Below shoulder loading...

[Demi-human]

As to preserve the conversation of another thread...

Are there benefits or detriments to loading bullet bases below the shoulder junction?

Many of my Demi-Average rifles are not capable of anything else with some bullets, however, I am wondering what some ideas about the issue are.
I am of the mind that having the base below the shoulder, very far past the shoulder in some AR compatible cartridges, is not the best for rawest precision.
That the pressure of the combustion could tweak the bullet from one side, or the shank could be deformed asymmetrically is my rationale. As well as the differing tension from seating before, at, or below the junction.
And I like long barrels and speed, so eating into the “engine” compartment is not ideal to either.

What are your experiences? Does it matter? Does it only matter in the strictest of Benchrest processes? Is it immeasurable?

I have my notebook, let’s start class!

 

[Nature Boy]

Are there benefits or detriments to loading bullet bases below the shoulder junction?

Potentially detrimental to accuracy as a donut can form at the shoulder junction resulting in neck tension variations if you seat a bullet into that area

 

[243winxb]

Some factory brass comes with a donut.

When the primer fires, some powder is burned. The rest of the powder is pushed forward to the bullets base or into the shoulder. Bullets below the junction do not seem to be an issue.

The donut is more an issue for tight neck chambers. The goal is to have each loaded round exactly the same.

When the bullet leaves the neck & neck expands, depends on other factors. Mostly a mystery on firing.
Some government studies are interesting. Search here https://discover.dtic.mil/

 

[edwardware]

Other than gas-checked lead bullets, I've never worried about seating bases below shoulders. I also use expander balls and have never had a doughnut.

I am aware that precision rifle can suffer from seating the major diameter below the case neck, but I haven't been able to measure the effect, and I think that jump to lands matters much more.

 

[243winxb]

https://www.ampannealing.com/articles/42/annealing-under-the-microscope/ Photo credit.



The donuts in some 223/5.56 brass has made it almost impossible to pull the expander out of the case neck. The lube didnt help when using RCBS standard dies.
Annealing may help, but i mostly dont.

What does defeat the donut is outside neck turning or a bushing die that doesnt size all the way to the shoulder.
But its best to do both, because the unsized part of the neck expands to chamber after a few firings & centers the rounds in the chamber.

The bushing should not size a fired case down more then .008" More is said to cause run out. (Redding). Sizing the neck down in 2 smaller steps may help.

Its possible to use my standard RCBS 223 dies with neck turned brass. Case life has been longer in a bolt gun. Almost eliminated split necks.

 

[Demi-human]

So the increased neck tension caused by the thickened brass changes the pressure or release time of the bullet.

I imagine if it was thick or strong enough it could damage the bullet base as well.


But what of the deeply set bullet?

Say our brass has been turned. There is no shoulder donut.
The ogive is just at the case mouth and there is no gap to catch.
The case we are using is cavernous and there is power to spare.
Our bullet is long and tolerant of jump distances.

Would just being seated deeply in the case play any role in the accuracy?


(Thank you to @Varminterror for the picture that illustrates my thoughts.)

The reason I ask, beside that I don’t know, is that on the base of some of my recovered bullets I find small pock marks that were not on the perfectly polished bases before. They are the same size and shape as the gunpowder I use. I believe it is from the primer blasting the powder forward as, @243winxb says, so hard it impresses the base of the bullet with texture.
This particular bullet doesn’t extend past the shoulder, but makes me wonder of one that did.

As it sits in a rifle chamber, on its side, does the powder get packed evenly around the bullet before being turned to plasma? Or, like the snow I’m glad to be rid of, does it pack in underneath? Could it then push the bullet to one side as it fires? Bend it even?
Is the bullet pliable enough to do that? Does it get re-straightened from the throat and we don’t even know?

I suppose that if one is already crunching powder it wouldn’t move much.


What I need is a high speed video radiography machine.
I need to shoot a rifle with X-Rays while it is being shot, while shooting video...

I was hoping someone may have some insight otherwise, instead of investing millions of fantasy dollars into technology that does not exist yet.

Wait. Does that technology exist yet, @Odd Job?

 

[Varminterror]

I can’t say I believe I shoot well enough to tell the difference, although I do expect the difference likely doesn’t reveal itself how most folks might expect - BUT - I was told many years ago by one of the guys mentoring me into 600/1000yrd BR that a bullet hanging into the case, below the neck/shoulder junction, is squeezed out more like a tube of toothpaste, rather than pushed out as if by a ram rod. This was in the context of shooting 300wm’s with their incredibly short necks and throats with heavyweight bullets - pushing the base of the bullets WAY down even as far as below the body/shoulder junction. A guy can run quickload analysis to determine the peak pressure to which the sides of the bullet are exposed and model how that may distort the bullet, but a guy can also speculate several influences such pressure patterns can create.

Enough top end bench guys live by it for me to believe there’s at least some real influence, but naturally, testing is a challenge. Running short vs. long COAL would require either two identical barrels, or require reaming a new throat, which in both cases, a significant multi-variable experimental design flaw is present. So testing the theory is largely impossible.

I do expect the difference is far more visible in a 20-40 round group than in a 3-5 shot group, especially so in the hands of a “I pulled that one” shooter.

 

[fguffey]

Again: I have cases that will never form a donut, I also have cases that will form a donut by design and I form cases for some chambers that form donuts before I ever get a chance to take them to the ranger. 'Donuts', that is a subject I am not allowed to talk about. That does not prevent me from fixing them.

On some chambers the case never forms a donut, on cases for other chambers there is nothing I can do to prevent them.

F. Guffey

 

[Demi-human]

that a bullet hanging into the case, below the neck/shoulder junction, is squeezed out more like a tube of toothpaste, rather than pushed out as if by a ram rod.

My thoughts, too. Whether I read them or heard them somewhere, that was what I was wondering about.

Enough top end bench guys live by it for me to believe there’s at least some real influence, but naturally, testing is a challenge.

Especially so with the nice, but still factory, rifles I have.

I do expect the difference is far more visible in a 20-40 round group than in a 3-5 shot group, especially so in the hands of a “I pulled that one” shooter.

I am gradually moving out of that.

I think that I am a far way from being able to use bullet deformation as an excuse, but these things still intrigue me.

I am not quite ready to rent a throating reamer yet, but definitely feel the bullet pressure ring (?not the base, but where the boattail ends.) pass the shoulder junction with more force than the rest of the seating. It’s good to know I’m not completely off base.

Thanks for the reply!

Thank you kindly for all the replies, gentlemen.

 

[fguffey]

In the old days a few of use increased the length of the chamber neck and extended the throat. And then we formed 300 Weatherby cases to 300 Winchester cases with long necks. One of those rifles belongs to a reloader in Garland, Texas, for performance he would not trade the rifle for a Weatherby with a Weatherby chamber.


F. Guffey

 

[fguffey]

I built a 30 Gibbs, the Gibbs has a case neck length of .217". Most 30 Gibbs cases were formed from the 30/06 case. Forming 30 Gibbs cases from 30/06 cases shorten the case by .040". I understand the 30 Gibbs gets longer from the shoulder to the case head, I also understand the ability of the case neck to hold a bullet is reduced.

The neck on the 30 Gibbs is shorter than the neck on the 300 Win Mag by as much as .051" +/- a few.

F. Guffey

 

[243winxb]

As it sits in a rifle chamber, on its side, does the powder get packed evenly around the bullet before being turned to plasma? Or, like the snow I’m glad to be rid of, does it pack in underneath? Could it then push the bullet to one side, as it fires? Bend it even?
Is the bullet pliable enough to do that? Does it get re-straightened from the throat and we don’t even know?

Yes, bullets can be pushed or are allowed to get out of alignment on firing.
The tight neck chambers are designed to keep bullets in alignment with throat/bore on firing. A bullet jammed into the rifling is also good in Benchrest for alignment.

In the 243, one should never (imo) shoot a 55 gr bullet if the bullets base leaves the case mouth before the bullet is aligned in the bore. The loss of alignment is bad enough, but this also allows hot gas to blow by the bullet, before bullet can seal the bore.

When necks don't expand on firing in standard chambers, minimum shoulder bump, , accuracy is better. But necks should most always expand with normal loads & always with factory ammo. The 243 with 70 gr bullets & IMR4350 will not expand my unannealed brass till i get to near maximum pressure.

Working up a load for a 8mm x 57 with a well used barrel shot ok , till higher pressure expanded the case neck to the chamber. Accuracy went away when case necks expanded. When using 4895, loads do not need to be near maximum.