My brass is shrinking ?

[TC]

New to reloading so plse bear with me. New Lapus brass .308 used in an AI and measured close to the 2.007/2.008 when it arrived. I didn't trim or re-size and shot up to 47g Varget with the 155 Lapua and 45g with the 178 AMAX, max recommended loads.

Case head to datum/shoulder with the Hornady comparator was 1.624 new and 1.626 once fired but case length had shrunk to 2.001 and in some instances even under 2.000. Out of 100 cases, none measured more than 2.007 so they all appear to have shrunk ?

They chambered fine so i reloaded them without trimming and shot the same loads just necksizing (measured and there was no bump so pretty sure i did that right/die was set high). Measurement after second firing is case length still varies between 2.001-2.006 (with a handful still below 2.000) and case head to shoulder unchanged at 1.626 and will still chamber.

So is case length shrinkage normal if you don't overwork the brass and i expected to see gradual growth in case head to shoulder length up to the point where i need to bump it ? Is it that the brass softens each firing and perhaps on the 3rd/4th firing it jumps in length and to shoulder forcing the trim and shoulder bump ?

Given i shot consistent loads and i measured the powder with a redding beam scale i'm also surprised to see brass length varying from under 2.000-2.006 when all bullets were seated to the same depth. I'd be interested in hearing what you think might be happening. I plan to shoot them for a third time this weekend so get another chance to see if the figs change. Thanks

 

[Eddie Harren]

Think about it. When the case body blows out to AI dimensions, at the body/shoulder junction, and the shoulder angle changes to 40 degrees, the case is going to get shorter.

 

[TC]

Ok, so on the second firing when there was no change in the shoulder, why didn't the case get longer ? Is such a large shrinkage in overall case length fairly normal ??

 

[Eddie Harren]

Once the case is fully formed, to the AI chamber, the case should not get longer or shorter, outside the normal case stretching due to repeated firings or, pulling an expander ball through the necks. One of the reported benefits of an AI case is less case stretch.

 

[RonAKA]

Your sizing method can affect growth as well. Neck sizing only results in less growth than FL sizing.

 

[TC]

i see, thank you

 

[artbosco]

So is case length shrinkage normal?

It's very normal. When you neck it up manually it shrinks. When you fireform it, it shrinks. After that you start getting some growth. Monitor for trimming.

Full Length size each and every time you reload and you'll be in good shape. Don't monkey around with half measures of neck sizing one minute and shoulder bumping the next. Full length size all the time for consistent results.

 

[TC]

So is case length shrinkage normal?

It's very normal. When you neck it up manually it shrinks. When you fireform it, it shrinks. After that you start getting some growth. Monitor for trimming.

Full Length size each and every time you reload and you'll be in good shape. Don't monkey around with half measures of neck sizing one minute and shoulder bumping the next. Full length size all the time for consistent results.

Interesting. So are you saying not to believe in the supposed benefits of fireforming and I should just FL size each time ? I actually don't care about "working" the brass and brass life but instead more about accuracy.

I was thinking it will probably take me 3 firings to form my brass. Then I planned to bump the shoulder back a couple of thous below that level each time but i can't do that until it has formed to my chamber. You think that is a waste of time & monkey business ? Thx

 

[Eddie Harren]

I believe what Outdoorsman is suggesting is, that you set your dies up to bump the shoulder a couple of thousandths everytime rather than just neck sizing. If you have a way to measure the bump this can be done.

 

[TC]

I get that but is he suggesting you set those dies up from the very first time you shoot using the brass or once it is fireformed to the chamber concerned ?

 

[Eddie Harren]

There is no way to set the shoulder bump on an unfireformed case, when using an AI chamber. You must first fireform your cases to your chamber.

 

[BoydAllen]

There may be some degree of misunderstanding here. When you posted that you were shooting the brass in an "AI" specifically what were you referring to?

 

[Eddie Harren]

I think Boyd has nailed it. It isn't an Ackley Improved but most likely a Accuracy International. If this is the case disregard all of my posts. I thought it was an Ackley Improved situation. Sorry. Sometimes it takes two whacks, with the brick, to wake me up.

 

[artbosco]

So is case length shrinkage normal?

It's very normal. When you neck it up manually it shrinks. When you fireform it, it shrinks. After that you start getting some growth. Monitor for trimming.

Full Length size each and every time you reload and you'll be in good shape. Don't monkey around with half measures of neck sizing one minute and shoulder bumping the next. Full length size all the time for consistent results.

Interesting. So

are you saying not to believe in the supposed benefits of fireforming If you are a reloader and reloading new brass you should Always fireform. I fireform brass TWICE before taking cases into competition. Fireforming twice is however sufficient.

and I should just FL size each time ? I believe that brass should be full length sized each and every time for consistency. That's the norm in short range BR where I compete. It also ensures you don't over work the brass because it's reformed in minuscule increments of .0005" to .0015".

I actually don't care about "working" the brass and brass life but instead more about accuracy.

I was thinking it will probably take me 3 firings to form my brass. Then I planned to bump the shoulder back a couple of thous below that level each time but i can't do that until it has formed to my chamber.

You think that is a waste of time & monkey business ? I believe working different parts of a case separately at different time intervals is a departure from consistency. I always want a case to be proportioned with chamber dimensions. Consistency, Consistency, Consistency is the name of the game and world that I shoot and compete in.

 

[CJ6]

I'm with you DocEd. I look at AI to mean Ackley Improved not Accuracey International as it pertains to cartridge nomenclature

 

[TC]

Thank you for the replies and advice. Apologies on the confusion, AI = Accuracy International.

 

[matthewusmc8791]

Great thread and I pretty much only read most forums due to the infighting between people and everyone has their opinions and which is best…


My question is, why would you want to full length size EVERY TIME when you fired your round the case is matched to your chamber perfectly..
Why would you want to make it a generic SAMMI spec and sloppy…. That doesn’t make any sense.. Only in a hunting rifle would you want to make the case a sloppy fit for faster reloading..

You definitely aren’t working your brass much if any when you only neck size… Comparing a FL die to a neck die its night and day… FL die your moving EVERYTHING… neck die is just the neck, that’s why they call it neck sizing..
What is more consistent, a case formed to your chamber or some FL die regardless of who made it, it’s made to SAMMI specs it’s not made to your chamber. So when your FL sizing your brass, you are starting AL OVER EVERYTIME..
Why on earth would you want that…


3 fire forming… Are you crazy, must have endless supply of bullets, powder, and primers, not to mention TIME…. You load 40+ grains of Varget, in that case it will expand to your chamber and your set….
You’re going to be practicing anyways, so each time you shoot it, it will become more chamber sensitive.. but you’re not going to have to fire it 3x for that to happen…


Why would you have to bump your shoulder back if you never plan on using that brass in another rifle, the brass is formed to your chamber, its perfect for you..


Good luck.