Measuring primer seating depth.


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Alabama2010
April 23, 2010, 01:03 PM
To preface the following, I just want to state that I don't have any kind of primer seating issue so I'm not looking for advice exactly. I've read many posts where people make references to measuring their primer seating depth and was wondering how they did it.

I personally seat my primers as far in as they'll go. Looking under a magnifying glass, I can see that they seat a little below the bottom of the case. That simple observation is all I can do.

How do you quantitatively measure the seating depth with calipers? Or is there another tool that's used? Seems to me that using standard calipers would leave a huge margin for error. Additionally- is it even necessary?

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Dave P
April 23, 2010, 01:15 PM
The lower end of all calipers are designed to measure depth (AFAIK). I stick that tailend on the primer, and the two main legs/scales on the case head . Simple.

Maybe not accurate, but good enough for most of us.

rcmodel
April 23, 2010, 01:28 PM
I fail to understand how measuring would tell you anything useful.
Unless all you used were match prepped cases with uniformed primer pockets.
And all the primers were from the exact same lot number.

What is important is that every primer is seated fully to pre-load the anvil into the compound, and every one is seated below level with the case head.

I do that by feel with an RCBS hand primer tool when seating.
Then run my finder over each one to make sure it isn't sticking up.

What each one actually measures in thousandths of a knats azz is meaningless to me.

rc

The Bushmaster
April 23, 2010, 01:31 PM
By feel...As I remove them from my Lee Auto prime II I run my finger over the primer and it tells me if the primer is below the case head.

If you lay two different thickness paper side by side and run your finger over them you will find that you can feel the difference of less then .001 of an inch.

I also SEAT my damned primers...

Asherdan
April 23, 2010, 01:32 PM
I do the same as Dave P to check 'em. If I remember right (which means you might want to check your ownself), the recommendation from Lyman's 48th was .004" depth. I use a hand tool to seat primers so I have a good feel for them being well in the pocket, I've had some brass that won't let the primers seat that deep but firmly seated and at least .002" deep on a spot check with my calipers has been my minimum guide.

Of course, I did that when I was starting out so I'd know what I was seeing and feeling measured within the recommended spec.

Now I fully smoosh them in and run a finger over the pocket to make sure it feels right and carry on, as rc and bushmaster say.

The Bushmaster
April 23, 2010, 01:33 PM
Darn it! rc...Take a coffee break so I can beat you to the posting...Either that or type slower...

Walkalong
April 23, 2010, 02:20 PM
I fail to understand how measuring would tell you anything useful ...................... ..................................I do that by feel with an RCBS hand primer tool when seating. Then run my finder over each one to make sure it isn't sticking up.Same here.

Jesse Heywood
April 23, 2010, 03:11 PM
Using a 6" caliper to measure the depth of a seated primer is an exercise in futility. To get an accurate measure you need to use a depth gauge micrometer. But it isn't necessary, unless you are needing bench rest accuracy.

I used to use my fingertips, but recently found that mine are not as sensitive as they used to be. (Must be due to the computer!) So I came up with a nail test. I run the cartridge head over the end up the nail on my forefinger or thumb. If the nail hangs on the primer, it gets rejected faster than the geek asking for a date with the homecoming queen.

JimGun
April 23, 2010, 04:57 PM
Whether you measure or feel, the primer must be below the case head. I lost all my reloading equipment in Hurricane Ike and when my new hand loader came, I found myself having to pull the trigger twice before the round would fire. I had never incurred the problem before and was “advised” that I wasn’t seating the primer enough. I talked to RCBS and they suggested that the problem may be that the link follower in the hand primer was too short an sent me another one, free of charge. That corrected the problem. However, ever since I always feel the primer once seated.

MachIVshooter
April 23, 2010, 06:20 PM
This:

What is important is that every primer is seated fully to pre-load the anvil into the compound, and every one is seated below level with the case head.

I do that by feel with an RCBS hand primer tool when seating.
Then run my finder over each one to make sure it isn't sticking up.

What each one actually measures in thousandths of a knats azz is meaningless to me.

I have never measured primer seating depth. It's easy to tell visually if they're not seated at least level with the case head, and that's the only time it can be problematic. Otherwise, with a hand priming tool, you can definitely feel when they hit home. I give 'em just a little more squeeze after I feel that to be sure.

bds
April 23, 2010, 06:27 PM
I used to seat the primers in the progressive press - I thought if they were flat with the case bottom, they were good enough.

Well, after enough rounds that fired on the second strike I realized they weren't seated fully and the first strike was pressing the primers deeper.

Since I started hand priming, failure-to-fire is now a distant memory and my fingers can "feel" the primers seating just slightly below the case bottom.

The Bushmaster
April 23, 2010, 10:01 PM
MachIVshooter...measuring the primer depth will not insure that the primer is seated all the way and armed.

parker51
April 23, 2010, 10:49 PM
I never measured mine, I just seated them as deep as I could using a RCBS Hand Primer. I had never experienced any problem doing it this way until last week. I was priming some Remington 7mm mag brass using the recommended shellholder (#4) and noticed the primers were protruding just slightly above the bottom of the case. Since this was the first time priming 7mm magnum cases I figured they must be seated properly since I had sqeezed the priming tool handle as far as it would go. I decided to try a couple of the pieces of brass in the gun and found that the primers were scratched from hitting the bolt face or firing pin. Anyhow, I discovered the problem was there was too much play in the shellholder and I had to reseat a couple hundred primers with my press. I called RCBS and they said to return the shellholder to where I bought it and to try another number (#26 I believe).

MachIVshooter
April 23, 2010, 11:53 PM
MachIVshooter...measuring the primer depth will not insure that the primer is seated all the way and armed.

I know. And I don't measure them. Just ram 'em home with the RCBS hand priming tool.

Leaky Waders
April 24, 2010, 01:10 AM
Primer seating depth is one of those measurements that confuse us new reloaders...you're trying to do everything 'right' and read the texts and after shooting your first batch and having a few misfires or rounds that needs struck you quickly learn that primer seating depth = all the way in.

James2
April 24, 2010, 01:36 AM
Hmmmm, a lot of to-do over nothing. Press them in until they hit bottom. Done.

jcwit
April 24, 2010, 07:59 AM
Very simple to know if primer is deep enough, and if you don't trust the "feel" with your finger.

1. Seat Primer
2. Set shell casing on flat surface with primer down
3. If shell casing rocks & rolls, primer is not deep enough

There you go boys & girls.

bds
April 24, 2010, 12:23 PM
1. Seat Primer
2. Set shell casing on flat surface with primer down
3. If shell casing rocks & rolls, primer is not deep enough
Actually, this test won't help with some newer Speer/CCI cases as the center of the case bottom, where the primer pockets is located, is lower/deeper than the case bottom rim. I have intentionally seated primers "high" in these cases and although the primer sticks above the case bottom, they do not "rock and sway" when placed flat on the bench.

Remember that a primer seated "flush" with the case bottom IS NOT seated all the way in. If you don't believe me, just check the primers on the new factory ammunition - you will find them all to be just slightly below the case base bottom.

I loaded 1500 cases yesterday for a range practice/test load session for today and thought I compare the press priming vs hand priming. Even though I pressed "hard" on the ram lever on my Pro 1000 press to seat the primers, 2/3 of the primers came out about flush with the case bottom and 1/3 just barely below the case bottom. However, all the cases I hand primed resulted in primers seated below the case bottom. This is one of many reasons why I hand prime all of my pistol cases now - no more failure-to-fire.

Some will undoubtedly argue that their flat/flush seated primers fire fine without any problems. I would agree IF your combination of soft brass/bronze cupped primers and hard hammer/striker spring provides enough force to ignite the primer that is not fully seated. But if you use harder nickel plated primer cup and have softer hammer/striker spring, first strike will only seat the primer deeper and not ignite it.

For me, since I load for multiple pistols, I make it my standard practice to produce rounds that will ge "bang" no matter what pistol they are fired in. It is for this reason why all of my cases get full-length sized, minimally flared/taper crimped to fit the tightest chambers and primers seated below the case bottom.

For you, if the flush seated primers fire fine in your pistols, great. If you have primers that fail to ignite on the first strike, seat them deeper. :D

918v
April 24, 2010, 12:43 PM
I hand seat my primers with a Hornady tool. I don't measure the seating depth. I feel the primer bottom out against the bottom of the primer pocket. That is the correct seating depth- when you feel the feet of the primer anvil bottom out and then just a bit more to preload the priming mix as BDS described above.

Dave P
April 24, 2010, 01:09 PM
Some of you scoff at measuring the depth, but it is an important safety issue when shooting Garands and M14's and such, with floating firing pins.

Having a recessed primer ( because you standardized each case with your deluxe pocket reamer tool) makes the round more resistant to a slam fire from the firing pin slamming into it when the bolt closes.

I am not sure of the preferred depth, but mine measure about 8 mils below the head.

The Bushmaster
April 24, 2010, 02:53 PM
8mm?

918v
April 24, 2010, 03:15 PM
Some of you scoff at measuring the depth, but it is an important safety issue when shooting Garands and M14's and such, with floating firing pins.

Having a recessed primer ( because you standardized each case with your deluxe pocket reamer tool) makes the round more resistant to a slam fire from the firing pin slamming into it when the bolt closes.

I am not sure of the preferred depth, but mine measure about 8 mils below the head.
Can you explain how primer depth interacts with a floating firing pin?

jcwit
April 24, 2010, 04:22 PM
Have yet to have a misfire caused by how I seat a primer flush or below flush. I've either been lucky for over 45 years or I have dern strong hammer striker springs. I don't even have problems with small rifle in small pistol applications.

Then again maybe I haven't walked through the pasture long enough.

mallc
April 24, 2010, 04:37 PM
Apparently, this is another reloading issue which is far more complex than I understood. All this time I've just been seating to the bottom of the stroke; be it progressive press, or RCBS hand priming tool.

I now realize how lucky I am that I've not been blown - and that I really must learn to worry more about such things!

Scott ;)

GW Staar
April 24, 2010, 09:17 PM
You guys that are priming with hand primers may not need to think so much about primer depth, but those who do progressive reloading for gas operated semi-autos do.

Slam fires, in such semi-autos, are usually primer-caused, in less-than-perfect reloads. They are either caused by high primers, or not fully seated primers. Then there are thin-cupped primers (like some Federals) that can and have caused slam fires, seated flush or even slightly recessed. That means that some assurance is necessary, that you can seat your primers correctly and progressively, for safe reloads.

Head space concerns, when reloading for these rifles is equally critical, but that's another subject. See the Fulton Armory Url below.

My RCBS Pro-2000 has a mechanical stop that is set to seat the primers at the same depth every time. But there's one small problem. The depth of the pocket can vary. That means that they could be "floating" (not bottomed), just right, or crushed. There's two ways to prevent such problems on an RCBS progressive. One way is to prime manually. The other, & the way I do it, is to use the primer pocket uniformer on the Trim Mate, so that every pocket I load is the same depth. Therefore, I find it useful while setting up, and testing the setup, to use the tail of my calipers to check primer depth.

Floating firing pins really have caused problems with primers in gas guns. CCI even makes a special "military" primer to make sure the floating firing pins in military rifles don't make for a bad day at the range or on a hunt. They aren't absolutely necessary, but they probably are a safer choice for M1 Garrands and maybe even M1A's. Important reading from Speer on the subject
(http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm)

And since I've talked about reloading for gas guns, I suggest those who haven't yet, read the following from Fulton Armory (http://www.fulton-armory.com/) That website hides their internal pages, so once you get to the Fulton Armory site, go to their FAQ page, then to the "Reloading for Gas Guns" page.

Not that I agree with Clint McKee that gas guns shouldn't be reloaded (he manufactures them you know, and what manufacturer condones putting reloads in their guns), but his points still provide the clues to why so many gas guns blow up with reloads, and shooters should learn from, or repeat the mistakes of others. I for one feel safer heeding the warnings.

918v
April 25, 2010, 12:37 PM
OK, but what causes a floating diring pin to discharge a primer that is not fully seated vs. one that is fully seated? For example, if one were to seat a primer perfectly flush with the casehead and another slightly deeper. Why would the flush seated primer be more likely to discharge and not the bottomed-out primer. That proposition defies logic. Everyone knows that a primer which is fully seated to the bottom of the primer pocket is more reliable than one which is not. Why would a floating firing pin reverse that?

GW Staar
April 25, 2010, 08:22 PM
Speer explains it as good as anyone, and better than me. Quoting from the first page in the Speer article linked to in my first post: (read the whole thing)

Virtually all U.S. military Service Rifles utilize firing pins that rest freely within the bolt. Referred to as a floating firing pin, it will actually strike the primer lightly when the bolt is closed. This results in a slight dimple in the primer, which is plainly visible if the unfired round is extracted. This isnít a problem with military ammunition because they use primers with thicker cups specifically because of this. However, it can be hazardous with the more sensitive commercial primers. The risk increases with high primers, headspace problems, and poor gun-handling technique. These risks are covered in greater detail elsewhere in this section. Please pay particular attention to the sections about rifle manipulation, sizing and priming.

Now you know why CCI started making "military" style primers to sell to the gas-gun shooting public.

BTW the whole article is in Speer's latest manual.

Everyone knows that a primer which is fully seated to the bottom of the primer pocket is more reliable than one which is not. Why would a floating firing pin reverse that?

Never said that. A floating firing pin doesn't reverse that. Fully seated, yet not crushed, will always be the goal.

918v
April 25, 2010, 10:56 PM
But Speer does not address the mechanics of the floating firing pin vs. the primer position within the primer pocket. Speer addresses primer sensitivity.

In post #20, DaveP alleges that a primer seated below flush with the casehead is less likely to slamfire in a floaring-firing pin system. I'd like to have that explained because I don't understand how.

GW Staar
April 26, 2010, 11:34 AM
But Speer does not address the mechanics of the floating firing pin vs. the primer position within the primer pocket. Speer addresses primer sensitivity.

In post #20, DaveP alleges that a primer seated below flush with the casehead is less likely to slamfire in a floaring-firing pin system. I'd like to have that explained because I don't understand how.

It's simply a matter of reach. Think boxing, except think of the glove traveling against more friction, say in thicker air or even water. Damage caused by the glove is a function of glove speed, and reach. If the glove meets your face at the start of the forward stroke, lack of speed reached will do little damage. When adaquate speed is reached first...major damage. Friction adds to the equation as is moves to the end of the arm's reach, slowing it down slightly, but even more important, the full weight behind the hit doesn't reach the target, so less damage. In the firing pin's case, the firing pin has a stop (its reach). If the primer is too far forward (towards the pin) the pin can drive through the primer (figuratively) with all its weight, unhindered by the firing pin's designed stopping point. The round can slam-fire.

jfdavis58
April 26, 2010, 12:08 PM
Unless you enjoy the tedium of collecting data and running statistical calculations, single seating depths tell you very little. In fact knowing the seating depth from measuring a head to primer distance probably tells you nothing.

Far and away the more important issue (and then likely only for rifles) is the pocket depth AND THAT IT BE SQUARE (shouting on and for a purpose). Safety issues demand that the primer be below flush. Uniformity of ignition says they need to be located at approximately the same below flush dimension plus or minus a very small variation.

With quality pistol brass a complete cleaning of the pocket is usually sufficient to put primers a couple thousandths below flush and allow a solid seating contact between primer and pocket.

Marking the case at several points around the head circumference; measuring the pocket depth at these points; collecting the data and reducing it to some average depth, and maximum depth; then cutting all to this maximum depth (assuming it's still in spec) is the process. Expect to cull some number of cases that cannot be made square in the pocket and still be kept within the nominal (optimal) depth maximum.

Removing more than the measured statistical maximum amount of material is counter productive, i.e. there is no need to go to the pocket depth maximum (unless you know you will use very tall primers--primers don't all have the same height dimension.) Finding good primer dimension data is required as well as finding nominal pocket dimensions.

I doubt the inertia of a firing pin traveling to some distance X is significantly greater than the same pin traveling to X plus 1 or 2 thousandth of an inch; use primers specific to your application (gun) The reasons to seat primers squarely (against a solid surface) is obvious and logical--better uniformity of ignition. Seating primers below flush is obviously a safety issue-primers are sensitive and we don't want to offend them with rough handling (in the box, loading to a magazine of any type or while chambering).

918v
April 26, 2010, 12:15 PM
It's simply a matter of reach...

In the firing pin's case, the firing pin has a stop (its reach). If the primer is too far forward (towards the pin) the pin can drive through the primer (figuratively) with all its weight, unhindered by the firing pin's designed stopping point. The round can slam-fire.

If the firing pin has a "stop" that prevents it from striking a properly seated primer with full force as the bolt closes, how does the hammer overcome that "stop" to discharge the primer?

GW Staar
April 26, 2010, 03:00 PM
If the firing pin has a "stop" that prevents it from striking a properly seated primer with full force as the bolt closes, how does the hammer overcome that "stop" to discharge the primer?

OK, I admit that stop was a stupid word choice, because before M1's and M14's, and M16's for that matter, were given "lighter" firing pins, even properly seated factory rounds were going off when they shouldn't. The M16 just about got canceled until they "fixed" it with lighter firing pins. IMO it must be that the added length of travel, (friction resisting the lighter firing pin) must slow the forward momentum of the lighter firing pin just enough to prevent a slam fire situation, at least with a properly "hard" primer cup, and a light enough firing pin.

Quoting from Speer again:
In semi-autos, this condition becomes downright hazardous. With their higher bolt speed and greater inertia, the chances of a high primer igniting when the bolt drives home is greatly increased. In the case of Service Rifles in particular, high primers are far and away the leading cause of slam-fires. Slam-fires are very rare in serviceable rifles using military ammunition. Handloaded ammunition, unfortunately, is another story. Most slam fires can be traced directly to certain errors in the reloading óand most often, the priming process.

Admittedly, they didn't (or maybe even couldn't) actually explain, beyond any doubt, the actual process of how it happens, but after reading their whole article, it's obvious to me that they've tested this scenario for years. And even if they can't guarantee the exact mechanism, it still happens. I'd rather not load high primers in my rifles to see it they're full of sh..t. You can if you want.

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