7 PRC Brass shoulder measure changing?

[BossGobbler2024]

I got some once fired Peterson brass from a member on here. I measured the shoulder length and then fire formed in my rifle. I got the reading and bumped .002 back. Now I am on the 4 the firing and happened to check the measurement and its now .004 longer than the initial once fired readings I have. Anyone else experience this with their brass? Note I use AMP annealer after every firing also.

 

[swavescatter]

I got some once fired Peterson brass from a member on here. I measured the shoulder length and then fire formed in my rifle. I got the reading and bumped .002 back. Now I am on the 4 the firing and happened to check the measurement and its now .004 longer than the initial once fired readings I have. Anyone else experience this with their brass? Note I use AMP annealer after every firing also.

I think the original, once fired measurement is largely irrelevant as long as it chambered, right? You want to compare to the 2nd firing measurement after fire forming in your chamber. Or am I missing something?

 

[menhaden_man]

I use Peterson brass for my 7RM and noticed the same thing. Pretty sure it's not done 'stretching' for the first few firings. Check them out online, they are (or were) selling 7RM 'long' brass to help minimize this.

 

[menhaden_man]

Peterson Brass 7mm Remington Mag Long Unprimed Box of 50 - Graf & Sons

All 50 count listings of Peterson Cartridge casings come in one of their plastic ammo boxes. Made in the U.S.A. Peterson Cartridge Co is committed to producing Match-Grade Brass that enables our customers to get more reloads per casing than industry average. Warning: Only use Peterson...

www.grafs.com

 

[BossGobbler2024]

I think the original, once fired measurement is largely irrelevant as long as it chambered, right? You want to compare to the 2nd firing measurement after fire forming in your chamber. Or am I missing something?

That is what I did. If my wording made it sound like it wasn't, my bad. I used the fire formed measurement from my gun to base my loads off of. I didn't think that twice fired brass would move much more but apparently it does, at least for this gun.

 

[BossGobbler2024]

I use Peterson brass for my 7RM and noticed the same thing. Pretty sure it's not done 'stretching' for the first few firings. Check them out online, they are (or were) selling 7RM 'long' brass to help minimize this.

Thanks for the reply. The brass I purchased was from once fired Gunwerks reportedly from the member here. I was all in good condition and all measurements were consistent for them before I started shooting them to form to my chamber.... trim and shoulder.

 

[BossGobbler2024]

I guess I either bump the brass to the "new" length or continue with what I have been using. I will at least test the "old" vs "new" length to see if any velocity or impact difference is significant.

 

[SDHNTR]

Not sure I understand your post. You were expecting once fired brass in some other barrel to have same or very similar dimensions to fired brass in your barrel? Thats a big assumption, too big.

Sometimes brass even when only shot in one barrel needs a couple/few firings to fully fireform to the chamber. Depends on the chamber cut dimensions vs the brass dimensions.

This is especially common with belted mags that headspace off the belt. There’s a figurative mile of space in front of the shoulder on most belted mag chambers. I generally just neck size for the first 3 firings before I even begin to start measuring.

 

[SDHNTR]

I use Peterson brass for my 7RM and noticed the same thing. Pretty sure it's not done 'stretching' for the first few firings. Check them out online, they are (or were) selling 7RM 'long' brass to help minimize this.

Yes, because of what I posted above about how a belted mag headspaces.

 

[BossGobbler2024]

Not sure I understand your post. You were expecting once fired brass in some other barrel to have same or very similar dimensions to fired brass in your barrel? Thats a big assumption, too big.

Sometimes brass even when only shot in one barrel needs a couple/few firings to fully fireform to the chamber. Depends on the chamber cut dimensions vs the brass dimensions.

This is especially common with belted mags that headspace off the belt. There’s a figurative mile of space in front of the shoulder on most belted mag chambers. I generally just neck size for the first 3 firings before I even begin to start measuring.

I was not expecting the brass from another chamber to have similar readings. I was expecting that after 4 firings the the brass would not be .004 different from the first firing in my rifle (which is actually the 2nd firing on the brass). Not a huge deal, just curious if others had experienced the same.

 

[SDHNTR]

I was not expecting the brass from another chamber to have similar readings. I was expecting that after 4 firings the the brass would not be .004 different from the first firing in my rifle (which is actually the 2nd firing on the brass). Not a huge deal, just curious if others had experienced the same.

Not uncommon. Your rifle’s chamber might just have a bit more space vs the brass’ original dimensions.

 

[wind gypsy]

Yes, not uncommon for it to take multiple firings until a shoulder is maxed out with it's forward movement. That's why people can get away with just neck sizing for a few firings before having to bump shoulders in many cases.

 

[wapitibob]

I was thinking of switching at some point to7prc but I’m curious how much stretch are you seeing total from virgin Peterson brass till fully formed in a saami chamber?

 

[Don Fischer]

When I shot the 7mm Rem Mag I had trouble with splitting the case head. Found out a problem with magnum case's is they headspace on the belt, not the shoulder. Could be your cases are made to spec but the rifle has a sloppy chamber. At .004" do you feel the shoulder rubbing when you close the bolt or can you not even close the bolt. I never had a problem with bolt closing when I was splitting heads. The fix was easy, partial size. secnd firing don't FL size just down the neck far enough to hold a bullet in. Couple times like that and you will either feel the shoulder drag or simply not be able to close the bolt anymore on the neck sized case. Problem is the case grew to fill a sloppy chamber. Now partial size. Fron where you were neck sizing screw the die in a bit more and pay attention to the die mark on the neck. Once it reaches the neck shoulder junction go down about a quarter turn at a time and check after every run through the sizing die to see if the case will chamber with no rubbing of the neck. Once your there, lock the die in and keep it locked in. At that point the die resizes the case to fit that chamber. I use that method anymore for sizing all my cases, even non belted cases. Every one of my rifles has it's own sizing die. Had a couple 243 that demonstrated it pretty well. Both had their own set of dies and neither rubbed the neck at all chambering. But the case's would not fit in both rifles from one of the dies. One rifle had a bit larger chamber. If you size to the sammi spec., the case will always fit any rifle with a sammi spec chamber. Keep in mind that when chamber's are reamed, there's a min and max size

 

[swavescatter]

What’s all this belt talk???

 

[BossGobbler2024]

I was thinking of switching at some point to7prc but I’m curious how much stretch are you seeing total from virgin Peterson brass till fully formed in a saami chamber?

I can't speak to virgin brass as I have started with once fired brass from Gunwerks. I can speak to the changes I have seen. With my comparator the shoulder on the once fired brass from Gunwerks was 48.10mm and now after multiple firings I get a fired measurement from my gun chamber of 48.18 mostly with some 48.19 and a few even 48.20mm. After the initial fire forming of brass to my chamber I got 48.14mm on almost all rounds from my gun.

 

[wapitibob]

I can't speak to virgin brass as I have started with once fired brass from Gunwerks. I can speak to the changes I have seen. With my comparator the shoulder on the once fired brass from Gunwerks was 48.10mm and now after multiple firings I get a fired measurement from my gun chamber of 48.18 mostly with some 48.19 and a few even 48.20mm. After the initial fire forming of brass to my chamber I got 48.14mm on almost all rounds from my gun.

appreciate it, thank you