Seating depth changing?

[Huntnful]

Did we ever confirm is OP was getting variable length in COAL or BTO?

If it was in COAL, delete this whole thread…. Hahaha kidding.

 

[Rick Richard]

Not the entire cass just the neck junction. If the brass is expanding 001-.003 at neck why wouldn't their be enough force to also move the neck downward. 001 or so at the same time.
Not saying it would as I haven't measured it. Just a thought.

Not near the force as when resizing and bumping the shoulder, which causes brass movement, but I can't see the amount of force doing that when just seating a bullet. Oh well, thanks for your thoughts….and do respect them.

 

[340 in Va]

Have you seen seating depth change from round to round, when using a seating die? Am I doing something in my process wrong or why would I see a variation of 0.001-0.004 using a Hornady Micrometer seater on a Hornady Custom Seater Die?

My assumption was once set, lock ring tightened, they should all be really close after using my dummy round to verify length with comparator. Ideas? I basically have to check every round right now and am seeing more variability than I'd like, so I just don't trust it. Do you really need to measure every one?

What bullets are you using? Had same problem years ago when measuring col. Measure your bullets, that may be your difference.

 

[Dr. Richard Gray]

Do you trim your brass prior to reloading?
That could be the differences (0.001 -0.004) that your seeing.

 

[nksmfamjp]

Frankly, i would look into your mindset a bit. It seems like you are asking for solutions. Others are providing solutions, but nobody seems to know the problem.

If seating depth in on box of bullets varies CBTO by 0.004", that is normal. If more, how much. If OAL in 1 box of bullets is varying 0.008", probably normal.

The problem is most likely the measuring point and its relationship to the seater push point. Pull the seater and mark the touch point on the bullet. Better yet, spin the bullet with so flitz on it in the seater to fit it. Now put your measurement tool on it and mark its touch point. Different ain't it!

OAL is a more precise measure for you, but there is more variation in the bullet there.

First, try some things. Adjust every seating depth to the same depth. Shoot it and a standard group. I would shoot 2 groups of 20. How do mean radii compare?

This kind of test can b done for many things we "worry" about. Most don't matter.

 

[the bullet man]

Neck tension variability also affect seating depth variability. If one neck it tighter than another, the bullet goes farther into the stem as it forces its way into the tighter neck, making a longer BTO measurement.

You don't need to pull your bullets though, you can't shoot the .004 difference anyways. The rounds in your mag are likely getting bumped more than .004 from recoil when you just shoot your gun.

this right here^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 

[Rotten]

Brass has a certain amount of elasticity to it before it bends. In machining we call this memory. like a spring or bending metal it needs to be bent further than what you want because of spring back.
This is what keeps the bullet in place when seated. Otherwise if it had zero memory like being anneald to dead soft the bullet would fall right out. So if you're expanding the brass outwards by pushing the bullet into the brass it also has to deflect downwards as well. This is why straight wall cartridges get shorter when sized. So to me it only makes sense that there has to be a curtain amount of deflection in the brass downwards as it is being deflected outwards to seat the bullet. That doesn't mean it will stay down it springs back. Will that cause a seating length variances? To me yes if the neck tensions are different you would have a different outcome. Could this be measured by a set of calipers ?
I don't know. Just my 2 pesos

 

[hunterjohn]

Could be from a bunch of different things I had the same problem I'm not sure which 1 solved it but I made sure the trim length was good another thing for me I used steel pins to clean brass and didn't used to use graphite on the necks and my brass wasn't always same number of firings seems the neck tension would vary which would give me inconsistent seating the annealing really help that

 

[skipglo]

You, sir, are apparently not ADHD enough!

I check every single round I load and adjust and seat to within .0005".

Thank Lance for having enough for both of us! You are a good man!

 

[G Arlen Good]

Yep...what they said.

 

[Carlos88]

All good info. The baseline of the bullet is where measurements should be taken IMHO. The Hornady tool I have measures at the ogive which is useless for anyone switching bullet weights or makes. Ogives and lengths vary widely.

CBTBL if you will.

 

[LRNut]

I read all the posts but quickly. No one has mentioned primer seating depth. I discovered this a while ago by trimming cases to the exact same length and then seating using a hand primer. Lapua pockets are tight and I would often get longer measurements simply due to the primer not being flush. I got a CPS priming tool for my CO reloading room and it made a huge difference. I use a hand tool in Az but measure before and after primer seating.

Neck tension most definitely can affect seating depth. You can also get .001 diff simply by the pressure exerted using your calipers.

 

[Alibiiv]

I've read on a couple of post where "neck tension" can effect seating depth…..how so? You are using a ram with WAY plenty of force to seat a bullet with little resistance to a stopping point that can't be exceeded. Thus, traveling a specified distance. Sorry, I just can't wrap my head around this one.

Seat a heavy monolithic bullet in a compressed load and that bullet can/will move out and not necessarily the same amount every time. Annealing will help neck tension to be consistent. A crimp will help prevent the COAL from moving, however the crimp is done "after" the seating process. We're talking .001-.004 thousands here. Unless each and every bullet can be seated and measured individually at the time it is being seated there's going to be some variation.

 

[Rick Richard]

Seat a heavy monolithic bullet in a compressed load and that bullet can/will move out and not necessarily the same amount every time. Annealing will help neck tension to be consistent. A crimp will help prevent the COAL from moving, however the crimp is done "after" the seating process. We're talking .001-.004 thousands here. Unless each and every bullet can be seated and measured individually at the time it is being seated there's going to be some variation.

I do and have experienced variations with "compressed" loads, but NO way will a bullet be effected otherwise by Neck Tension alone. As mentioned, the force of the ram is much greater then the force of Interference Fit……