338 Lapua brass oddness??

[JustBC]

I have been reloading for a few years now but I tried my first loads for 338LM today. I saw something I've never seen before.

There is a visible shiny stripe down by the case head. See photo. There were absolutely no pressure signs, no sticky bolt, no primer cratering, no flattening etc.

I am well within the limits for Retumbo with a 300 grain Berger, (91.5 grains with CCI Magnum primers). The brass is Lapua, never sized, first firing. I stopped shooting immediately when I saw the mark on the brass.

When I got home I looked at some once fired brass from factory ammo (IMI, Barnes and S&B) and saw the same type of shiny stripe.

I measured the the case depth on all the different brass. The shiny stripes line up almost exactly with the case web.

As near as I can tell when the brass expands it knocks the shine off a bit. Where it can't expand because of the web it keeps the shine.

Since I am new to 338LM reloading I am a little paranoid. Has anyone seen something similar?

FWIW the rifle is a Sako M10.
Thanks.

 

[Supersubes]

Have you taken any headspace measurements between virgin brass and fired brass? Virgin lapua brass is much shorter than spec lapua chambers. Could be stretching, could just be the the lowest point on the case that expanded out to meet the chamber. Looks much further up the case than is normal though.

 

[JustBC]

Not yet but good idea... The thing is, there were identical marks on brass from factory ammo. It is not just Lapua brass.

 

[Supersubes]

Probably chamber related then.

 

[whatsupdoc]

I have been reloading for a few years now but I tried my first loads for 338LM today. I saw something I've never seen before.

There is a visible shiny stripe down by the case head. See photo. There were absolutely no pressure signs, no sticky bolt, no primer cratering, no flattening etc.

I am well within the limits for Retumbo with a 300 grain Berger, (91.5 grains with CCI Magnum primers). The brass is Lapua, never sized, first firing. I stopped shooting immediately when I saw the mark on the brass.

When I got home I looked at some once fired brass from factory ammo (IMI, Barnes and S&B) and saw the same type of shiny stripe.

I measured the the case depth on all the different brass. The shiny stripes line up almost exactly with the case web.

As near as I can tell when the brass expands it knocks the shine off a bit. Where it can't expand because of the web it keeps the shine.

Since I am new to 338LM reloading I am a little paranoid. Has anyone seen something similar?

FWIW the rifle is a Sako M10.
Thanks.

View attachment 6864725


If you are describing the line that circles the case around 3/8 from the base, that looks like the unsupported section of the cartridge.

Between where the bolt ends and where the the chamber begins the brass is unsupported making that ring.

Remove the bolt an place the case in the bolt head does the line match the end of the bolt?

Normal

 

[JustBC]

Missed this reply.. I will take a look tomorrow.

 

[Fursniper]

Exactly the same mark on my fired brass too.

 

[JustBC]

@Fursniper Thanks, that is reassuring. @whatsupdoc I checked the mark does not line up with the end of the bolt at all. I am pretty convinced at this point that my original hypothesis about the case web preventing expansion is correct. Since Fursniper has the same type of marks I am going to stop worrying about it. Thanks guys!

 

[GIXXER2000]

I also have the same marks on my brass. In my AI I got the best accuracy with 90.5 Retumbo with the 300 Berger's.

 

[Juggerxxx]

Just got done firing my first fifty handloads and resizing them and thought of you and this thread.
As you can see my Lapua Brass looks the same way. All fifty that have been fired once and resized. The line showed up right after resizing.
Shot in a desert tech SRS and the sizing die is a Redding S type.

 

[JustBC]

Thanks Juggerxxx

 

[JustBC]

Have you taken any headspace measurements between virgin brass and fired brass? Virgin lapua brass is much shorter than spec lapua chambers. Could be stretching, could just be the the lowest point on the case that expanded out to meet the chamber. Looks much further up the case than is normal though.

Boy you were right about it being shorter. I measure about .006 short. Interesting they do this.

 

[MrSmith]

When shooting a case for the first time it is advisable to make sure all of the "stretch" happens in the annealed portion (the upper body, shoulder and neck) of the brass. In this area the, say, .006" stretch is distributed over 1/2" or so of length. If this stretch is allowed to happen at the rear of the case the unsupported portion of the case that doesn't include the case web is very short, less than 1/8". The same .006" distributed over this shorter distance will result in thinning of the brass and create a weakened zone. It may not be enough to ruin the case but a weak section has been created and resizing will not remove it.

When triggered, the ejector is holding the brass some distance forward of the boltface. The primer and powder burns, pressure builds, and the case obturates to seal the chamber. The body of the case is now solid to the chamber walls. Any gap at the shoulder is fireformed forward to the chamber in the annealed portion. Any gap at the rear is fireformed rearward to the boltface in the unannealed portion. This rearward stretch will damage brass.

When I fire a virgin case I will squeeze the shoulder (vise or pliers) very slightly so as to barely oval the lower shoulder. As the round is chambered the bolt must force the case into the chamber. This drag should be enough to overide the ejector and force the brass aginst the boltface. When it fires all of the stretch goes forward and the case is fireformed to that chamber. By resizing only enough to allow chambering this only needs done once.

How your reloading dies are adjusted to set the shoulder back on the fired case is personal preference and rifle specific. For target loading I prefer to barely move the shoulder back and then only when chambering becomes unacceptably tight.

Thank you,
MrSmith

 

[JustBC]

That makes a lot of sense. Thank you Mr Smith.