Working up a load for a friends 270 win Remington pump gun. Had cratered primers on beginning loads. (least amount of recommended powder)velocities were correct according to the manual. Stopped there, shot some factory rounds of different manufacture and bullet weights and had the same result. Should I worry? what could cause this? Look just like the photos in the manuals that say signs of too much pressure. Thanks in advance

If the primers are flattened as well,then yes it's a pressure problem.
Cratered primers can be caused by a rebounding firing pin or an oversized firing pin hole.

quote:

Originally posted by Rapidrob:
If the primers are flattened as well,then yes it's a pressure problem.
Cratered primers can be caused by a rebounding firing pin or an oversized firing pin hole.

10-4 roger

Thank you, no flat primers. Incidentally, this looks to be very accurate pump gun with the factory ammo! What causes rebounding firing pin, and is that something that should be addressed?

I would suspect your pump gun, if it is a Remington, has a slight headspace issue causing the case to move in the chamber. All of mine did.

Measure the new cases versus the fired cases to be sure. From there, it is a matter of just sizing the case just enough to fit the chamber reliably again.

eny
Many causes for a given problem, one of the main reasons for working up from the bottom is that a sudden change is indicative of a problem.
IE: If the primers had no sign of a crater until you reached the upper end of the charge range, that would be a reason to stop/back off.
As yours are doing it at starting levels, and with factory loads, it's a gun issue not a loading issue.

Second question, as the primers you're using came out of the factory in a FLAT state, just how are you going to judge "flattening"? Back in the old days, they used to sell convex shaped primers, as well as flat primers, on those (convex) you could judge some amount of flattening of the dome.

FYI, below (L-R) factory, book max and overloaded primers

Unless you are actually blowing primers, or making them leak, then ignore what they look like. Soft ones react differently. I have been reloading for 50 years and I do not know what a "cratered" primer is or means. Soft primers will crater with a starting load. Bolts with large firing pin holes will show some primer material extruding into them; means nothing. Hard primers will leak before they crater; so that term pretty much is meaningless.

I've been loading for over 60 years and I understand what the term " cratered " primer means to all but a few. It may not be totally precise but the message comes through clearly.

roger

The firing pin channel or hole may be a little larger in diameter, then normal.
This will let the primer flow back into the hole around the firing pin.

With factory and reloads doing it, i dont see a problem.

Reload left, factory on right. Rem 700.

Do this, take a magnifying glass and look closely at the firing pin hole.
Remington went through a few years where they put a bevel of 45 degrees on the hole, this is what causes the crater.
I have the same problem, when I get around to it, I will bush it to fix the problem.

Cratered primers are no problem, they will give a slight resistance to opening the bolt, however.

Cheers.

Ok.........Time to re-post something from 2014

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Cratering occurs when the firing pin is forced, by pressure, slightly to the rear.....exposing the boltface hole bore by the pin's hemispherical tip, creating a gap. This gap is then filled by primer cup metal.....making a primer crater. Too much movement, of the firing pin tip, rearward.....and the primer blanks.

As a reference, and a good read, refer to Precision Shooting magazine, May 2001, page 31, "The Real Reason Primers Pierce" by Jerry Stiller.

Hope this helps.

Kevin

Thanks guys, will get a closer look at the rifle tomorrow.

There is no message in cratered primers; too many things cause it and excess pressure is not necessarily the cause.
If our loads are not causing primers to leak and your pockets remain tight, then ignore cratered primers.

X2

Photo is from said Remington. Factory
will repair free, if returned, last i heard?

A weak firing pin spring will let primers flow more. (as all ready said)

quote:

Originally posted by 416RigbyHunter:
Do this, take a magnifying glass and look closely at the firing pin hole.
Remington went through a few years where they put a bevel of 45 degrees on the hole, this is what causes the crater.
I have the same problem, when I get around to it, I will bush it to fix the problem.

Cratered primers are no problem, they will give a slight resistance to opening the bolt, however.

Cheers.

my sons Mossberg ATR 30-06 does this with all ammo as well.

I have had 3 misfires recently so maybe I need a new firing pin from what I am reading here.

A cratered primer means nothing to me unless it has a black ring around it that indicates pressure..A flat primer with a extractor mark on the case or a sticky bolt is pressure and time to cut back a grain or even two..a flat primer that falls from the case when reloading is caused by pressure..

This primer business as an indicator has been around so damn long a passed around in magazines and loading books that its become the rule of law in some circles..Its pure bunk..To me its nothing more than to remind be to be looking for other pressure signs.

Cratered primers are a too lage firing pin whole and that should be fixed in a few cases. but ignored in most cases..It can be a tad of head space and its found in a lot of old Winchester lever actions, in fact most..In a bolt gun proper handloading can cure headspace.

The photos posted above by 2 members are perfect.

The first post with the lower photo shows the "hat brim" on the right primer indicating unsafe load.

The second post 204 Ruger pics show primer flowing back into a large firing pin hole.

BTW Pump & Semi auto actions have loser tolerances. The recoil of the rifle will back the primer out a tiny bit and then slam it back in against the bolt face. This is normal in ALL rifles. It is the law of physics.

Try neck or partial FL sizing the cases to fit that particular rifle chamber headspace and then see if you get the same issues with primers. I suspect that you will not repeat the same unless the firing pin hole is large.

If this is an old 760 pump, there is no spring retaining that firing pin. At least there is none in mine.