Primer cratering

[ElJay]

I have a brand new Savage Model 12 Long Range Precision Varmiter that craters primers in both factory ammo and hand loads that are well within published maximum pressures. Other than high pressures, what can cause primer cratering? Is this something that I should be concerned with?

ElJay

 

[25AI260]

taking a stab.... 1st an my guess is- you could have soft primer cups ... like cci400 some mine have punch threw..

guessing.... but probablly not
more technical hole is to large.. firing pin to long .. headspace a bit long

 

[nbkky71]

The only thing that comes to mind (other than excessive pressure) is an oversized firing pin hole.

 

[bheadboy]

this happeing with factory, i would send sample brass to Savage and ask their responce

Bob

 

[SmokinJoe]

Send the bolt to Gre-Tan Rifles & have it bushed & your problem will be solved. If yours is like mine was, the firing pin hole actually had a tiny radius, like a bevel. I attributed that to the probable manufacturing of the bolt head from investment castings. Nothing really wrong with that, but they just can't hold as tight a tolerances without additional machining designed in, which is not the direction they're trying to go.

 

[nosualc]

Savages have sloppy firing pin holes. As long as you're not piercing primers, I wouldn't worry about it.

If it really concerns you, send your bolt to Gre-Tan rifles to have the firing pin bushed. It's cheap, and the turn around time is just a few days.

-nosualc

 

[markm87]

Every one of our factory bolt guns seems to do this... especially the Rem 700s.

Since they're not piercing, I haven't had any urge for the aftermarket fix.

 

[ElJay]

Hey guys- Thanks for the replies. It seems that disregarding the cratering that is probably due to sloppy firing pin clearance is probably OK. What then would be the next sign or signs of over pressure I should be concerned with during load development?
I am very new to this game and the advice I have gotten on this forum from guys like MarkM87 and others has been invaluable. I made it through Vietnam with no problems but this over pressure thing is always on my mind. I'd like to live another 70 years with all my parts.

 

[nosualc]

Hey guys- Thanks for the replies. It seems that disregarding the cratering that is probably due to sloppy firing pin clearance is probably OK. What then would be the next sign or signs of over pressure I should be concerned with during load development?
I am very new to this game and the advice I have gotten on this forum from guys like MarkM87 and others has been invaluable. I made it through Vietnam with no problems but this over pressure thing is always on my mind. I'd like to live another 70 years with all my parts.

Trying to keep all your parts intact is a laudable goal!

Primers usually aren't a very dependable sign of pressure IMO. Too much variance between brands (eg - Federal vs CCI vs Wolf, etc.). Flattened primers is another indicator I'd put into this same category. For example, Federal primers are kinda soft and tend to crater and flatten quite a bit even at safe levels.

Sticky bolt lift, and ejector hole marks on the case are my favorite early warning signs. Loose primers (eg - primers that fall out), or blown primers is the next level of trouble. A chrono is usually a good tool to help too. Start getting over book max speeds and you should proceed with extreme caution.

Best thing to do is start low and work your way up gradually. As soon as you see real signs of over pressure, back off. It's been my experience that my most accurate loads aren't the hottest.

-nosualc

ps - Thankyou for your service

 

[effendude]

Eljay,
Get the firing pin bushed at Gre-Tan or by another competent smith. Risking your eyesight with a potential pierced primer isn't worth it.
Scott

 

[6BRinNZ]

Hey guys- Thanks for the replies. It seems that disregarding the cratering that is probably due to sloppy firing pin clearance is probably OK. What then would be the next sign or signs of over pressure I should be concerned with during load development?
I am very new to this game and the advice I have gotten on this forum from guys like MarkM87 and others has been invaluable. I made it through Vietnam with no problems but this over pressure thing is always on my mind. I'd like to live another 70 years with all my parts.

Eljay - the thing to remember with pressure is without a strain gauge you're only ever working with indicators of pressure, some of them have their own causes that aren't necessarily pressure related. Typically pressure goes hand in hand with velocity and IMO Nosualc (Nosualc post makes a lot of sense) really hits the nail on the head there by suggesting that a chrony is a good guide. It is perfectly possible in a modern action/rifle (I mean custom more than factory but...) to have none of the traditional indicators but be well into high pressures, but this would be indicated by very high velocities.

Traditional indicators are - primer flattening, primer cratering, sticky bolt lift, loosening primer pockets, ejector marks, expanding case bases and arguably excessive speed...without a chrony this might appear as a sudden much higher impact on target. Any one of these indicators may/may not mean that you have a load related pressure issue, but more than one together and you had better take lots of notice.

IMO - when the harder primers are starting to crater significantly in an unbushed bolt you are probably starting to get up towards the higher end but still safe pressures as indicated by quickload. With an unbushed bolt face it is possible to get a small amount of cratering with a mild load and hard primers if you oversize the case (push the shoulder back little too far) a little and/or leave lube on the case.

I have attached a picture of primers - see if you think they are over pressure, under pressure, or just right.

And finally - always wear safety glasses - sometimes sh1t happens no matter how careful you are or how mild your load.

 

[Joe O]

My LRPV was real bad.I emailed a pic to customer service and they sent a UPS pick up order for the gun,the next day.They installed a new bolthead,which took care of the problem.

 

[ElJay]

6BRinNZ,
I do have and use a chrony and have never seen excessive velocities or any of the other high pressure indicators you and others have mentioned. As I said in my original post, I have only seen primer cratering with my new Savage M12 and that was with both factory and hand loaded ammo. As soon as the thrill of shooting very small groups with this gun wears off, I will send the bolt out to get the firing pin hole bushed.
To my inexperienced eye, I see little difference in the six case heads in the picture. If there are major indicators there, I need a lot more help.
Can you tell me more about actually measuring pressure and how it is done?

JoeO- Do you still have the picture?I'd love to see it.

Regards,

Leigh

 

[itchyTF]

ElJay,

Here is one tool to monitor pressure (I have one). I'm not sure how well you can depend on it giving you absolute pressure without a means to calibrate it, but it's certainly good for comparisons.

+1 on your service.

http://www.shootingsoftware.com/pressure.htm

 

[timeout]

I have a 6BR that was purchased used. I noticed the primers looked funky from day one. I shoot mild loads and was not concerned until I pierced some primers. The primers were CCI. Switched back to Fed match primers and never had another primer failure. I just sent the bolt to Gre-Tan for repair becuase I prefer to have mechanical things work correctly. I am guessing that you could use certain brands of primers and not have failures, just not the way I would leave it.

Thanks for your service!

 

[SmokinJoe]

6BRinNZ, those look very similar to my 30BR competition loads using Wolf SRM primers, and that is a warm load. My load shoots a BIB 118 10 ogive @ ~3,050 fps.

 

[6BRinNZ]

SmokinJoe - you're the closest yet with respect to warm load - they're from 6br shooting 105grn - here is the interesting part. No sticky bolt lift or any other indicator of pressure (base was measured later and it had expanded .0005), other than extreme velocity 3020 fps in a standard 6br - turns out there was 32.5 grains of varget in there....I think quickload puts it round 72000psi....scary.
I found it interesting that you picked up that it was a warm load as to most peoples eyes the primers still have a nice radius and aren't particularly flat and cratering is almost non existent.

Eljay - yeah not saying you re doing anything wrong or have an issue just responding to your "new to this game" comment. I loaded the pic simply to make the point that what we mostly use as indicators is not the real picture and often the symptoms can be masked, especially in modern actions with no ejectors, hard primers etc etc. Its easy to go down this path trying to squeeze a little more fps out of the load. The pics are the flip side to the fact that primer cratering has a lot of non pressure related causes.

 

[Matt Pitchon]

PTG makes a replacement bolt head that solves the sloppy firing pin problem. There is an article in the Riflemans Journal:

http://riflemansjournal.blogspot.com/2012/06/good-stuff-ptg-bolt-head-for-savage.html


It discusses the Savage bolt head in detail.

 

[SmokinJoe]

Question - Are those Wolf SRM, or what? 72K is a bit over the top, yes! Though I think a lot of 60-65K loads are used in Lapua brass & tight actions routinely. We are fortunate to have such good components.

 

[6BRinNZ]

Question - Are those Wolf SRM, or what? 72K is a bit over the top, yes! Though I think a lot of 60-65K loads are used in Lapua brass & tight actions routinely. We are fortunate to have such good components.

Sorry - meant to state that - cci450s. Yeah I suspect that it is in the high 65k range ...although its so hard to tell...to me a standard 6br doing over 3000 fps is either an incredibly fast barrel or way over pressure. They were fired in a BarnardP action which is massive in its engineering compared to the case, so I'm not sure if that has helped keep things under control although over pressure.