? on fire forming brass

[brasstacks]

Guys,

I have not had this issue in my time as a reloader and wanted others input. I have a new 280AI that I am working with and the chamber is very very tight. A new Nosler 280AI brass is measuring 2.134 with my head space gauge. I am bumping the shoulders back two thousandths so the measurement is 2.132 and it chambers well with light pressure to close the bolt. After firing the brass for the first time to form it to the chamber I am getting a measurment of 2.130. Not what I was expecting! I expected to see the brass move forward a half to one thousandth. Who has knowledge on this issue?

 

[CaptainMal]

Might your "headspace gauge" not be hitting at a different place on the shoulder?

The AI would have a different angle to the shoulder with your gauge hitting at a different spot then the standard angle shoulder.

 

[brasstacks]

May be possible but I would assume that as long as you are measuring with the same guage then everything should be relative. This new brass was not 280 brass. It was 280 AI from Nosler.

 

[alf]

I think the answer lies in the "light pressure to close the bolt".

Is the Nosler brass too tight to chamber w/o bumping it back two thou?

 

[spclark]

Is the case OAL growing any between new and once-fired? I can kinda imagine a shoulder receding; takes some mental gymnastics compared to the usual experience. Who chambered your new barrel? If you're feeling pressure on the bolt chambering cases with shoulders already pushed back from where the factory set them, I'd be surprised if the shoulders move forward any from there.

Doing a search using 280 AI Headspace I found a few comments elsewhere that the Nosler brass is fairly soft, and that they use the SAAMI specs for dimensions... not the optimum for best fit in an Ackley 280 AI chamber.

http://www.longrangehunting.com/forums/f28/nosler-280ai-brass-general-consensus-58241/

http://noslerreloading.com/phpBB2/viewtopic.php?t=3947&start=0&postdays=0&postorder=asc&highlight=&sid=827cfa16fd962149a0dbe837a217a490

http://gunsmithtalk.wordpress.com/2010/01/13/280-ackley-improved-alert/

 

[brasstacks]

The new un sized Nosler 280AI brass will chamber but it takes way too much effort to close the bolt. Bump it back .002 and it closes like it's suppose with the proper feel. spclark you a are in agreement with me on the on the shoulders moving. If I chamber a virgin piece of brass it has a crush fit in which the chamber will actually bump the brass back half of one thousandth to 2.1335. I bumped the loaded rounds back to 2.132 and upon firing the brass is settling back to 2.130. It is shrinking.

I do know that the brass that Nosler is producing for the 280AI is a SAAMI spec which is actually .oo4 longer that the traditional 280AI that has been wildcatted for years.

 

[coyoteklr]

i would not size the new brass before fireforming.... turn the sizing die to shell holder and back off one full turn....chamfer...... load and fire form.... then do the sizing and measuring and trim to length.....i don't like to mess with anything until i have the brass fire formed..... the only nosler brass i use is for the 22-250 it works well why ... i don't know, but all the rest is way to soft........

 

[jonbearman]

As it forms the shoulder body junction it akmost always pulls the neck back slightly with no trimming necessary.Every chamber reamer has slight differences caused in manufacturing which is no big deal at all.But fire forming forces the shoulder to fill out and draw the case neck back.I shoot 22-250AI and noticed the same thing.What is your real concern? Is it causing problems? Remember that when nosler forms the brass it is way easier to form it than depend on the chamber reamer to be used the same each time and wear occurs on all tooling that is cutting,depends on how hard the barrel steel is and the cutting lubricant etc.

 

[jo191145]

What your seeing is perfectly normal.
You have tight headspace or long virgin brass. Thats fine.
The rest of the brass is not so tight in the chamber. Upon firing it expands to fill the chamber. This allows your shoulders with tight headspace to move back off the chamber for a fraction of a zillionth second as the brass is drawn backwards/outwards reducing headspace minimumly.

Once the brass has fully filled the chamber (including the shoulders) you'll see the normal springback which is your fired case measurement.

I'd say your chamber is a perfect example of crush fit fireforming. I set all my chambers up in that fashion. Just don't get too carried away with hot loads until the brass is once fired. Crush fit fireforming does add stress on your lugs and action.

Judging by your measurements of fired brass at 2.130" if you set your FL die to bump back 2.129" that would give you .002" headspace. I like less , thats just an illustration of where you should be at in terms of cases vs chamber fit.
Quite possible to see some variation in those numbers too. Slight differences in shoulder angles between virgin brass, fired brass and sized brass can throw numbers off a hair. They should always be close tho.