Shoulder bump question

[huntoregon]

I have 115 pieces of once fired Hornady 7PRC brass I'm getting ready to work up a load with. They were all fired out of the same rifle which is mine. After I knocked the primers out and tumbled the brass I got ready to run through FL sizing die. I measured several with my comparator and the length to the shoulder from base varied as much as .005"

So my questions are: Is this normal? And with that much variance how would you accurately bump the shoulder when they aren't the same to start with?

 

[Luckyshot7]

What size comparator gauge are you using?
I have found that using too SMALL of a gauge (AKA measuring too close to the neck) yields misleading, inconsistent measurements

 

[huntoregon]

.420"

 

[Mikecr]

You need to take your brass to chamber baseline before bumping (before correction).
Fully fire form cases 3 times without body sizing. Find among them a case providing zero headspacing. Set your body die to bump ~2thou. Run all cases through that setting, and always measure each.
Within another firing or two they should all exactly match. Toss any that don't by then.

 

[Dave in WI]

I don't always consider bumping the shoulder after the first firing. If I do, measure the longest case and bump from that. They may not all be fire formed to your chamber yet.

 

[cdherman]

You need to take your brass to chamber baseline before bumping (before correction).
Fully fire form cases 3 times without body sizing. Find among them a case providing zero headspacing. Set your body die to bump ~2thou. Run all cases through that setting, and always measure each.
Within another firing or two they should all exactly match. Toss any that don't by then.

I don't always consider bumping the shoulder after the first firing. If I do, measure the longest case and bump from that. They may not all be fire formed to your chamber yet.

If you need a third opinion, then I'm behind these fellas. They are correct. You will sometimes not fully size to the chamber with the first, second or for that matter many firings. Depends on the load, the brass etc. This is why people get by with neck sizing. At some point most brass fired multiple times and just neck sized will exhibit issues chambering. But not all. If someone never anneals and the brass has some spring back and the loads are modest, you can neck size for a long time. Till you get split necks from lack of annealing or you are sick of poor accuracy because of variable neck tension........

I discovered the issue you are reporting years ago -- was like hey, why all this variation? Your brass is not fully blown out to your chamber.

But -- its probably a lot more blown out than it was as virgin brass. So my process with once fired brass is to deprime, anneal, tumble, and lately Lee collet resize, followed by a Sinclair mandrel, using graphite as lube. This avoids need for more lube removal.

But you can also neck size, or set to "try" and bump the shoulder. Whatever. Just find your process and DON'T vary it often. Learn your process and vary it only in increments. Too many changes at once, you never know what screwed things up or made a meaningful improvement.

 

[overinfinite]

A little reminder that the shoulder is typically going to grow 0.020"+ depending on the chamber and cartridge. I've noticed hornady brass will sometimes fully form in a singular firing. But better brass will typically take 2 atleast.

 

[Koda_]

So my questions are: Is this normal? And with that much variance how would you accurately bump the shoulder when they aren't the same to start with?

It can take 2 or 3 firings, set your die from the longest measurement. It might even grow another thou on the second or 3rd firing. Eventually the shorter ones will catch up. Annealing will make things more consistent.

 

[ranch manager]

I have 115 pieces of once fired Hornady 7PRC brass I'm getting ready to work up a load with. They were all fired out of the same rifle which is mine. After I knocked the primers out and tumbled the brass I got ready to run through FL sizing die. I measured several with my comparator and the length to the shoulder from base varied as much as .005"

So my questions are: Is this normal? And with that much variance how would you accurately bump the shoulder when they aren't the same to start with?

As everyone has pretty much alluded to there are so many variables in brass(especially not top tier stuff). I'm realizing this now as I'm using star line for a 243 Ackley instead of ponying up for Peterson. As any case I let my brass tell me what it needs on how it feels chambering in my rifle and adjust accordingly. For informational purposes I have some certain Hornady 308 tap ammo that won't fire in my 308 because there are up to .020 differences in case dimensions.
These kinda things are actually the part I enjoy because I'm learning and will have data in my memory bank or notebooks for nuances down the road.

 

[Cheez]

It can take 2 or 3 firings, set your die from the longest measurement. It might even grow another thou on the second or 3rd firing. Eventually the shorter ones will catch up. Annealing will make things more consistent.

Fireforming requiring a multi- shot process is a concept that had never occurred to me (not sure why) but I can see huge implications for the various Ackley Improved brass I load a lot (.223, 25-06, 6.5-06.) I've used the "cream of wheat" method in the past on the '06's, but stopped because it was obvious to the naked eye that some of the shoulders weren't blown out fully. Lately, I've been using full-power loads jammed ~2 thousandths because I've been able to get a very accurate, and useful, load that way, while also creating the AI brass as a byproduct. It's like having two rifles - with the ability to alternate at will, and even use factory ammo. (I'm shooting Savage actions, so can tweak headspace easily.)
Seems like this makes a strong case for annealing before fire forming. Do you guys with experience in this find that a fully annealed shoulder reaches its final shape in one firing?

 

[KNOTFERSAIL]

Maybe this has been said and I missed it….but here's what I do

Measure and find the longest one and see if it chambers easily/smooth, if it does don't bump it, or any brass shorter than it. Because obviously there is more room to "grow" before needing to bump the shoulders.

FL size and chute'm again.

If the longest one doesn't chamber bump it .001 or two at a time until it does and set your die there.

Eazy peazy

 

[nksmfamjp]

I have 115 pieces of once fired Hornady 7PRC brass I'm getting ready to work up a load with. They were all fired out of the same rifle which is mine. After I knocked the primers out and tumbled the brass I got ready to run through FL sizing die. I measured several with my comparator and the length to the shoulder from base varied as much as .005"

So my questions are: Is this normal? And with that much variance how would you accurately bump the shoulder when they aren't the same to start with?

Sounds like you are saying FL Sizing variation is your issue.

.420"

That is the right size.

I see it posted that it takes 2-3 firings to form to my chamber. IME, cases are pretty tight after 1 firing. I could probably get 1 more firing on 99% of them, but really need some bump for them to all be easy feeders. I also find that my fired cbtd number isn't changing on a fired case over time.

Back to your issue. Are the fired cases different CBTD measurements or only after sizing.

Variations after sizing are usually caused by sizing lube application and secondarily a need for annealing. Early in the process, annealing is not usually very important.

 

[Alibiiv]

I have 115 pieces of once fired Hornady 7PRC brass I'm getting ready to work up a load with. They were all fired out of the same rifle which is mine. After I knocked the primers out and tumbled the brass I got ready to run through FL sizing die. I measured several with my comparator and the length to the shoulder from base varied as much as .005"

So my questions are: Is this normal? And with that much variance how would you accurately bump the shoulder when they aren't the same to start with?

I am just curious if you are annealing your brass prior to your fire-forming? If not this could be what is causing the .005 thousands variance that you are asking about. In my experience I have not ever found that much of a variance in my fire formed cases. The 7PRC is there in pressure so you ought to have gotten a good fire forming. If I were experiencing what you have described, I would first anneal the brass. From there I would measure all my brass, find the longest piece and bump that shoulder back .002 thousands and remeasure what you have. I anneal everything, including new brass, before I reload. I fire form for a .270 AI, first by the COW method then with a full pressure load. I do not really get a true fire formed cases until after that second firing on the brass. Hope this helps.

 

[huntoregon]

Sounds like you are saying FL Sizing variation is your issue.


That is the right size.

I see it posted that it takes 2-3 firings to form to my chamber. IME, cases are pretty tight after 1 firing. I could probably get 1 more firing on 99% of them, but really need some bump for them to all be easy feeders. I also find that my fired cbtd number isn't changing on a fired case over time.

Back to your issue. Are the fired cases different CBTD measurements or only after sizing.

Variations after sizing are usually caused by sizing lube application and secondarily a need for annealing. Early in the process, annealing is not usually very important.

The fired cases vary prior to sizing.