Cratering and slightly flattened primers with factory ammo

[toaster]

First of all, as this is my first post I'd like to say hi and thankyou for all the info I've already picked up from this great forum!

I live in England and I'm a relative newcomer to centerfire rifles although I've been shooting shotguns and rimfire for quite a few years - recently I picked up a pre accutrigger Savage 111 in 25-06 to use as a deer rifle.

Having shot just a handfull of factory rounds I seem to be getting some cratering and also some flattening of the primer:

[img width=600 height=450]http://i366.photobucket.com/albums/oo104/shaggyDogsPhotos/primers.jpg[/img]

The ones on the left are Prvi Parizan (unfired and fired) and the ones on the right are Sako (fired and unfired)

Before shooting the bore was cleaned removing a lot of copper and carbon fouling - I made sure there was no oil, solvent or any other crud in the barrel or chamber.

I'd be really grateful for people's opinions and please let me know if there's any more info I can supply.

All the best

Martin ;D

[BillPa]

Hey Martin...Welcome!

Cratering is more a visual annoyance than anything else. If they were blanking (perforating), well, that would be a problem.

If you want to fix it, take a close look at the firing pin tip. From the factory you see they're ground on somewhat of a taper. Since when firing a round the primer stops the pin forward travel at about .020" protrusion the taper allows a bit of a gap between the pin and the pin hole for the primer cup to enter...craters!

By reshaping the tip to a radius, about .020" is good, the full diameter of the pin remains in the hole and eliminates 90% of cratering problems as long as they're caused by other problems, over loading and etc.

You may also find a bit of a chamfer on the edge of the in hole in the bolt face. That can also contribute to some cratering, but requires taking a facing cut across the bolt face or a more radical approach, rebushing the pin hole. For now I'd reshape the pin tip and go from there.


Bill

[toaster]

Thanks Bill

I see what you mean about the taper on the pin - if the pin is being stopped with just a .020 protrusion then it's definitely going to be a loose fit in the hole. I had thought about replacing the bolt head as there's some very slight pitting on the face - again, more of an annoyance than anything else but it might make sense to give the bolt a complete overhaul and tune-up.

As for the flattening of the primers would you think that's anything to worry about?

[358Hammer]

Welcome Martin

Think BillPa took care of it.

Neal

[BillPa]

Thanks Bill

I see what you mean about the taper on the pin - if the pin is being stopped with just a .020 protrusion then it's definitely going to be a loose fit in the hole. I had thought about replacing the bolt head as there's some very slight pitting on the face - again, more of an annoyance than anything else but it might make sense to give the bolt a complete overhaul and tune-up.

As for the flattening of the primers would you think that's anything to worry about?

Cratering and flattened primers in some ways are or can be caused two different things. Looking at your pictures the primers don't appear to be flattened, just some cratering, the edges are still rounded. If it would be result of a pressure problem I would guess the edges would be flat, almost square and I'm not seeing that, they look completely normal in that respect. I'll also make the assumption fired rounds extracted normally. If the primer were flattened and the extraction sticky I'd be looking at other things, but as I said, I not seeing any indication of pressure.

Chances are better than even reshaping the tip alone will completely eliminate or reduce the amount of cratering. I'd attack the bolt face second.

Bill

[RoscoeT]

I had the same problem.

The smith reamed my chamber to the upper end of the sammi spec and it went away.

Hope that helps.

[toaster]

I'll also make the assumption fired rounds extracted normally. If the primer were flattened and the extraction sticky I'd be looking at other things, but as I said, I not seeing any indication of pressure.

Nope, the bolt lift was as normal and no extra force was required to eject the case


Btw - thanks mods for moving this thread to the right section ::)

[BillPa]

Here Martin, I took some of my infamous rotten pictures. Even with a new camera I can screw them up! ;D

Here are two pins, the left original, the right, with the tip reshaped.


Here I adjusted both pins for .020" protrusion using the same bolt head, the average amount a primer would be indented when struck.

Original with .020" protrusion.


Reshaped


Hopefully you can see the gap between the original pin and pin hole, more than enough room for the primer cup material to flow into causing cratering without any other obvious signs of pressure, extraction,flattened cups and etc.

Bill

[Eric in NC]

I had the same problem.

The smith reamed my chamber to the upper end of the sammi spec and it went away.

Hope that helps.

Increasing headspace would tend to make that problem worse.

[toaster]

Thanks for posting the pics Bill - not rotten at all ;D they illustrate very clearly what needs to be done.

I had wondered if this might've been caused by slightly too much headspace - as the rifle has seen a bit of action I thought the lugs may have worn enough to give the bolt-head a little freedom, but checking with go-no-go gauges shows everything is as it should be.

[markr]

I had the same problem.

The smith reamed my chamber to the upper end of the sammi spec and it went away.

Hope that helps.

Increasing headspace would tend to make that problem worse.

I was just about to post about having the headspace checked...but I won't do it now! ;D
As well as not saying anything about headspace, I won't mention that in my experience with the 222 family of cartridges, a CCI magnum primer or a Remington 7 1/2 has either lessend this problem or made it go away.

[dcloco]

....or....oversizing cases will cause this problem also.