Firing Pin Bumping Shoulder?

[Florida Wally]

I’m shooting 308 with a newish (250 rounds on it) Panda Action. I have a some Alpha OCD brass that was once fired and annealed. I am using a Benchsource flame annealer which I have been using for Lapua brass. Well, the Alpha brass is thinner than Lapua and I got the cases so hot I noticed a pinkish copper color on the neck after the brass cooled, only the neck, not the shoulder. I was able to wipe the pinkish color off with scotchbright. I was going to load these cases for a match this weekend so I loaded three cases with BR4’s, Varget and Juggernauts just to test them before I loaded them all. The cases were full length sized with 0.001” shoulder bump. The first two shot no problem, but the third was a misfire. The firing pin hit the primer, dimpled it, but the primer did not go off. I pulled the bullet and the powder wasn’t burned and I deprimed the case and hit the primer with a hammer and it went off. I wasn’t sure and am still not sure what happened. I first thought that that the primer was bad, that’s why I hit it with a hammer. Since it went off, I’m thinking it was okay. I have had a primer from the same lot fail to fire a while back. I then measured the case and it now has a 0.003” shoulder bump, almost like the firing pin bumped the shoulder 0.002”. I first thought that I softened the shoulder so much that it gave way and caused a light primer strike. I then sized and primed four more cases from the same lot and shot them without powder or a bullet and measured the headspace with my RCBS Precision Mic headspace gauge. All of them fired. I then sized and primed a Lapua SRP case with a BR4 from the same brick, no powder or bullet and it fired. The headspace decreased on each of the four OCD cases and the Lapua case by 0.002” to 0.003”. Finally, I dry fired a few OCD cases from another lot that had been fired and the spent primer was still in them. Same thing, the firing pin seemed to bump the shoulder 0.002” to 0.003”.

I’m now thinking I just had a bad primer and my cases are fine even after getting so hot. Has anyone measured a case before and after dry firing and does the firing pin bump the shoulder back?

Are there any other thoughts as to what may have happened? Sooner or later I will have a chance to load and shoot some more of the pink neck brass and ultimately get to the bottom of this.

Edit: I should have mentioned that the bullet seating force was the same as I usually have with the OCD brass when I seated the bullets in the pink neck brass. I measure with the K&M arbor press with the standard force pack.

 

[Ned Ludd]

I have never measured the effect of a primer strike on the cartridge base-to-shoulder (CBTS) measurement. Not that I don't find the notion interesting, it just never occured to me. Obviously when the cases from loaded rounds that ignited properly are measured, one might typically observe an increase of .001" to .002" in CBTS, assuming that is the amount the shoulder was pushed back during the previous re-sizing step. It sounds from your subsequent experiments/tests that the observed shoulder bump from the primer strike was not dependent on a potential state of "over-annealing", correct? As I noted, this is not something we would or could ever typically measure if the loaded round fired as it was expected to do. Maybe the firing pin strength is sufficient to do this, even though I would have thought the dimpling of the primer cup would absorb a fair amount of the strike energy. Clearly the primer strike can be sufficient to drive the case forward in the chamber when there is sufficient headspace for it to move.

Some questions arise from your observations: did the firing pin strike appear noticeably "light" on the primer that failed to detonate? If the strike was visibly light, then there might be something to the softened shoulder idea. However, I suspect it was more likely an issue with that one primer as your subsequent primer tests all fired. Do you use Lemishine at any point in your brass cleaning process? I have observed with my brass that if it generates the slightly pinkish tinge on the necks after annealing, it has usually been over-exposed to Lemishine/citric acid during cleaning. In that event, the color change is due to a redox reaction, not because any copper has been "smelted" out of the neck during the annealing process. The fact that you were able to wipe the pink color off is consistent with this notion. I mention this only because it is quite possible you did not over-anneal the brass; or at least, over-annealing was not necessarily the cause of the pickish tinge.

In your shoes, I would probably continue to use the brass without any major concern, but with the idea that if a few more primers fail to fire, you may have to do something about it. I'm not really sure what else you can do about it at this point. I also use both Lapua and Alpha SRP .308 Win brass. In my hands, the Alpha brass is noticeably heavier than Lapua, and if anything, the necks appear to be a tad thicker. I wouldn't think they are markedly thinner, so hopefully your brass is fine and you just had a bad primer...it happens.

 

[Webster]

I’m shooting 308 with a newish (250 rounds on it) Panda Action. I have a some Alpha OCD brass that was once fired and annealed. I am using a Benchsource flame annealer which I have been using for Lapua brass. Well, the Alpha brass is thinner than Lapua and I got the cases so hot I noticed a pinkish copper color on the neck after the brass cooled, only the neck, not the shoulder. I was able to wipe the pinkish color off with scotchbright. I was going to load these cases for a match this weekend so I loaded three cases with BR4’s, Varget and Juggernauts just to test them before I loaded them all. The cases were full length sized with 0.001” shoulder bump. The first two shot no problem, but the third was a misfire. The firing pin hit the primer, dimpled it, but the primer did not go off. I pulled the bullet and the powder wasn’t burned and I deprimed the case and hit the primer with a hammer and it went off. I wasn’t sure and am still not sure what happened. I first thought that that the primer was bad, that’s why I hit it with a hammer. Since it went off, I’m thinking it was okay. I have had a primer from the same lot fail to fire a while back. I then measured the case and it now has a 0.003” shoulder bump, almost like the firing pin bumped the shoulder 0.002”. I first thought that I softened the shoulder so much that it gave way and caused a light primer strike. I then sized and primed four more cases from the same lot and shot them without powder or a bullet and measured the headspace with my RCBS Precision Mic headspace gauge. All of them fired. I then sized and primed a Lapua SRP case with a BR4 from the same brick, no powder or bullet and it fired. The headspace decreased on each of the four OCD cases and the Lapua case by 0.002” to 0.003”. Finally, I dry fired a few OCD cases from another lot that had been fired and the spent primer was still in them. Same thing, the firing pin seemed to bump the shoulder 0.002” to 0.003”.

I’m now thinking I just had a bad primer and my cases are fine even after getting so hot. Has anyone measured a case before and after dry firing and does the firing pin bump the shoulder back?

Are there any other thoughts as to what may have happened? Sooner or later I will have a chance to load and shoot some more of the pink neck brass and ultimately get to the bottom of this.

Edit: I should have mentioned that the bullet seating force was the same as I usually have with the OCD brass when I seated the bullets in the pink neck brass. I measure with the K&M arbor press with the standard force pack.

The only primers I ever had that didn't fire were ones that I didn't seat to the bottom of the pocket. Are you seating to a certain depth and not by feel.

 

[calgarycanada]

I have had that happen to brand new Starline 5.56 brass. I decided to load subsonic loads for plinking. When I measured them afterwards, case base to shoulder length decreased by 3-4 thou when compared to other unfired brass from same lot. This was in Barnard action.
BTW they all fired fine, just that pressure wasn’t high enough to expand them to chamber.

 

[NZ_Fclass]

Not casting shadows - but more likely the case was bumped too far when sizing. Possibly caused by annealing too far - or not enough - causing inconsistent spring back

 

[searcher]

Most failure to fire situations are due to excessive shoulder space in the chamber. If your firing pin is, as you said, bumping the shoulders .002" to .003", it is conceivable that you did get the shoulders so hot they are just "collapsing, so to speak, and absorbing the energy that would have otherwise been directed into the primer. If you had the cases glowing as you note - they likely did get way too hot - and too soft. Still, having .003" "headspace" and having the shoulders knocked back another .002" to .003", I'd think they would still fire - but that would depend on your firing pin protrusion. Is it possible you are bumping the shoulders on cases that are not entirely blown forward? Sometimes it is a combination of things that create the excessive shoulder space - even levelling primer pockets can add to that situation, cumulatively.

 

[Florida Wally]

I have never measured the effect of a primer strike on the cartridge base-to-shoulder (CBTS) measurement. Not that I don't find the notion interesting, it just never occured to me. Obviously when the cases from loaded rounds that ignited properly are measured, one might typically observe an increase of .001" to .002" in CBTS, assuming that is the amount the shoulder was pushed back during the previous re-sizing step. It sounds from your subsequent experiments/tests that the observed shoulder bump from the primer strike was not dependent on a potential state of "over-annealing", correct? As I noted, this is not something we would or could ever typically measure if the loaded round fired as it was expected to do. Maybe the firing pin strength is sufficient to do this, even though I would have thought the dimpling of the primer cup would absorb a fair amount of the strike energy. Clearly the primer strike can be sufficient to drive the case forward in the chamber when there is sufficient headspace for it to move.

Some questions arise from your observations: did the firing pin strike appear noticeably "light" on the primer that failed to detonate? If the strike was visibly light, then there might be something to the softened shoulder idea. However, I suspect it was more likely an issue with that one primer as your subsequent primer tests all fired. Do you use Lemishine at any point in your brass cleaning process? I have observed with my brass that if it generates the slightly pinkish tinge on the necks after annealing, it has usually been over-exposed to Lemishine/citric acid during cleaning. In that event, the color change is due to a redox reaction, not because any copper has been "smelted" out of the neck during the annealing process. The fact that you were able to wipe the pink color off is consistent with this notion. I mention this only because it is quite possible you did not over-anneal the brass; or at least, over-annealing was not necessarily the cause of the pickish tinge.

In your shoes, I would probably continue to use the brass without any major concern, but with the idea that if a few more primers fail to fire, you may have to do something about it. I'm not really sure what else you can do about it at this point. I also use both Lapua and Alpha SRP .308 Win brass. In my hands, the Alpha brass is noticeably heavier than Lapua, and if anything, the necks appear to be a tad thicker. I wouldn't think they are markedly thinner, so hopefully your brass is fine and you just had a bad primer...it happens.

Yes, based on the few test firings of primed cases, I ruled out over annealed shoulders. The test firing with the Lapua brass, although only one test sample, got me thinking that the force of the firing pin alone can bump the shoulders, unless I over annealed the Lapua shoulders as well. I have annealed thousands of Lapua cases to a similar degree. I have always annealed my cases until I see a salmon color to the bottom of the case neck before removing it from the flame. i have just started using Alpha brass due to the unavailability of Lapua Palma brass. I note that the Alpha brass is thinner since I must use a .334” bushing to get some resistance with a .3065” mandrel, whereas with Lapua, I use a .336” bushing. I assumed the Alpha was thinner, but it may not be. I’ll measure a loaded case for each and compare. I only briefly looked at the primer strike, but it didn’t seem any different than the other primers that were fired. Unfortunately, I did not take a picture of it before hitting it with the hammer. I dry tumble in rice, so no Lemishine. The pinkish color appeared only after annealing and gave me cause for concern. I agree, I think the brass will be fine.

 

[Florida Wally]

The only primers I ever had that didn't fire were ones that I didn't seat to the bottom of the pocket. Are you seating to a certain depth and not by feel.

Yes, 0.005” below flush. The primer pocket depth is the same measurement as the height of the primer. I am using 20th Century seater.

 

[Florida Wally]

I have had that happen to brand new Starline 5.56 brass. I decided to load subsonic loads for plinking. When I measured them afterwards, case base to shoulder length decreased by 3-4 thou when compared to other unfired brass from same lot. This was in Barnard action.
BTW they all fired fine, just that pressure wasn’t high enough to expand them to chamber.

The more I think about the force applied by the firing pin spring, the more I think it is a normal occurrence. Glad to hear someone else had the sale result.

 

[Florida Wally]

Most failure to fire situations are due to excessive shoulder space in the chamber. If your firing pin is, as you said, bumping the shoulders .002" to .003", it is conceivable that you did get the shoulders so hot they are just "collapsing, so to speak, and absorbing the energy that would have otherwise been directed into the primer. If you had the cases glowing as you note - they likely did get way too hot - and too soft. Still, having .003" "headspace" and having the shoulders knocked back another .002" to .003", I'd think they would still fire - but that would depend on your firing pin protrusion. Is it possible you are bumping the shoulders on cases that are not entirely blown forward? Sometimes it is a combination of things that create the excessive shoulder space - even levelling primer pockets can add to that situation, cumulatively.

I do not believe I have excessively bumped the shoulders since the bolt with the firing pin removed will not close freely on an unsized case. After I size and bump the shoulder back 0.001” the bolt handle drops freely. I only bump ~0.001”, not 0.002“ to 0.003”. The 0.002” to 0.003” in my post was in reference to what I noticed as additional bump after dry firing.

 

[Doom]

If the round doesn't fire first time, reload it and try again. If it fires the primer wasn't seated deep enough to crush the anvil into the primer pellet.

 

[jrb06]

Not that I doubt what you are saying as you have used sound means to measure and compare and don't have an answer, but think about what it takes to bump a shoulder back in a die. If a firing pin can do this why would you need lube and the leverage of the press to bump it back? I understand the lube is more for the case diameter but the force to bump the shoulder is not light.

 

[JB10]

I ran into same issue under different situations. I had a 6x45 built, first time out with f/l sized brass was just fine. Next trip had lots of misfires. When i did lots of measuring i found shoulders were pushed back upwards of .005 from some other cases. And ones i tried to fire several times were .006. In my case guys i talked to said since i was necking up my brass to 6mm and needed to fire form i needed to not bump shoulders to begin with or seat bullet touching lands so brass would not move forward during firing so primer gets hit hard enough. This was with cci 450 primers. I though about trying another primer but worked around it with what i was told to try first.

 

[TaperPin]

Others have been puzzled how the RCBS headspace gauge could show fire forming loads shrinking the case, so you aren’t alone.

I don’t know the shape of the gauge or if it tends to contact a shoulder evenly, on the outermost edge or near the neck/shoulder junction.

Could it be the shoulder isn’t being pushed back, but rather the outermost edge of the shoulder (where the headspace gauge makes contact) is being slightly rounded over as it contacts the chamber? A .001” roundover on the sharpest part of the shoulder may fool the gauge and read .0015” short depending on the shape of the contact surfaces.

Very interesting issue.

 

[Florida Wally]

Others have been puzzled how the RCBS headspace gauge could show fire forming loads shrinking the case, so you aren’t alone.

I don’t know the shape of the gauge or if it tends to contact a shoulder evenly, on the outermost edge or near the neck/shoulder junction.

Could it be the shoulder isn’t being pushed back, but rather the outermost edge of the shoulder (where the headspace gauge makes contact) is being slightly rounded over as it contacts the chamber? A .001” roundover on the sharpest part of the shoulder may fool the gauge and read .0015” short depending on the shape of the contact surfaces.

Very interesting issue.

Excellent point! I’ll take a look at the gauge and find where the contact point on the shoulder is when I get home today.

 

[searcher]

I do not believe I have excessively bumped the shoulders since the bolt with the firing pin removed will not close freely on an unsized case. After I size and bump the shoulder back 0.001” the bolt handle drops freely. I only bump ~0.001”, not 0.002“ to 0.003”. The 0.002” to 0.003” in my post was in reference to what I noticed as additional bump after dry firing.

With a tight round and only got a dimple on primer, that narrows it down some - pretty much excludes headspace issues, I'd think. I'd disassemble bolt and clean/lube, check primer pocket depth on the round that dimpled if you know which one it was. Figure either something stopped the firing pin from fully extending - or it did extend and something created excessive distance on that round between firing pin and primer. Has to be one of the two with only a dimple.

 

[MislMan]

Buy some factory ammo. Take copious measurements and pics. Fire said ammo and see if you get the same results. This takes your prep and reloading efforts out of the guessing.

 

[Mastershot]

If you have fired brass that has the shoulders too far back, your only fix is to jam the bullets and re-fire form them. Use a de-capper die to remove the primer and take measurements. This might take a few firings to get the shoulders back. I always check my brass on re-sizing on bolt close against fired brass. I generally run 1.5 to 2 thou set back on the brass.

 

[Florida Wally]

Others have been puzzled how the RCBS headspace gauge could show fire forming loads shrinking the case, so you aren’t alone.

I don’t know the shape of the gauge or if it tends to contact a shoulder evenly, on the outermost edge or near the neck/shoulder junction.

Could it be the shoulder isn’t being pushed back, but rather the outermost edge of the shoulder (where the headspace gauge makes contact) is being slightly rounded over as it contacts the chamber? A .001” roundover on the sharpest part of the shoulder may fool the gauge and read .0015” short depending on the shape of the contact surfaces.

Very interesting issue.

Well, I measured the ID of the gauge with my calipers and it was 0.400”. I then locked the calipers at 0.400” and then slid them down the shoulders and 0.400” is just about in the middle.

 

[Bill K]

I can't see how the firing pin strike could push the case forward from it's hold by the extractor and bolt face.
Sound more like a headspace issue with your rifle to me. But I sure can learn something new, I guess.