Primer seating depth

[higgite]

Whenever the subject of misfires comes up, it most often seems to be attributed to the primer being seated either too deep or too shallow in the primer pocket. I fully understand the problem with seating primers too shallow. The firing pin expends its energy driving the primer further into the pocket instead of crushing the primer and igniting it.

But, I don't understand the other oft stated cause, that is, primers being seated too deep in the primer pocket. How can a primer be too deep in the primer pocket? (Unless the pocket itself is too deep.) Is it not desirable to have a primer bottomed out in the pocket? I have even seen references to some folks seating each primer until they feel it bottom out in the pocket. What am I missing here?

 

[jwrowland77]

I personally when hand priming, make sure that the primer hits bottom. It's the way I was taught and I've never had a primer not ignite from doing so.

The only time I've had a primer not ignite at all after several firing pin strikes, was when I didn't uniform the primer pockets.

 

[Reloadron]

I have even seen references to some folks seating each primer until they feel it bottom out in the pocket.

That would be me.

Primers and primer pockets have prescribed dimensions and tolerances. They can be seen here. That dimensioning also takes into consideration things like firing pin protrusion. There have been several threads on this subject and I believe you will find the general consensus is to seat till the primer "bottoms out" in the pocket. This will generally leave the primer around .003" below the case head.

Ron

 

[Blue68f100]

The proper seating depth is when the primers bottom out in the pocket. No matter what the depth. I have yet to have one fail to fire from being seated to deep.

 

[JohnM]

I'd say the only time you could seat a primer too deep would be in a seriously defective case.

 

[ironworkerwill]

A few weeks ago a THR member had a primer seated too deep. The problem was that the primer pocket was reamed too deeply. The firing pin could not detonate the primer.

I bottom out the primers every time.

 

[LiveLife]

How can a primer be too deep in the primer pocket? (Unless the pocket itself is too deep.) Is it not desirable to have a primer bottomed out in the pocket? I have even seen references to some folks seating each primer until they feel it bottom out in the pocket. What am I missing here?

Not all primer height and pocket depth are the same. And the primer itself has variables of cup shape/height, anvil tip height, amount of priming compound inside the cup/sealant cup and amount of anvil feet below the cup that will "stack" against the variations in the primer pocket depth depending on the brand.

So, seating primers to initial resistance where the anvil feet touches the bottom of the primer pocket and then seating deeper to feel the second resistance where the anvil feet is pressed inside the cup and the anvil tip is set against the priming compound/sealant cup is desired - and at times, seating just to flush does not accomplish this and will require seating the primer cup to slightly below flush.

In the "Tula Primer" thread, the issue of seating depth was tested at length and various brand primers were seated to flush, .004" below flush and .008" below flush - http://www.thehighroad.org/showthread.php?p=7810685#post7810685

Typically, while I prefer to seat primers to .004" which would be the desired seating depth to properly set the anvil tip against the priming compound, primers seated to .008" below flush where the top of the primer cup got flattened, all the primers ignited without issues.

Unless the primer pocket was modified by the reloader to be too deep, I do not think you can seat the primer too deep with factory primer pocket depth.

Comparison picture showing different cup shape and amount of anvil feet sticking below cups

Comparison picture showing different anvil tip height and depending on the amount of priming compound inside the cup/sealing cup, would require different amount of primer seating depth to set the tip against the priming compound

Even with unmodified factory primer pockets, I found the primer pocket depth to vary slightly. Since different brand primers have different length where the bottom of anvil feet protrude in different amount with different anvil/tip height (see comparison picture above showing different cup shape/anvil feet sticking below cup), when using a slightly shorter primer in a slightly deeper primer pocket, due to different anvil tip height to set against the priming compound (which also probably varies), seating primer deeper than typical is required - http://www.thehighroad.org/showthread.php?p=7813399#post7813399

For those wondering why I use .004" below flush as my reference primer seating depth, consider this:

I am averaging around .117"-.118" (with a few variations to .115"-.120") for primer pocket depths for small primer cases (9mm/40S&W). I am measuring .119" for Winchester/Magtech SP primer height and .118" for Tula/PMC SP primers (actual cup height without the anvil feet were same at .109" for Winchester/Tula SP).

This means, depending on primer pocket depth variations, seating primer flush may not set the anvil against the priming compound. Use of .004" below flush is a reference mark for me. When I hand prime the cases, I do it by feel with a QC check by running my finger tip over the seated primer to ensure it is below flush. As I seat the primer, I will initially feel the primer/anvil feet hit the bottom of the primer pocket, then a slight more resistance as the anvil feet is pressed inside the cup and anvil is set against the priming compound.

Because there are variations in primer pocket depths (say .120" deep pocket with shorter .118" height Tula SP primer, to include the anvil feet), flush seating primers may not always ignite. Seating primers to .004" below flush ensures there are no high primers and anvils are properly set against the priming compound.

Forster website has a nice illustration on primer seating depths (scroll down to "Primer On Primer Seating" on the link) - http://www.forsterproducts.com/store.asp?pid=24822

 

[moxie]

Bottoms out/slightly below flush. Works every time. You can "feel" it with a hand primer.

 

[USSR]

Bottoms out/slightly below flush. Works every time. You can "feel" it with a hand primer.

+1. You do NOT seat primers to a particular measured depth.

Don

 

[higgite]

Thanks for all the responses. What I'm hearing is a general consensus that misfires due to "primers seated too deep" are more likely due primer pocket or firing pin issues. I kind of figured that was the case, but wanted some more experienced opinions. I try to seat primers to bottom out, but I know they don't always do so on my progressive press. As long as they are below flush, I haven't had any fail to fire, though.

bds,
Thanks for that link. That's a great thread that I somehow missed when it was current.

 

[gamestalker]

I prime with an RCBS priming die on my press. I set the primer depth to where I can feel it bottom out, and then enough additional depth where I can feel a slight amount of resistance that peaks. Been doing it this way for about 3 decades and I've yet to have a mis fire.

But in this respect, not all primers feel the same when bottoming out as do CCI's. When I'm using Winchester's, they bottom out very abruptly, CCI's have a range beyond initial contact which seems consistent with the shape and design of the primer cup. Whether or not it makes any difference, I've never had a problem to indicate one way or the other.

GS

 

[km101]

I have seated primers until they bottom out for 40 years, and have not had a problem with it. I feel that if it ain't broke, don't fix it.

 

[rcmodel]

You can't seat a primer too deep.
Unless you use excessive force and crush the cup getting it in an un-reamed crimped primer pocket.

In that case, the cup will appear flatter then a high-pressure load before you fire it.

During manufacture:
Primer anvils are seated above the priming compound & foil seal, just slightly into the cup, and sealed in place with colored lacquer to keep them from falling out before they are used.

Then when you seat them bottomed out in the primer pocket, the cup is pressed the rest of the way over the anvil and the point of the anvil is pressed tight against the primer compound pellet.
Probably penetrating the foil seal & lacquer.

That in turn pre-loads the anvil against the primer compound so the dent from the firing pin drives the compound over / against the point of the anvil to concentrate the FP impact against the primer compound to set it off.

Seated too shallow, without the cup in contact with the bottom of the pocket does not pre-load the anvil against the compound.

Seated too deep & crushed flat squishes the primer compound out from between the pointed anvil, and the inside of the primer cup.

You want the cup to just bottom out in the primer pocket to finish pre-loading the anvil into the primer compound, ready to take the FP hit and set it off.

And the best way I have found to do that over the years is with an RCBS hand primer tool.
There are probably better tools today, with better 'feel'?

But I don't know what they are?

rc

 

[Walkalong]

While it can be done, it's hard to "crush" a primer. Seat them firmly to the bottom of the pocket.

 

[LiveLife]

rcmodel brought up a good point that I didn't address in my post and that is primer cup diameter and primer pocket size.

If you use domestic brands like CCI/Federal/Remington/Winchester along with Brazilian Magtech, you are less likely to have this issue but Italian Fiocchi and Russian Tula/Wolf primers (depending on small or large primer) have slightly larger primer cup diameter that takes more effort to seat them fully.

Problem gets worse when you are seating these primers in once-fired brass with tighter primer pockets. With S&B/RWS brass with even tighter primer pockets, larger primer cups won't seat fully and when you increase force, instead of primer cup seating deeper, primer cup simply flattens as expressed by rcmodel. Depending on the headstamp of the brass, even though you firmly seat these primers, you may not be able to seat them even to flush.

However, these primers with slightly larger diameter cups are good for primer pockets that have been enlarged from multiple firings as to extend the useful life of brass.

 

[rcmodel]

+1 bds!

There is more to primer seating then sometimes meats the eye!

But if you are crushing them flat seating them?

You need to stop doing that, and figure out what the problem is.

Because there is a problem.

rc

 

[gamestalker]

Ya, definitely got a problem if your getting flattened primers before pulling the trigger. I've never had a primer seat so hard that it's flattened out, but it would be pretty easy to do with a priming die like I use.

I remember a guy one time bought some CCI-200's that was claiming they were bad. He showed me both the one's that mis-fired, and some he hadn't tried yet, and they were all so over seated, that on the one's he tried to fire, that even if the priming compound was still intact with the anvil, the firing pin was just barely denting the cup, so they probably wouldn't have fired anyway. Poor fellow was brand new into reloading, so I sat him down to the press we had in back and took just a few minutes to teach him what to feel for, look for, all was good next time he came in.

GS

 

[romer12]

seating

have always seated primers at max. depth. never a problem.

 

[Vodoun da Vinci]

One more for "seat it til it bottoms out but do not crush it" school right here. Never had one fail to go bang. I seat them until they bottom out.

VooDoo

 

[spitballer]

I never used to worry about my primers until I started listening to these guys on this website. My primers were always slightly below flush and I never had a problem with them. But after reading thread "pierced primer question" with our go-to professor, ironworker, I've since been insuring that they are in fact bottomed out.

How? Well, at the moment I'm still experimenting with some makeshift seating tools and an arbor press, but for the most part I have been shimming the seating post on my hand primer in an extra operation. It works for small batches like I load but I'd probably invest in a press for larger batches. I gotta admit I feel better about my primers since I have been bottoming them out, although I've never compared them on the chrony. I don't think I'll ever again be satisfied with simply seating them flush.

 

[oldreloader]

rcmodel brought up a good point that I didn't address in my post and that is primer cup diameter and primer pocket size.

If you use domestic brands like CCI/Federal/Remington/Winchester along with Brazilian Magtech, you are less likely to have this issue but Italian Fiocchi and Russian Tula/Wolf primers (depending on small or large primer) have slightly larger primer cup diameter that takes more effort to seat them fully.

Problem gets worse when you are seating these primers in once-fired brass with tighter primer pockets. With S&B/RWS brass with even tighter primer pockets, larger primer cups won't seat fully and when you increase force, instead of primer cup seating deeper, primer cup simply flattens as expressed by rcmodel. Depending on the headstamp of the brass, even though you firmly seat these primers, you may not be able to seat them even to flush.

However, these primers with slightly larger diameter cups are good for primer pockets that have been enlarged from multiple firings as to extend the useful life of brass.

Yep. I agree..I like the Tula primers but you have to seat the LPP with authority.