Primer depth for accuracy

[Straightshooter1]

I suppose a depth mic will be on my list of tools to buy.
Currently uniform at .122 and seat by feel although I just picked up a 21st century click adjustable hand primer that I'm looking forward to trying out.
Definitely easy enough to test a few applications side by side because at 1k everything seems to matters including crushed primers...

A little while back I was shooting with a buddy of mine who goes to great lengths to tune his 6.5CM cartridges, except he was using a hand priming tool and I had my new primer gauge with me. He felt he was getting very consistent seating and thought he could feel whether a primer was seating well or not. So we measured some of his cartridges and to his surprise there were quite a few with significant differences. The majority were within a thousandths or two, but the others were .004 - .005" higher yet still below the case base surface. Soon afterwards, he bought a Primal Right CPS to get the consistency he wants. I just still use my Forster Co-Ax press to seat primers and get very consistent seating where they're all within ~.001 (and I do uniform the primer pockets).

Here the tool I used to make the measurements fast and easy to do:

 

[RegionRat]

Just a suggestion.
To save yourself some confusion if you go down the road to test if this matters, consider inspecting and or correcting the brass up front.

If for example your primer pockets are uniform, then any indications on primer depth are likely valid, the opposite is also true in that if they are irregular or left dirty it is to be expected that some of that seated depth is due to the brass side of the equation.

As always, YMMV.

 

[BoydAllen]

Just a little reality check. A friend owns several world records in short range group. He never brushes the insides of his case necks, and only cleans primer pockets when he happens to think about it. He seats primers by feel with a hand tool. There is no primer depth consistency trophy. We tend to obsess over things that we can measure, whether they matter or not. How many of you own and regularly use wind flags?

 

[mikecr]

If you want learn about this (see it for yourself), get an indicated K&M and test crush for one primer -vs- another. It's the only way you'll come to know the following:
1. Every primer going bang is just the beginning
2. You cannot consistently seat primers by feel
3. You cannot set primer crush without measuring primer crush, which is accounting for primer height to pocket depth -at the same time.
4. Different primers actually have different optimum preloads, with much depending on your striking sys.

 

[gunsandgunsmithing]

If you want learn about this (see it for yourself), get an indicated K&M and test crush for one primer -vs- another. It's the only way you'll come to know the following:
1. Every primer going bang is just the beginning
2. You cannot consistently seat primers by feel
3. You cannot set primer crush without measuring primer crush, which is accounting for primer height to pocket depth -at the same time.
4. Different primers actually have different optimum preloads, with much depending on your striking sys.

Can you explain #2? Number 4 is why I feel that seating by feel is actually best. So, if you mean in #2 that you can't seat to the same depth, by feel, I tend to agree but to the same crush, I'm not so sure. Ultimately, can you quantify the results of seating by feel vs by height or crush, on target? My thinking is, fwiw, that the cup height establishes how much crush, by feel. Seat to the point where the primer bottoms firmly, which is pretty easy by feel, especially in pockets that are less than "tight'(new). It seems logical that bottoming the cup in the pocket would give a very consistent amount of crush.

I look at primer compound like a piece of glass(it contains silica), in that, you can break or shatter the same piece of glass with different force, an/or speed of impact. I feel what we want is to "shatter" it for best and most consistent ignition. We can "break" the compound when seating with too much crush. FWIW, in rimfire, Alan Hall had a super lightweight firing pin in some of his actions. His premise was that we need a fast strike to shatter the compound best. I tend to agree but he may've taken it to extremes. He claimed good ignition with only .002 firing pin indentation on the rim. FWIW, the composition is likely somewhat different but I think cf and rf primer compound are similar to one another and that what's best for one is likely best for both.

It's a good subject and I'm just talking off the top of my head. My thoughts may or may not be right so I'm open to learning more on the subject. I've seen the affects of poor ignition on target. It certainly is more than just going bang.

 

[mikecr]

I'm just suggesting that once you actually measure seating to target preload, you'll notice that feel would have never gotten you there. Each primer/pocket interface is different, different forces, and you cannot 'feel' a movement from bottom to 2thou -vs- 4thou beyond.
Better to watch it with an indicator such as that provided on the K&M.

The K&M is also not a slouch for priming. It has plenty of leverage and you can certainly feel each bottoming touch point. It's design overall should impress you from sound to damn ingenious.
None of the latest and shiniest have managed to top it's function.

 

[Cigarcop]

If you want learn about this (see it for yourself), get an indicated K&M and test crush for one primer -vs- another. It's the only way you'll come to know the following:
1. Every primer going bang is just the beginning
2. You cannot consistently seat primers by feel
3. You cannot set primer crush without measuring primer crush, which is accounting for primer height to pocket depth -at the same time.
4. Different primers actually have different optimum preloads, with much depending on your striking sys.

I just went through this with a customer #2 was his issue, once he measured a few the light clicked on.
#4 is spot on and what I consistently find

I’ve spent enough time to know where I need to be, I think you should try some testing to prove it to yourself one way or the other. JMO

 

[mikecr]

With a Cooper/223Rem I tested FEDs for different crush values, and it turned out that 2thou (as recommended) really was best. 0thou, and 4thou, raised SD.
I swapped to CCIs and found nothing good until 4thou..
No problem, I logged it, that's the way it will be.

But it is interesting that changing preload actually affects ignition, beyond simply going bang.
With other testing I found that attributes of striking played out to affect results, very similar, and again with all primers firing, It's seems an unexplored potential(in a broad sense).

 

[DIBBS]

To toss a curve ball into the equation... maybe... How consistent are primers. Is there primer to primer variation to toss into-add to the seating depth/crush/primer pocket consistency equation.

 

[mikecr]

No matter how good you are with feel, would it benefit over actual measurement?

 

[mikecr]

To toss a curve ball into the equation... maybe... How consistent are primers. Is there primer to primer variation to toss into-add to the seating depth/crush/primer pocket consistency equation.

Yes there is. Primer heights vary. And unless you've cut pockets to same depth, they vary.
The K&M accounts for both at the same time (while seating).

 

[caihlen]

No matter how good you are with feel, would it benefit over actual measurement?

I want to know this too. That is a bunch of variables.

 

[Bill Norris]

To toss a curve ball into the equation... maybe... How consistent are primers. Is there primer to primer variation to toss into-add to the seating depth/crush/primer pocket consistency equation.

Have no clue and not to argue any facts whatsoever but I feel good about my primer seating by feel simply because of the groups I consistently shoot with any of my rifles. I seat all my primers as deep as they will go.

 

[Skeptic123]

I just went through this with a customer #2 was his issue, once he measured a few the light clicked on.
#4 is spot on and what I consistently find

I’ve spent enough time to know where I need to be, I think you should try some testing to prove it to yourself one way or the other. JMO

What I find interesting about this thread is that NO ONE has offered up any actual concrete evidence or test that would demonstrate one way or the other the real effect of primer seating. We don't hesitate to run all kinds of neck tension, annealing, headspace, seating depth, OAL etc. etc. tests. We even run tests using different primers as we know something about them can make a difference. Empirical tests results for almost everything are everywhere. But.....other than Cigarcop.... not one person has offered up actual shooting test results to justify their opinion as to the value of primer seating depth. All in all it shouldn't be that hard to do. I wonder why so few seem to have really investigated this.

 

[gunsandgunsmithing]

What I find interesting about this thread is that NO ONE has offered up any actual concrete evidence or test that would demonstrate one way or the other the real effect of primer seating. We don't hesitate to run all kinds of neck tension, annealing, headspace, seating depth, OAL etc. etc. tests. We even run tests using different primers as we know something about them can make a difference. Empirical tests results for almost everything are everywhere. But.....other than Cigarcop.... not one person has offered up actual shooting test results to justify their opinion as to the value of primer seating depth. All in all it shouldn't be that hard to do. I wonder why so few seem to have really investigated this.

Skeptic, the door is open for someone like yourself to do it and post your results, my friend. There are lots of variables and as Boyd said earlier...how many are using wind flags..

 

[Skeptic123]

I'm working on it as we speak. I was just hoping that I wouldn't have to reinvent the wheel and someone would have done the work for me. lol And fyi I do have and use wind flags. There are big pieces and little pieces to the puzzle but in the end they all move us closer to the ultimate goal.

 

[newbieshooter]

What I find interesting about this thread is that NO ONE has offered up any actual concrete evidence or test that would demonstrate one way or the other the real effect of primer seating. We don't hesitate to run all kinds of neck tension, annealing, headspace, seating depth, OAL etc. etc. tests. We even run tests using different primers as we know something about them can make a difference. Empirical tests results for almost everything are everywhere. But.....other than Cigarcop.... not one person has offered up actual shooting test results to justify their opinion as to the value of primer seating depth. All in all it shouldn't be that hard to do. I wonder why so few seem to have really investigated this.

Bart's test (post #11) doesn't count?

 

[gunsandgunsmithing]

I think a good chrono should be all that's needed to give good evidence. Perhaps it's been done, but I'd think, work up your best load, with low es, then do all the prep and measuring on half of your lot of brass and shoot round robin over the chrono. Should give a solid number in respect to es, at least.

 

[gunsandgunsmithing]

Bart's test (post #11) doesn't count?

I should've looked at that first. Looks like he did similar to what I'm referring to. Sure, his test should count. It'd be nice to see some actual numbers put to it but ultimately, we have to be able to shoot the difference. It always boils down to that but making every effort to be better doesn't hurt either.

 

[gunsandgunsmithing]

My biggest question relates to just how we go about measuring the actual crush amount. Sure, we can uniform pockets and measure the depth below flush, but if the primers have some variation as well...do we measure each primer, both cup and overall, or what? I don't think we can get the full story by measuring how deep from flush.