How important is the .005 primer seating depth??


December 27, 2002, 02:09 AM
I'm almost finished setting up my RCBS pro2000. Here's another problem I ran into with the primer seating.

First of all, here's the components: .45acp S&B brass (also tried some Winchester), Winchester Large Pistol Primers, and I'm assembling on a RCBS pro2000

I made sure to clean out each primer pocket with an RCBS stainless steel primer pocket brush.

I've been trying my best to try to get the primers to sit .005 below flush, and it took me some hard pulling on the lever just to get it to sit flush. I'm pretty scared to try any deeper as I'm already putting quite a bit of force in seating to flush. I don't want to blow a primer. (how easy is it to do that anyway? I feel like I'm putting an excessive amount of force seating the primer)

I also tried the same thing with the Winchester brass. I've heard about how tight S&B primer pockets could be. I'm having the same problem there too, but not nearly as pronounced. I measured the depth of both primer pockets and they come out to the same. I also measure the height of the primers and they're quite a bit shorter. I don't see why it would be so hard to go deeper if I've already seated that far.

Anything wrong with just seating to flush, or should I really go for that .005?? If there's any recommendations/advice, I would greatly appreciate it. Thanks all.

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December 27, 2002, 02:30 AM
is the brass once-fired, or new? i have no experience w/ s&b brass. i did have a batch of winchester brass some time ago that i couldn't get the primers to even make it to flush. at the time, i was new to reloading...i looked at it and said to my brother, "hmm...lookit that." he said, "hmm...let's go shoot."

anyway, not knowing any better, we went out and shot. had a helluva time getting the bolt to close on a couple of those rounds, but we did. and they shot. nothing blew up...perhaps they weren't the most accurate loads i ever assembled, but they did shoot, and on the second loading of that brass, the primer seated perfectly...

i guess that that is a long-winded way of saying don't worry too much about it.

December 27, 2002, 02:35 AM
You do have to use a fair amount of pressure. In 20 years of seating primers manually I've never had a primer go off, though it is possible. I wouldn't be too worried about measuring each primer to make sure of the seating depth. I usually just run my finger over about every 5th one to make sure. You can feel if it is below the edge. If the primer isn't seated solidly against the bottom of the primer hole then the force of the firing pin will be taken up by the forward movement of the primer and it may not go off. The anvil must be seated firmly to the bottom of the hole.
Hope this helps.

December 27, 2002, 02:42 AM
Both S&B and Winchester brass was once fired. So you think it'll just loosen up in time??

Bushrat, with the amount of pressure I'm pushing on this lever arm, I don't know if a firing pin alone could push the primer any further.

I'm also contemplating seating by feel, but being a newbie to reloading, I don't know if I'm ready for that. I also don't know if I'll be able to feel that well through a progressive lever arm.

December 27, 2002, 02:48 AM
if they've already been fired once, they should be loose enough to fit a primer into. how clean is the primer hole? have you tried a different brand of primer?

December 27, 2002, 02:55 AM
dakotasin, the primer hole is pretty darn clean. I really scrubbed both of them out with an RCBS tool to make sure there wasn't anything getting in the way.

I haven't tried any other primer. I'll probably stop by the local shop to pick up a small pack of feds, rems, and cci.

Flash Hole
December 27, 2002, 09:10 AM
The press maybe the problem if it is new. Check everything and give anuther try.Primers may be hard to get started into the pocket but should go easy after you get them started.

December 27, 2002, 09:29 AM
I load on a Dillon 650 and I sometimes have a primer that fails to bottom out in the primer pocket. It sometimes takes a considerable pressure on the handle to get the primer to go below flush with the case head, and although I guess it is possible to have a primer detonate I have never heard anyone say it happened to them. Probably the worst that can happen is that a revolver cylinder may not rotate or a semi auto may not strike the primer with enough force to both finish seating the primer and igniting it as well. As long as this occurs during a practice session, no harm, no foul, and I would never advocate the use of reloads for personal protection for a variety of reasons.

Jim Watson
December 27, 2002, 09:53 AM
There is no magic to .005" but for safety and good ignition, the primer must be at least flush. High primers are a major cause of misfires; I have never seen a slamfire on one and don't want to.

I have no experience with a RCBS-2000, but my Dillon SDB had one requirement on primer seating in .45 ACP - as hard as I could push while grasping the press frame in the other hand. It was not that the primer post did not travel far enough, I used a rifle primer pocket uniformer on some and primers seated just about out of sight. It was that the primer pockets were tight and the press had very little leverage at the end of the stroke where it seated the primer. Writers go on and on about "feeling" the primer seat. Well, you can't feel much if you are pushing as hard as you can. I have little trouble seating primers with one thumb in a Lee hand tool. Both thumbs if it is a tight pocket. My Dillon S1050 seats primers on the downstroke. They are all the way in, all the time.

I recommend you:
1. Call RCBS, just to be sure you have exhausted all machine options.
2. Lean on that handle. I have never ever popped a primer in any reloading tool. But I have never slammed or hit the handle, either. Slow pressure will crush a primer but not fire it.
3. A primer pocket uniformer will fix each case, but it is a tremendous amount of work to go to on an automatic pistol round that you will likely lose before it wears out.

December 27, 2002, 10:43 PM
Quick post skim & what I do is seat primers to their best depth.

Primers themselves have their own thickness tolerance, so does any brass pocket.

Add up all the variables & it cold drive you crazy from the git-go.

Without reaming pockets to depth, you have no "zero" starting depth + the primers themselves vary.

Since you're measuring "depth" from the brass case head, all your measurements are suspect from the beginning.

Just seat them to seat well & good & you will be set to go.

One can get lost in the details that don't matter, or even exist in the first place.

December 24, 2006, 09:16 AM
I have loaded over 10,000 cases over the yearrs and the problem you are seeing with not being able to close the bolt is not related to the primer, but with a distorted case. As you are seating the bullet, sometimes the bullet will drag going into the case, this causes the brass case to be pushed downward. This will bow the case out slightly. Sometimes it is noticable, other times it is not. Also, if you are using crimp style cases, like the 9mm, .223, etc for semi automatics, you might have the die set down too far where it crimps the case, but isnt finished seating the bullet yet. This will distort the case. Thought I would pass this along.....

December 24, 2006, 10:26 AM
As long as the primer is seated at least flush it will not affect funtion of the firearm. If the primer is not seated all the way to the bottom of the primer pocket it can cause misfires as part of the energy from the blow of the fireing pin is wasted seating the primer the rest of the way. The primer can be hard against crud in the bottom of the primer pocket and still go bang, it just can't have "space" to travel before bottoming out. :)

The Bushmaster
December 24, 2006, 11:19 AM
If you are not getting the primer at least flush with the case head. Look for another problem other then a primer pocket problem. If the primer pocket is clean, as you mentioned in your first post, then you have something else wrong like a primer seater stem that is not adjusted correctly. As far as measuring the depth of the primer below the case head. Waste of time. If you are in doubt, run your finger over the case head. You will be able to feel if the primer is seated or not. Your finger will be able to sense whether the primer is above, flush or below the case head (preferably below the case head).

Let us know what you find...:)

Jim Watson
December 24, 2006, 11:43 AM
You reckon he is still watching this thread after four years? I hope he has it straightened out by now.

Bad Flynch
December 24, 2006, 12:43 PM
IIRC. the SAAMI spec. for primer seating depth is 0.002"-0.005" below flush and most handloaders do not measure it. In fact, many benchresters measure the compression of the primer pellet after the anvil hits the bottom of the primer pocket.

The quality indicator here is that the primer be below the case head and reachable, all tolerances stacked, by the firing pin. RCBS makes, or did make, a Go/No-Go type primer gauge so that one might set his machine up. I have used it over the years on long production runs, but it requires that one measure a fair number of cases so that the maximum and minimum can be determined for that lot of brass (another good reason to stick within one brand and one lot of brass for a given batch of ammo).

A reloader, bent on absolute uniformity, could ream all of the primer pockets to a consistent depth, too, but what a PITA that is. Some benchresters will also segregate primers by anvil height groups: not a pleasant thought for a long run of ammo, either.

Simply clean your primer pockets by depriming before vibrator cleaning and then clean in ceramic media that will get into the primer pockets. If your are fussy, you could cull the ammo with high primers and use it for fouling shots, and so on.

The Bushmaster
December 24, 2006, 01:14 PM
Now how in he++ did we miss that, Jim?:confused: :rolleyes: :banghead: :D

December 24, 2006, 10:49 PM
Very important. If it's even .001 inches off either way, floods will ravage Africa and locusts will destroy millions of acres of crops. Be very careful when you seat a primer. You don't want to be responsible for the deaths of millions, do you?

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