Brass is shrinking after annealing...

[cscott0708]

I measured the shoulder (Hornady comparator) on fire formed brass to see how much the brass moved when fired, this was with once fire brass. I then annealed the brass; Bench Source annealer, double flame set on the heck to shoulder junction, dwelled in the flames until neck just started to turn red. Brass was set aside for FL resizing the next evening. Twenty four hours later I begin the FL die setup (Reeding deluxe FL die), measured the shoulder and noticed it now measures .003" - .004" less than before annealing. This is with 300 RUM Norma Brass.

I ran a separated batch last weekend for a different gun, but still 300 RUM with ADG brass. The process was; measure brass, anneal (same annealing setup as previously described), and 1.5 hours later I resized using Imperial Wax. I measured the shoulder and it was the same as before annealing. I completed the resize operation (same Reeding FL die in a Forster CoAx press) and loaded up my loads. I had 15 pieces of brass leftover as I ran out of bullets in that box. For comparison to the Norma brass that "shrunk" I measured the ADG brass that was annealed and resized 5 days ago and they are .006" under the initial shoulder bump back??? I know for certain I bumped the shoulders back .0025" as I measured the first 5, measured half way through to ensure it was in-control, and the last 3 and all had a .0025" bump back.

I'm fairly new to annealing, so is this normal?

I've reloaded (hunting only) for 40 years and just recently being to load precision ammo and it has made a drastic difference in downrange performance. I watched a lot of videos and read a lot data on annealing and do not recall anyone saying that the shoulder dimensions will change after annealing.

Thanks,

Chris

 

[Straightshooter1]

I measured the shoulder (Hornady comparator) on fire formed brass to see how much the brass moved when fired, this was with once fire brass. I then annealed the brass; Bench Source annealer, double flame set on the heck to shoulder junction, dwelled in the flames until neck just started to turn red. Brass was set aside for FL resizing the next evening. Twenty four hours later I begin the FL die setup (Reeding deluxe FL die), measured the shoulder and noticed it now measures .003" - .004" less than before annealing. This is with 300 RUM Norma Brass.

I ran a separated batch last weekend for a different gun, but still 300 RUM with ADG brass. The process was; measure brass, anneal (same annealing setup as previously described), and 1.5 hours later I resized using Imperial Wax. I measured the shoulder and it was the same as before annealing. I completed the resize operation (same Reeding FL die in a Forster CoAx press) and loaded up my loads. I had 15 pieces of brass leftover as I ran out of bullets in that box. For comparison to the Norma brass that "shrunk" I measured the ADG brass that was annealed and resized 5 days ago and they are .006" under the initial shoulder bump back??? I know for certain I bumped the shoulders back .0025" as I measured the first 5, measured half way through to ensure it was in-control, and the last 3 and all had a .0025" bump back.

I'm fairly new to annealing, so is this normal?

I've reloaded (hunting only) for 40 years and just recently being to load precision ammo and it has made a drastic difference in downrange performance. I watched a lot of videos and read a lot data on annealing and do not recall anyone saying that the shoulder dimensions will change after annealing.

Thanks,

Chris

Hmmm??? I've never measured after annealing, so I can't really address that. Though you've got my curiosity going and I'll have to test that and see.

I've not seen any change in base to shoulder datum for any of the various brass I've used (Lapua, Peterson, Federal, Hornaday . . . and many more, but not ADG) after having been annealed and sized. Though I do see changes in neck OD's after 24hrs due to springback from the sizing operation, which amounts to ~.0005".

Wow! .006" is huge and I can't imagine what that might be at work there. I've certainly not seen anything like that with all the annealing I've done.

 

[JMayo]

I anneal first thing. I have measured to know chamber size & annealing didn't change that.

 

[cscott0708]

Yes, I agree .006" is huge, basically back to new dimension.

The annealed shoulder datum dimension did not change after 2 hours, but did 1 and 5 days later.


Not sure what should be causing this...

 

[rijndael]

Do you have a gauge block to verify/test your caliper?

 

[Lucky6547]

What tool are you using to measure? Perhaps there’s an inconsistency in the placement of various parts?

 

[Coyotefurharvester]

Are you quenching after annealing?

 

[cscott0708]

I'm using a new 8" Mitutoyo ABSOLUTE coolant proof caliper and 1 year old 6" Mitutoyo ABSOLUTE coolant proof caliper. Both give the same reading. I have triple checked the caliper and Hornady bullet comparator setup and all is good square fit.

I have not verified the calipers with a gage bock, but I will. I have measured bullets and get a consistent reading to the bullet spec. or with in a few 10,000's. So, I believe the calipers to be accurate enough to be repeatable to within a few 10,000's.

I'm not quenching, just room temp cooling.


Chris

 

[rijndael]

I don’t pay attention to larger caliber stuff, but didn’t Brian Litz recently talk about dimensional brass changes in big calibers that made people use new brass more often?

 

[TTE]

I don’t pay attention to larger caliber stuff, but didn’t Brian Litz recently talk about dimensional brass changes in big calibers that made people use new brass more often?

How big is big calibers ?

 

[AlNyhus]

What would be surprising is if the base-to-datum didn't change. -Al

 

[cscott0708]

Yes, I could see it increasing maybe .0005"-.0001", but not shrinking.

 

[AlNyhus]

If the shoulder is forward due to being hardened, is it so surprising that it moves back after the stress is relieved?

 

[cscott0708]

Yes, I'm surprised it moved that much and very surprised it moved after FL resizing.

 

[Nick Caprinolo]

The human hair is about .04. .006 is so miniscule as to mean nothing. I wonder if it were a wire of that thickness you would even be able to see it.

 

[dellet]

It’s possible that it’s really a diameter change, where for lack of better words, the taper diameter changes at a given length.

 

[Downhill]

Relating this to steel, when heated the molecules spread upon cooling they contract and end up tighter than before heat. Have used this to both camber I beam and straighten pipe after welding. Probably the same effect you see in your brass.

 

[mikecr]

What was the method of annealing?
How far down the case did you go?

 

[big5ifty]

What the brass measures before and after annealing is not important, what matters is where the shoulder is after sizing.

If you get that much shoulder movement after annealing, then if you chamber an annealed, unsized case without the firing pin in the bolt, it should flop closed with zero resistance.

Is that what's happening ?

 

[Rick300]

So if I read this right, you are measuring the shoulder bump after annealing and after resizing? It is certainly possible and almost guaranteed that annealed brass will resize to a different number than non annealed brass. Your .003-.004 movement sounds like a lot, but if your brass was very work hardened then annealed, I could see it changing that much. IF this is the case, then either anneal every time and adjust your die for that, or don't anneal every time and adjust for that. Either way, do it the same every time and I think you're good to go.