necks with a neck wall thickness between .013 and .014. With necks that thick, you are going to get a lot of grip on the bullet. I would go up a thousandth to a .269 bushing and see if you get a reduction in seating pressure and a little more even. Also, if you are wet tumbling your brass, you could be washing too much of the carbon out of the necks. Leave the carbon alone and just give the necks a light brushing.

 

[piie]

If everything else is equal on your brass, then the most likely culprit is uneven neck contact with the bullet. Turning/skimming necks- first pushing uneven brass to outside with a mandrel and then taking off the high spots and evening up neck thickness- will greatly reduce the difference you see in resistance between cartridges

 

[Jager]

Annealing fired brass (as opposed to new) can make inside the necks slightly sticky, as the heat of the annealing process interacts with the carbon residue. You can reduce this stickiness by using a dry lube.

Not sure why running a mandrel would ever cause a problem, other than adding a step that might ultimately not provide any benefit. Hard to see a downside.

And as @fisherman987 describes, you might try reducing your neck tension.

 

[Fuj]

Seated past neck shoulder junction

That will do it every time, considering everything else is spot on.
I use a mandrel, and in some instances, I will inside ream the case,
but only that neck/shoulder junction when forming new brass for
my cats. I also use a Lee Collet die. Some guy's do not like to ream
and will push the donut outward with a mandrel, then neck turn it.

Using any neck lube ??

 

[Brians356]

If neck wall thickness varies within and between cases, so must seating resistance vary, but not linearly or predictably. And the thicker the walls, on average, the more variance.

Also, I usually spin case mouths in steel wool after chamfering, to burnish out any tiny burrs.

I'd also be probing with pin gages to assess donut variation, case to case.
-

 

[Cfshooter]

I do not anneal, but do FL size and size necks about .003 down from mandrel size, dry lube necks, mandrel, then seat. Seating pressure does vary for me, but not by much or too often out of 100 rounds with that process.

When I size necks down to only about .001 under mandrel size, pressure varies more.

As others have said, try not to seat to or past the neck/shoulder junction, donuts lube there.

When I just FL size and dry lube (no mandrel) as I do for my gas guns, the seating depth varies much more.