Thread: Brass length trimming question

I recently brought some peterson 280ai brass, it was all very uniform and all measured at 2.5190 or there abouts before firing.
I just deprimed and amp annealed and then sized with a Redding full length die and checked lengths, some were as long as 2.5520 is having to trim .75mm normal?

Unfortunately I didn’t measure any after they had been fired before I sized them. I thought maybe the die could have been stretching them with the button on the up stroke? Especially after being annealed and a bit softer?

I will measure some before and after firing next time.

Only some are long, maybe 75% need trimming, maybe 20% need up to 30 thou taking off.

Just wanting to know if I’m worried about nothing!
Cheers

FYI I set my trimmer at 2.5250

measure headspace, size then measure headspace again... that should tell you if the button is stretching them.

I bought some PPU factory ammo to use the brass for reloading, it all needed trimming after firing the factory load.

Just found a fired one, measured, sized and measured again, it grew 20 thou!
I might invest in a bushing die.

Robh500, make sure you lube inside the case mouths and also rub a bit of lube on the sizing button. You will notice the difference.

Originally Posted by robh500

I recently brought some peterson 280ai brass, it was all very uniform and all measured at 2.5190 or there abouts before firing.
I just deprimed and amp annealed and then sized with a Redding full length die and checked lengths, some were as long as 2.5520 is having to trim .75mm normal?

Unfortunately I didn’t measure any after they had been fired before I sized them. I thought maybe the die could have been stretching them with the button on the up stroke? Especially after being annealed and a bit softer?

I will measure some before and after firing next time.

Only some are long, maybe 75% need trimming, maybe 20% need up to 30 thou taking off.

Just wanting to know if I’m worried about nothing!
Cheers

Greetings Robh500,
Contrary to popular belief it is the full length sizing itself that makes the cases longer, not the expander button. Setting the full length sizer die to just size the case enough to chamber with slight resistance will reduce the stretching. The new cases are always a looser fit in the chamber as they have to chamber in all rifles. It is also harder to make cases as uniform with the 40 degree shoulder on the AI. By all means lubricate the inside of the neck, as I do, but this will not stop the stretching if the case is being over sized in the FL die. The above steps should reduce stretching to a minimum as will neck sizing in a bushing die.
Regards Grandpamac.

Full length sizing analogy –

Get banana. Peel banana. Hold banana upright in right hand, fingers circling (a banana, not your....), place palm of left hand under right, gently squeeze banana (this is what a full length sizing die does to the case walls). Which way does the banana go. Apart from some banana oozing out around your fingers, it goes up/gets longer, same as a cartridge case does when full length sized.

For the cack-handed ones amongst you, just grasp banana with left hand......

Originally Posted by robh500

Just found a fired one, measured, sized and measured again, it grew 20 thou!
I might invest in a bushing die.

measured headspace or oal?

If you have any fired but unsized cases, measure the length on those. Brass will grow during firing as well.

Thanks for all the info guys. Will lube my necks a bit better and look at minimal sizing, I’ll need to measure headspace.

Originally Posted by robh500

Just found a fired one, measured, sized and measured again, it grew 20 thou!
I might invest in a bushing die.

Thats excessive. New Peterson 280ai I have here is 2.520 . Fired 2.526 Resized with minimal shoulder bump 2.525. What was the length of the fired case before sizing?
Have you checked headspace ( base to shoulder) before and after sizing? to confirm correct sizing die set up? Does the sized case chamber easily or is there some resistance closing the bolt?
I agree with @grandpamac but in this case Peterson brass is a little thicker in the neck than others , its possible that over annealing making the neck and shoulder to soft combined wiith the thicker neck might allow the button to stretch it. Just a slim possibility though. A simple test would be to remove the button with your current set up , size the case and see if it still grows.
I personally wouldn't bother annealing new brass on the first firing. For 95% of shooters the benefits of annealing every time are overstated. Im up to the third firing on this Lot with no drop off in ES or accuracy at all and my 243ai is over 10 with lapua brass. A lot of variables.