How do I create a false shoulder?

[C.E.Smith043]

I'm going to try to make this as short as possible.

I'm loading for a 25DTI. The concept is to take a piece of 6.8SPC brass and neck it down to 25 caliber, load and shoot and the 25dti is then formed.

To my understanding the shoulder moves from the parent case of 23° to the new angle of the 25dti of 30°

Do I need to create a false shoulder in order to get this to chamber and fire properly in an AR-15 platform.

If yes, how do I create a false shoulder?

As you can tell, I really don't even know what a false shoulder really is.

 

[jepp2]

Do I need to create a false shoulder in order to get this to chamber and fire properly in an AR-15 platform.

If yes, how do I create a false shoulder?

A false shoulder will hold the case head tight against the bolt face for firing when you fireform your cases. This ensures the shoulder is blown forward to the new shoulder angle. It keeps the case from stretching above the case head which can lead to an incipient case head separation.

I don't know the cartridge dimensions of your conversion, so I can't comment on if you need one or not.

The way you create a false shoulder is to only neck down a portion of the neck, so the unreduced neck diameter stops the case from moving as far forward as if you sized down the entire case neck.

I bought a used Remington that had been rechambered to a 223AI. I could tell by the barrel markings, the barrel had not been set back a turn during the chambering (required to have the proper headspace). I checked the headspace as best I could and could tell it was excessive. I took the fired brass I had with the longest case head to datum measurements, sized them without any shoulder bump (this created a greater case head to datum measurement). Of the 20 cases I fired, 16 showed serious stretched in front of the case head. I sent the rifle to my smith to have it properly chambered. He found the headspace was +0.016" when it should have been -0.004". So the 0.020" excess headspace was sufficient to set the cases up for case head separations. The previous owner had formed the brass using COW.

 

[C.E.Smith043]

A false shoulder will hold the case head tight against the bolt face for firing when you fireform your cases. This ensures the shoulder is blown forward to the new shoulder angle. It keeps the case from stretching above the case head which can lead to an incipient case head separation.

I don't know the cartridge dimensions of your conversion, so I can't comment on if you need one or not.

The way you create a false shoulder is to only neck down a portion of the neck, so the unreduced neck diameter stops the case from moving as far forward as if you sized down the entire case neck.

I bought a used Remington that had been rechambered to a 223AI. I could tell by the barrel markings, the barrel had not been set back a turn during the chambering (required to have the proper headspace). I checked the headspace as best I could and could tell it was excessive. I took the fired brass I had with the longest case head to datum measurements, sized them without any shoulder bump (this created a greater case head to datum measurement). Of the 20 cases I fired, 16 showed serious stretched in front of the case head. I sent the rifle to my smith to have it properly chambered. He found the headspace was +0.016" when it should have been -0.004". So the 0.020" excess headspace was sufficient to set the cases up for case head separations. The previous owner had formed the brass using COW.

Ty so much. That makes sense. I'll do some experimenting and see what I come up with. Thanks again.

 

[Benchrest Braxton]

watch this

 

[Ringostar]

You will need to make sure that the bolt closes all the way with your AR. That could be an important thing if you leave some neck at 6.8 size.

 

[Webster]

A false shoulder will hold the case head tight against the bolt face for firing when you fireform your cases. This ensures the shoulder is blown forward to the new shoulder angle. It keeps the case from stretching above the case head which can lead to an incipient case head separation.

I don't know the cartridge dimensions of your conversion, so I can't comment on if you need one or not.

The way you create a false shoulder is to only neck down a portion of the neck, so the unreduced neck diameter stops the case from moving as far forward as if you sized down the entire case neck.

I bought a used Remington that had been rechambered to a 223AI. I could tell by the barrel markings, the barrel had not been set back a turn during the chambering (required to have the proper headspace). I checked the headspace as best I could and could tell it was excessive. I took the fired brass I had with the longest case head to datum measurements, sized them without any shoulder bump (this created a greater case head to datum measurement). Of the 20 cases I fired, 16 showed serious stretched in front of the case head. I sent the rifle to my smith to have it properly chambered. He found the headspace was +0.016" when it should have been -0.004". So the 0.020" excess headspace was sufficient to set the cases up for case head separations. The previous owner had formed the brass using COW.

I don't see a problem? I FF a 6BR to 6BRX. The shoulder is pushed 0.100" forward. 0.100" excessive head space. Using a new 6BR case I determine the touch distance. Then set the bullets 0.010" jam. This forces the case head against the bolt. Fire a case measure the base to ogive with a bump gauge. If you can size a case with 0.002" bump your OK. Your cases and chambers don't have to meet SAAMI specs as long as you can size it with std dies. You have created a mini wild cat. You pushed the shoulder 0.016" forward. A fired 6BR case will not chamber in my 6BRX, You have to hammer it out. My 6BRX FF small groups. It cost a lot to rechamber a rifle. If you cannot size with a std die it would be cheaper to call someone like Whidden explain the problem and ask if you send a few fired cases can the make a new die or modify your die.

The so called proper head space with go/no go gauges are only for manufacturing purposes. This insures that any ammo you buy in the store will chamber with reasonable headspace. Factory ammo is real sloopy in the chamber.

 

[jepp2]

I don't see a problem?

I understand and agree with most of what you stated. If the rifle had only been for my use the entire life of the barrel that could have been an option.

However, I would never sell a rifle with out of spec headspace. And based on my intended use of the rifle I didn't want to have to deal with what was required. One of the main benefits of an Ackley is that you can fire factory parent round ammo in it. I couldn't. with this rifle.

 

[Coyotefurharvester]

Brass forms better in an AR if you shutdown the gas, hand eject each fired case.