Thread: Brass life...

Hey team I've been exclusively using Peterson SRP 6CM brass in my match rifle.

I have started to notice its getting sticky extraction in its last few firings. Zero pressure signs

Currently at 14 firings and the pockets are still tight as.

Have annealed them but doesn't seem to change it.

Is it a case of they have reached the end of their life and the case head area just isn't acting as it should?

Cheers for your input

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Greetings @Ben-welder,
Some information on your case sizing process would be helpful. It seems that your tight pockets should rule out any case head expansion and your 14 loads would indicate that you are not oversizing them so the question is how are they being sized?
Grandpamac.

Originally Posted by grandpamac

Greetings @Ben-welder,
Some information on your case sizing process would be helpful. It seems that your tight pockets should rule out any case head expansion and your 14 loads would indicate that you are not oversizing them so the question is how are they being sized?
Grandpamac.

Cheers for the reply. I full lenght/ shoulder bump 2thou each time. I'll measure what the case head expansion is on a fired s sized case shortly.



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Cleaned the bolt and chamber recently?

I've had tikkas get a bit of dirt in the wrong place and almost need a mallet to open.

Originally Posted by Ben_welder

Cheers for the reply. I full lenght/ shoulder bump 2thou each time. I'll measure what the case head expansion is on a fired s sized case shortly.



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That should give easy chambering and there are no rub marks on the case bodies so I think I am with Pommy that a good bolt and chamber clean with some moly lubricant on the cocking cam surfaces will likely sort things out.
Grandpamac.

If when you lift the bolt it is tight all the way the issue is an over length problem, but it sounds like you have good control of your lengths sizing ie 2 thou bump.
If when you lift the bolt it is relatively easy up to the point when you reach the primary extraction cam and then there is a "click" this is a sign of a tight base.

Unfortunately, some dies just won't size that last bit above the base sufficiently once it has expanded over many firings.
I have found this with the 308 and had to borrow a mate's small base die. I think small base dies may only be made in 6mm BR and 308.

If you have some new brass measure above the base and compare with your 14x cases.

I recently posted a link to Alex Wheelers "click" test video for expanded and tight base brass.

How do you determine your 2 thou bump?

Originally Posted by zimmer

If when you lift the bolt it is tight all the way the issue is an over length problem, but it sounds like you have good control of your lengths sizing ie 2 thou bump.
If when you lift the bolt it is relatively easy up to the point when you reach the primary extraction cam and then there is a "click" this is a sign of a tight base.

Unfortunately, some dies just won't size that last bit above the base sufficiently once it has expanded over many firings.
I have found this with the 308 and had to borrow a mate's small base die. I think small base dies may only be made in 6mm BR and 308.

If you have some new brass measure above the base and compare with your 14x cases.

I recently posted a link to Alex Wheelers "click" test video for expanded and tight base brass.

How do you determine your 2 thou bump?

Bolt lift is fine it's when pulling the bolt back. My new batch of brass has 2 firings on it with zero issues. Both are Bumped to the same dimension.

The strange thing case head on the newer batch measures the same as the old batch both in fired and sized form.

I did just measure my case length on my old batch and they are over lenghg but this wouldn't give extraction issues?

Shoulder bump is measured with a bushing a machined to sit just inside the shoulder radius. Gives me a datum to measure from.


I'm not too stressed about throwing the old batch would be cool to know where the issue is coming from

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Its telling you its time to rebarrel a 7mm creedmoor .

Originally Posted by Ben_welder

Bolt lift is fine it's when pulling the bolt back. My new batch of brass has 2 firings on it with zero issues. Both are Bumped to the same dimension.


I did just measure my case length on my old batch and they are over lenghg but this wouldn't give extraction issues?


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Try the black marker pen method to determine where the tight spot are.
Four stripes spaced around the case, top to bottom.

When you say overlength, by how much? This can create another more serious issue ie projectile pinch and very high initial pressure.

About 10thou over max case lenght. The chamber fine and show no issues pressure wise but the extraction is average. I'll mark on up tonight and chamber it. Even trying to re chamber a fire case is tight

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Originally Posted by lau lau

Its telling you its time to rebarrel a 7mm creedmoor .

Filthy man you are haha

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Listen to @zimmer....he and I have encountered this with a multitude of calibres. The differences in base size is very little....a case can jam if it's 0.0001" over size and I would be very surprised if you can consistently measure that.

Some factory dies simply do not reduce the base enough and it is worth preserving that brass now it has reached optimum hardness.....get a small base die or that of another manufacturer like Forster which seem to be tighter on some calibres.

Have your ever trimmed these cases? What is the length of an unloaded case?

I use Lapua Palma cases. Full length size after every firing.
When I got to the 15th load some started to be harder to get the bolt to close.
When I measured the fired case they were 2.030 - 2.035, the spec is max 2.015. Time for a trim.
Trim back to 2.010 problem resolved.

Ive heard some really good things about this Peterson brass. 14 firings is going well. But I hear what your saying about finding the issue.

Heres a link to what Ive read about Peterson V Lapua in .338 sorry pics wont load for me but it may be of interest.
https://www.snipershide.com/shooting...38-lm.6401381/

Being from Oamaru I suspect your not fully engaging your 6th finger on the bolt handle and its harder than it used to be...