Shoulder bump and group size

[L.Sherm]

You won't feel .001 of resistance chambering a round without a stripped bolt not sure if you would even feel .002

 

[CharlieNC]

Over the years there are many reports that results when blowing out the shoulders to form an improved version (Ackley, etc) give just as good accuracy vs formed, such extreme examples make you wonder about all of the fuss.

 

[L.Sherm]

Fireforming AI cases or like a Dasher are done majority of the time either jamming the bullet into the lands or false shoulder there for not creating alot of Headspace.
The fuss is what the target tell you thats all that should matter wether its .002,-.005 bump or whatever testing will tell you what matters.

 

[L.Sherm]

My theory and take it for what its worth is if your target is .002 bump and now you decide you need .005 have you essentially changed your CBTO? I think so, if your not in the middle of a decent wide seating node is it gonna blow out, I believe it will if your not

 

[dellet]

My theory and take it for what its worth is if your target is .002 bump and now you decide you need .005 have you essentially changed your CBTO? I think so, if your not in the middle of a decent wide seating node is it gonna blow out, I believe it will if your not

CBTO will be exactly the same.
Jump/jam will change.
As will load density, ever so slightly

 

[swd]

LR world record holder Donovan Moran and I talked about shoulder bump. He said he liked .002-.0025" and would take .003" over any less. With anything less you took a chance of spring back and if you have a slightly tight case thats the one that will go out of a group. I tested slightly tight against .0025-.003" and about 50% of the time a slightly tight case will go out of group.

 

[Janeau]

I would suggest that there is no on target benefit to this approach. If anything it detracts from smooth operation and gun handling can suffer.

You obviously not shooting Benchrest…

 

[L.Sherm]

CBTO will be exactly the same.
Jump/jam will change.
As will load density, ever so slightly

I agree on jam but does the bullet release from the neck on a jump bullet before the case hits the chamber shoulder?
Wouldn't that change the CBTO allowing the case to move forward more?

 

[L.Sherm]

Maybe splitting hairs its just my theory for what its worth.

 

[dellet]

I agree on jam but does the bullet release from the neck on a jump bullet before the case hits the chamber shoulder?
Wouldn't that change the CBTO allowing the case to move forward more?

Depends on if you believe the case has to have support for the primer to ignite.

If CTBO is cartridge base to bullet ogive, then you can place the shoulder any where you want and the measurement won’t change.

The neck will get longer or shorter, and the same for body.

Jump/jam is the distance form shoulder to land. If the bullet is set to touch and you move the shoulder back .002”, you have a .002” jam. Move the shoulder the other way ant it pulls the bullet away.

 

[jelenko]

You obviously not shooting Benchrest…

Right.
Not everyone on Accurate Shooter is a benchrest shooter.

 

[L.Sherm]

I dont know, I always go off the theory for every action theres a reaction.

 

[JFrank]

Right.
Not everyone on Accurate Shooter is a benchrest shooter.

Stop talking crazy !!

 

[Wolfdog91]

I have simplified my AR brass sizing by using an ammo checker for setting the sizing die. My winter hunting ammo must drop in to the lower step minimum (0.001 below the step is my target). I don't want ANY loading/unloading live round issues, especially critical when temps are below zero(and at night). I have not had any issues with brass life/separation and I have started to use that die setting for my bolt gun ammo too(mostly prairie dog ammo) for 3 different rifles. When I drop check new brass in the ammo checker(Lyman) all have been several thousands below the lower step and with a comparator are 0.005+ shorter than my sized brass. My KISS and reliable method.

When you say ammo checker you talking about one of those lil cylinder deals you slid your case in to see if it's flush on the end right ?

 

[AlNyhus]

You obviously not shooting Benchrest…

Jim is a UBR world record holder. He tests extensively.

 

[jimmymac]

You obviously not shooting Benchrest…

And you are clueless about me. Apparently I do it different than you. You should continue to do whatever works for you. I know what works for me and that includes ample shoulder bump.

I knew when I made my first post in this thread it was probably a mistake even though my intent was good.

 

[M-61]

I knew when I made my first post in this thread it was probably a mistake even though my intent was good.

Me too. Just deleted all I wrote.

 

[dellet]

I dont know, I always go off the theory for every action theres a reaction.

Maybe I misunderstood the original statement/question or am just having a brain fart.

If you measure from the base of the cartridge, to any point on the bullet, tip or ogive, then move the shoulder, the distance from base to original point on the bullet does not change.

What does change is shoulder to the bullet ogive and base to shoulder. The headspace relationship. Base to bullet ogive remains constant. Headspace changes causing the bullet to change distance to the lands when the cartridge is all the way forward in the chamber.
It would remain the same if the case head was against the bolt face.

As far as the bullet moving forward in the neck before the cartridge touches the chamber, or the neck expanding to release the bullet, is kind of pointless. Because the primer won’t ignite to create the pressure needed to do either unless fhe case is supported enough to allow the firing pin to set off the primer. No different than not seating the primer and having a failure to fire. Or excessive headspace to the point of a light strike. Until there is enough resistance of the primer moving and whole case moving forward and stopping, the primer won’t go off.

I have actually played with this and most primers need a cartridge to weigh about 400 grains before there is enough pressure or resistance that the primer will go off with an unsupported case. Yes you can set off a 9mm in a 357 magnum chamber if the cartridge weighs enough.

 

[jimmymac]

Me too. Just deleted all I wrote.

Sucks. It is better when I just read and not participate. I am wasting my time defending myself for nothing more than bringing a different perspective for people to think about.

 

[Bottom Fodder]

Ok let me get this straight some of you can tell on paper the difference between one thousand and 2 thousand shoulder bump or let’s say a mixture of both.