Cratering primers

[Hetzer]

My 6.5x47 load that I have used for the last two seasons has started cratering the primers. Pierced a couple during testing. It's been trouble free to this point. Same jug of N150, same batch of Rem 7 1/2's, same box of Berger 140 Hybrids. (yes, I need to shoot more) It's not a real hot load. 36 gr of N150 and the COAl is 3.100. Yields about 2680 fps.

So I'm thinking this means my primer pockets are starting to loosen up. Does this sound about right? It's the only thing I can think of that sounds half way plausible.

 

[Supersubes]

Show us some pics.


Loose pockets should have nothing at all to do with it. Piercing a primer causes hot and high pressure glasses to erode the firing pin and it’s orifice, which tends to worsen any existing situation (More cratering or more piercing). What came first, the cratering, or the piercing(sounds like the piercing)?

Loose pockets can cause leakage from around the primer as well, which will erode a ring in the bolt face. Neither is a good situation, and should be corrected.

 

[Hetzer]

Here's what I'm getting.

 

[Conaso]

Whoa, that's cratering!

 

[Hetzer]

That's on the more extreme end of the spectrum. Some are way less amd not at all.
I also checked the scale. Using an A&D 120 (?) and weighed to the .02 to .04 gr. About one to two kernels.

 

[wvlapua]

Get some CCI 450 or BR4 primers. They have a harder cup.

 

[Deleted member 10043]

Two things to check is the firing pin is not getting stuck when the primer ignites the case and throat obstruction like carbon. Also, check the face of the bolt.

 

[lash]

^^^I agree to check for these conditions before making changes to your load.^^^

 

[MtnCreek]

^ agree on some type of obstruction in the neck area.

See if a bullet slides freely into a fired, unsized case.

I would not shoot that any more until corrected.

 

[powerspc]

Can it be a worn firing pin or worn breechblock? Cratering is usually 1) Over pressure or 2) A loose fit between the firing pin and the opening in the breechface. If it's the second case then your factory rounds should show some cratering as well, if they don't then I would guess over pressure.

 

[Deleted member 10043]

Over pressure is just a symptom of the problem based on the information provided.

 

[MtnCreek]

The case with the primer flow shows an ejector swipe mark as well.

 

[wvlapua]

Make sure you have adequate bullet release. If a bullet will drop into a fired case you are good.

Make sure your chamber is dry and free solvents, oils and other contaminates also.

If all checks out. CCI 450 or BR4. The brass shown doesn't appear overpressure. Primers still look round to me.

 

[Steel head]

That’s some impressive cratering!

 

[Greg Langelius *]

I am inclined to think pressure, based on the sharp primer edges in evidence in the pictures.

My suspicion is that there's some sort of a pressure ring built up in the throat/near end of the bore, contributing to a pressure spike.

Perhaps a vigorous cleaning process in the chamber end of the bore? Verify that the bullet isn't jamming in the rifling, too.

Greg

 

[Steel head]

I am inclined to think pressure, based on the sharp primer edges in evidence in the pictures.

My suspicion is that there's some sort of a pressure ring built up in the throat/near end of the bore, contributing to a pressure spike.

Perhaps a vigorous cleaning process in the chamber end of the bore? Verify that the bullet isn't jamming in the rifling, too.

Greg

This!

 

[MtnCreek]

Also look for necks too long and the possibility of a donut in the necks.

 

[Hetzer]

Thanks for the ideas Gentlemen. It's been sidelined for now till I get more time to look it over.
I'll update more after that.

 

[MarinePMI]

Another possibility is residual case lube on the cases in conjunction with a shoulder that has been pushed back a bit too far. This would allow the case to move forward under firing pin impact, and then slam back against the bolt face upon ignition. This happening would expose a firing pin being on the hairy edge of too long, and would pierce primers and cause cratering.

Just a thought...