Fire Forming: False Shoulder OR Seat in the Lands?

[Wheres-Waldo]

How much excess headspace is TOO much for fireforming an AI case?

Im forming 6.5x47 Lapua AI from its parent 6.5x47 Lapua.

Here is the schematic of a 6.5x47 Lapua AI chamber with a .292" Neck

And here is a 6.5x47 Lapua chamber (Pacific Tool & Gauge #9205 reamer with a .160" free bore and a 1 1/2 degree throat angle)

We can see there is a difference in headspace of .0049"
Could I seat bullets hard into the lands for fire-forming, or would I be safer creating a false shoulder on the neck for this? I'll be turning necks anyway, as this chamber requires it.

 

[ChadTRG42]

Re: Fire Forming: False Shoulder OR Seat in the Lands?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wheres-Waldo</div><div class="ubbcode-body">We can see there is a difference in headspace of .0049" </div></div>
Not really! That's way too busy to read.
Either one will get you to the same spot. If you seat the bullet slightly (not hard) into the lands, you don't have to size the brass before you fire. If you feel like sizing them first with a larger expander ball, and then to the AI die, it works too, just one more step. I'd probably fire form them with some cheap bullets and mild charge.

 

[Wheres-Waldo]

Re: Fire Forming: False Shoulder OR Seat in the Lands?

LOL, I hear ya Chad....

Well, I hear that if you have a decent bit of difference between the parent case and your chamber, seating into the lands can cause the case to slip foward a bit during primer strikes, which wont leave you with good results.

I'll probably wind up crating a false shoulder...depends on how big of a PITA it is. Trying to imagine how I could measure the position of a false shoulder....

 

[wnroscoe]

Re: Fire Forming: False Shoulder OR Seat in the Lands?

For our Dashers we use the false shoulder method. We expand the neck on our 6BR brass with a .257 expander and then resize the neck in steps with a bushing die until the brass will just chamber in the Dasher. Jamming bullets is OK but the false shoulder method is rock solid and brass is ready to go after FFing

 

[Wheres-Waldo]

Re: Fire Forming: False Shoulder OR Seat in the Lands?

Thanks Roscoe.

Could I create that shoulder when I'm neck turning by only turning down far enough to chamber, and have that unturned portion be my false shoulder....?

Im kinda relying on my brass to have thick enough neck walls to be able to do that, but if they do, it seems easier.

 

[C.K]

Re: Fire Forming: False Shoulder OR Seat in the La

If it were me I'd create a false shoulder and fire form with pistol powder,cream of wheat and a pwad. I wouldn't waste powder or bullets.