What causes primer cratering?

[ARCHIVED THREAD] - What causes primer cratering?

Posted: 11/6/2010 6:28:50 AM EDT

I picked up a spent hull after I shot a deer the other day. Today I was just fondling it while I was driving my truck. I noticed that where the primer indentation is that there is a raised circular lip...basically primer cratering.

I was not shooting handloads. I was using factory ammo. I was also using a Mosin Nagant. IIRC there is a screw at the back of the bolt on a M/N and you can set your firing pin depth. Maybe I have it set too high?

Posted: 11/6/2010 6:30:20 AM EDT

[#1]

I had a SAR 3 that did this... was told my issue was caused by headspace.

Posted: 11/6/2010 6:34:03 AM EDT

[#2]

Everything I have ever been told by many years is that it is caused by higher than normal pressures.
Might be thin metal in the primers.
Isn't neccesarily dangerous levels, but it is high pressure.
The primer is being pushed back into the firing pin hole.
OP knew this, it's why he said he isn't using reloads.
Mass produced ammo will have deviations in the powder loads.

Posted: 11/6/2010 6:34:09 AM EDT

[#3]

Weak firing pin spring, or excessive pressure.

I belive what happens is that the firing pin is pushed back after ignition by the primer bulgeing ourward, and then the pin returns under spring pressure but cannot fully invert the bulge (this forms the crater appearance).

Posted: 11/6/2010 6:35:25 AM EDT

[#4]

Hulls are spent shotgun shells. I'm guessing you have a MN 7.62 x 54R brass shell. Cratering is usually overcharge, but like you mentioned, the pin could be striking a little deep. Did you get one of those screw driver / pin gauge tools with your MN?

Posted: 11/6/2010 6:38:09 AM EDT

[#5]

Quoted:

Hulls are spent shotgun shells. I'm guessing you have a MN 7.62 x 54R brass shell. Cratering is usually overcharge, but like you mentioned, the pin could be striking a little deep. Did you get one of those screw driver / pin gauge tools with your MN?

sorry about the nomenclature. Yes, I have one of those said tools, just don't know exactly how to use it.

Posted: 11/6/2010 6:40:59 AM EDT

[#6]

This can also be cause by having a firing pin hole that is too large. That means there is excessive space around the firing pin and the primer can flow back into this open area.

As long as the primer is not being "blown out", I wouldn't worry about it too much.

Posted: 11/6/2010 6:41:03 AM EDT

[#7]

A few possibilities.

1. The cartridges are loaded too hot.
2. Firing pin depth is too shallow.
3. Weak firing pin spring.
4. Excessive headspace.

#4 is easy to check with a set of headspace gauges and is a common problem with milsurps.

Best way to check #1 is to fire a few rounds from the same lot in a different rifle and see if a similar cratering effect occurs.

Posted: 11/6/2010 6:43:00 AM EDT

[#8]

Quoted:

Quoted:
Hulls are spent shotgun shells. I'm guessing you have a MN 7.62 x 54R brass shell. Cratering is usually overcharge, but like you mentioned, the pin could be striking a little deep. Did you get one of those screw driver / pin gauge tools with your MN?

sorry about the nomenclature. Yes, I have one of those said tools, just don't know exactly how to use it.

This will show you how to use it: Link

Posted: 11/6/2010 6:49:21 AM EDT

[#9]

http://stevespages.com/diagnosingproblems.html

Posted: 11/6/2010 7:00:09 AM EDT

[#10]

over sized firing pin hole

soft primer cup

headspace

high pressure

take your pick

Posted: 11/6/2010 7:09:36 AM EDT

[#11]

What would other signs of headspace issues be so I know what to look for..... I've had this thing for almost 10 years. This is the first time I've seen it do this.

Also, if rounds were to get submerged in water and MAYBE get a drop or two in there and then dried out for a year, would that make the pressure spike?

The reason I ask is because I had this box of ammo out in the Garage in a plastic foot locker. I had a drainline that decided to spray water everywhere and the footlocker ended up getting a few inches of water in it and these were submerged for a week or two while I was on vacation.

I took out the corroded ones the other day to see if thye would shoot. I didn't notice anything then. Could that possibly do it? Well, that in combination with being stored in a super hot GA garage?

Posted: 11/6/2010 7:15:21 AM EDT

[#12]

High pressure, weak spring, oversize firing pin hole are the leading causes.

Bad head-space is pretty far down the list.

With commercial ammunition in a factory gun look at the firing pin hole first.
They are often much larger than required.

If the gun is worth keeping (accuracy, stock fit, etc.) it is not hard to bush the firing pin hole and drill and ream to a better fit (especially on a bolt action).

Posted: 11/6/2010 7:19:36 AM EDT

[#13]

Quoted:

What would other signs of headspace issues be so I know what to look for..... I've had this thing for almost 10 years. This is the first time I've seen it do this.

Also, if rounds were to get submerged in water and MAYBE get a drop or two in there and then dried out for a year, would that make the pressure spike?

The reason I ask is because I had this box of ammo out in the Garage in a plastic foot locker. I had a drainline that decided to spray water everywhere and the footlocker ended up getting a few inches of water in it and these were submerged for a week or two while I was on vacation.
I took out the corroded ones the other day to see if thye would shoot. I didn't notice anything then. Could that possibly do it? Well, that in combination with being stored in a super hot GA garage?

Maybe, if the powder caked up. What kind of ammo was it, PRVI? I think I would shoot some known decent milsurp or a new box of ammo and see what you get.

Posted: 11/6/2010 7:20:10 AM EDT

[#14]

Quoted:

Quoted:
Hulls are spent shotgun shells. I'm guessing you have a MN 7.62 x 54R brass shell. Cratering is usually overcharge, but like you mentioned, the pin could be striking a little deep. Did you get one of those screw driver / pin gauge tools with your MN?

sorry about the nomenclature. Yes, I have one of those said tools, just don't know exactly how to use it.

This will show you how to use it: Link

Excellent site! I made a "sniper" bolt handle and need to check the firing pin before I fire it and this site will definitely help.

Posted: 11/6/2010 7:23:48 AM EDT

[#15]

Quoted:

What would other signs of headspace issues be so I know what to look for..... I've had this thing for almost 10 years. This is the first time I've seen it do this.

Also, if rounds were to get submerged in water and MAYBE get a drop or two in there and then dried out for a year, would that make the pressure spike?

The reason I ask is because I had this box of ammo out in the Garage in a plastic foot locker. I had a drainline that decided to spray water everywhere and the footlocker ended up getting a few inches of water in it and these were submerged for a week or two while I was on vacation.

I took out the corroded ones the other day to see if thye would shoot. I didn't notice anything then. Could that possibly do it? Well, that in combination with being stored in a super hot GA garage?

Maybe, if the powder caked up. What kind of ammo was it, PRVI? I think I would shoot some known decent milsurp or a new box of ammo and see what you get.

It's S&B 180gr soft points.

I took the bolt apart, did the measurements I was one half turn off. It's back together now. I'm going to take some Russian 80's surplus to the range today to see what happens.....If I get to the range.

Posted: 11/6/2010 7:24:17 AM EDT

[#16]

Never tested it, but I've read excessively lubed chambers can lead to funky looking primers. Based on the theory that the case should grip the chamber somewhat. I always run a patch before shooting.

Posted: 11/6/2010 7:26:14 AM EDT

[#17]

Quoted:

Never tested it, but I've read excessively lubed chambers can lead to funky looking primers. Based on the theory that the case should grip the chamber somewhat. I always run a patch before shooting.

You can KB an AR if you do that to the bolt and chamber...so yeah, it's true.

Posted: 11/6/2010 7:27:50 AM EDT

[#18]

The ammo he is using is rimmed so it headspaces between the bolt head and shell base so I don't think that would affect it like a rimless shell.

Posted: 11/7/2010 6:39:34 AM EDT

[#19]

Well I took it out yesterday to test it out with some surplus. I have some 180 heavy ball. I think it's bulgarian. Brass case and yellow tip projo. Anyway, The primers are slightly cratered. I have noticed before with that type of ammo that the primer pocket would look chared. I couldn't ever tell if it was peirced though. I guess it was. Anyway, I backed off the stiker/firing pin and all is well. It was set too deep to begin with. Thanks for he help guys.

[ARCHIVED THREAD] - What causes primer cratering?

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