Primer Cratering??

[Muelsy]

I am getting primer cratering in my hand loads and am not sure why. What does this mean? I have tried WSM and CCI 450 primers and both are cratering. I have about 200 rounds through a Rem 700 SPS. I am loading H335 & H322, 32 & 40grn V-Max's with Winchester brass. Never loaded anything above max. I did shoot 2 boxes of factory Rem ammo when I first got the gun and didn't notice anything with the factories??

[Joe O]

If you still have any of that factory Remy brass,take a look,otherwise try Remy primers and see if you still get the cratering.Seems comonplace for new guns to have craters in all ammo,due to a poor fit of the firing pin and/or protrusion.My Savage was so bad,it was hard for me to believe it ever left the factory.My new Remy bolt has minor cratering.If I could post a pic,I'd show you both.Call customer service and see what they say.Never mention reloads regardless if they are lower pressure than factory.If the factory won't help you out,you can eithe,buy an aftermarket bolt,or,my choice,send it off to Gen-Tan and have the fireing pin bushed.About $85 inc shipping back in three days.





http://gretanrifles.com/

[Fred_C_Dobbs]

There's cratering and then there's excessive cratering.

Cratering happens because high pressure causes the primer cup to flow around the firing pin and into the hole between it and the bolt face. This can happen for any or all of three reasons. First is an excessively large firing pin hole hole, which leaves a gap around the edge of the firing pin itself. Second is a weak firing pin spring. Third is excessive chamber pressure.

The key to reading excessive pressure signs is increasing the charge weight gradually, examining each case after firing (I use a 6x hand lens) and looking for the onset of each "sign." You really have to get to know the individual rifle, as well as your bullet components. Like Joe, I have a .204 Savage that craters with relatively low pressure rounds, even with factory Hornady loads. And some primers have a reputation for being either "hard" or "soft." Soft primers are the ones that will show cratering at lower pressures.

Besides cratering, you need to also look at primer flattening. Most primers have less rounded shoulders now than they used to, but even the new ones will get flatter, with more squared shoulders as the pressure rises.

Pressure gets higher as you move left to right:



Notice how the appearance of the ring between the primer and the rim gets narrower and shallower as you move right, indicating the top of the primer is getting wider (and flatter). This is consistent with increasing chamber pressure. Notice, too, there is no cratering in the leftmost round. Second leftmost, slight cratering. At furthest right, the cratering mysteriously has vanished because it smacked the bolt face so hard, it was smushed back into the primer. I suspect this primer also is "top hatted," meaning it now is wider at the top than at the bottom, like a top hat.

This is a slightly top-hatted primer:



IMHO, top hatting always is a symptom of excessive pressure.*

Cratering itself might not be conclusive but excessive cratering is a prelude to primer piercing. And it is possible to get pierced primers before you get pronounced flattening (usually because there's something amiss with your firing pin).

It's also possible to get blown primers, which literally will fall out of the brass when extracted. Or in less severe cases, the primer pockets could just get looser the first few times they're shot, which you'll notice because it takes less pressure to seat the new primer.

*But all these primer problems also can be caused (or contributed to) by excessive headspace.

If you've approached it cautiously and loaded incrementally hotter loads, you can tell a lot from the change in the force required to lift the bolt handle with subsequent loads. Under such high pressure, the rim of the case also will flow into any available depression, like the cut-out for the ejector. Once the rim has begun flowing into the ejector, the case will begin to bind against the bolt face, increasing the effort needed to turn and open the bolt. A little bit of extra bolt lift effort isn't necessarily a bad thing but that's a decision you and your rifle need to make together. If you have to use a rubber mallet to open the bolt, ...that's probably a little excessive.

This "flowing" also will leave a distinctive mark on the casing, known as ejector smear (or swipe):



This one was fired in a semiauto. The smear in bolt actions usually is shaped like a hemisphere or a tombstone. Soft-ish brass can show ejector smear before you've reached the point of stiff bolt lift.

The bottom line is nothing can beat the experience you'll gain by loading incrementally hotter, approaching a max load slowly, and learning the order and at what point the pressure signs appear in your particular rifle. And just because you've reached the onset of a single sign of excessive pressure, that doesn't necessarily mean your load is unsafe.

The picture of the smear mark is a good example. That primer is still severely rounded, which would lead me to speculate that this brass is soft-ish, because the primer shows no hint of cratering and very little if any flattening.

Some people use case head (or webbing) expansion as an indicator of excessive pressure. But it's unsettled whether this really is a reliable indicator, plus it requires being able to accurately measure to the ten-thousandth of an inch. But it is a quick and dirty test of webbing expansion to try to fit the just-fired case into a case holder. If it won't fit, that's a pretty good indicator the case webbing has expanded too much.

A chronograph also is a great tool for double-checking your pressure observations.

[Fred_C_Dobbs]

I shot this this weekend:



It's Federal match brass, which is famously soft. And bolt lift effort was normal so the extractor smear does not concern me. In fact, also you can see the smear from three previous firings. The primer shows light cratering and slight flattening (but you have to compare to an unfired case to judge the flattening).

So this cartridge shows three pressure "signs" but none of them is "excessive."

If the bolt lift had been stiff, or if this had been Winchester brass (which is not known to be soft), I'd have been double-checking my load figures.

[Silverfox]

This post should be pinned, IMHO.

Fred_C_Dobbs--Excellent write-up and photos.

When I have a factory bolt rifle and I the primers show signs of the flow of primer metal around and into the area of the firing pin hole, that bolt gets a quick trip down to Gregg Tannel for a firing pin hole bushing job. Gregg has done two Remington 700 bolts for me and I also had him bush a Savage 12VLP in .204 Ruger bolt for me this spring. He does excellent work, very quick turn-around time and although his price has gone up over the years, it is still very reasonable (don't tell him I said that).

[Jim White]

This post should be pinned, IMHO.

Fred_C_Dobbs--Excellent write-up and photos.

When I have a factory bolt rifle and I the primers show signs of the flow of primer metal around and into the area of the firing pin hole, that bolt gets a quick trip down to Gregg Tannel for a firing pin hole bushing job. Gregg has done two Remington 700 bolts for me and I also had him bush a Savage 12VLP in .204 Ruger bolt for me this spring. He does excellent work, very quick turn-around time and although his price has gone up over the years, it is still very reasonable (don't tell him I said that).

Agreed...

[jo191145]

I agree also. Fred did a great job of explaining/perhaps disuading fear of pressure signs.

I've seen a handful of loads that shoot well at moderate pressures. I've seen more that run at the edge.
I've seen a whole lot more that shoot terrible at very high pressures.
Its good to be able to discern just how high you can go.

[Sam in Perth]

I'm not sure what "pinned" means, but that is the first time this whole issue has made sense to me.

Thanks Fred.

[Jim White]

Sam,

Pinned means that it stays at the top of the "topic list" (just the like the "Disclaimer & Favorite Loads") as opposed to being shown by the last activity date. It just makes it easier to fine.

HTH,

[Sidewinderwa]

Fred, you did an excellent job, especially with the pictures. Best I have seen. I agree, this should be pinned.