Activate primers


Started reading Bussard’s Ammo Encyclopedia and there is a short section on primers. It is stated that the boxer primer that I buy for reloading is not activated until I press it into the primer pocket and this moves the anvil close enough to be hit and go off. If this is the case you could throw them on the ground and they would not go off. In other words quite safe. Is this correct? Vic


In my humble opinion, based on 25 years of reloading experience, that information is completely incorrect.




While I don’t want to stray too far into the reloading aspect of your question, a couple of thoughts on how I think maybe the facts got a little distorted somewhere in the mix.

Seating of a boxer primer firmly in the primer pocket with the anvil butted against the case web is important as otherwise the energy of the firing pin’s forward motion can be transmitted into moving the whole primer rather than crushing the primer composition between the cup and anvil. Failure to seat the primer firmly can result in a misfire.

Of the thousands of primers I’ve handled, a few have been dropped…Never has one detonated. I believe the mass of the primer is just too small for the impact to make it happen with gravity alone.

So…seating a primer firmly makes for good detonation and unseated primers don’t tend to detonate when dropped. Perhaps the blending of these facts led to the assumption you found in that text.




I don’t know Mr. Bussard and have not read his book but it may be that he is referring to one of the shooting myths that seems to pop up every few years. That is, that seating a primer deeper than normal, applying pressure to the pellet, will tend to make the primer more sensitive, resulting in more uniform ignition and accuracy.

Benchrest shooters have tried and tested every conceivable gimmik to shrink their group sizes, and doing strange things with primers is no exception. None of them make any difference. Believe me, if they did, it would not take long for the word to get around and everyone would be doing it.

Modern small arms primers and primer pockets are sized so that a primer seated with the anvil touching the bottom of the pocket is all that is necessary to ensure proper ignition. Most benchrest and other competition shooters will ream primer pockets to ensure their uniformaity and will use hand held priming tools so they can feel the primer being seated but that’s as far as the majority will go.

I can’t speak for the older mercuric/corrosive or the new “green” primers. Maybe they did/do require special treatment but if they did, I doubt if the mere act of seating would “activate” them.




I would concur with the previous posts. the word activated is misleading. The primer is not capable of functioning as a primer until the anvil is in contact with the body of the cartridge. At that point in time it (the anvil) becomes immobile. Up to that time it cannot provide the resistance required to squeeze the priming compound against the hammer strike and create the necessary friction.

Rather than say activated I would perhaps use the word enabled.

What it does say , however obliquely is that free priimers are much less capable of accidental detonation from mishap or accident although not entirely so. In recent years regulations concerning the packaging of primers has sought to isolate individual primers in plastic trays where a lot of free space exists between the primers. I have always though this, although well intentioned, is largely unnecessary. I am unaware of any instances where bulk primers have spontaniously detonated.


Primers, anvil; position, “sensitization” and mass explosion.

Firstly, The Anvil: it has to be firmly seated into the base of the primer pocket to act as a resistance to the Firing Pin strike.
(That is why a Berdan primer is more reliable, it has a solid, case based anvil).

For safety in manufacture, the anvil is only pressed into the primer cup sufficiently for it to remain in place under the stress of loading/seating, but not sufficiently to ignite the primer. In Seating the primer, the seating depth is calibrated to set the anvil against both the base of the Primer pocket, AND bring the tip of the anvil in contact (but not pressing into, the priming compound ( usually the Priming compopund is dished in the middle, when pressed into the cup at manufacture, so as to “surround” the tip of the anvil, to allow for "Off-centre strikes).

This procedure is known as “senstization” of the primer, and can be tested by Primer strike measurement devices (used Forensically and in Primer Factories, to test primer sensitivity, both as a loose primer, and as a seated primer. Factors affecting sensitivity are the chemical compound sensitivity to impact, the thickness and hardness of the cup and anvil, and the position of the anvil vis-a-vis the priming compound,
SO the depth of seating is of importance, both for Boxer and Berdan primers…“over seating” can cause a discharge, usually seen in Berdan primers (about 10 in my 35 year experience of handloading…that is why a “postive seating stop” is essential for Berdan primer seating. Over seating in a Boxer primer usuall;y leads to deformation of the (thiner) anvil, with out detonation, usually only erratic ignition due to a cracked pellet of priming compound. (One or two Boxer “let-offs” in 35 years.)

Bulk or mass explosions. Can and DO occur if the primers (Boxer) are carried loose /in Bulk.
1909 or 1908, a US Factory (can’t recal which) was loading Military .30USG ( krag) ammo, and Blew up, killing several dozen workers (mostly women). The cause was ascertained later at inquest, that the Primer “Reloader” who fed the priming machines, would walk through the Loading area with a Steel Bucket of Boxer primers, jangling them as he went to create a musical tune…he was well known for this trait…and surviving workers noted that all of a sudden, he just disapeared in a great flash…and all the other Powder in the place followed suit, destroying the building, killing the workers, and the worker concerned was never found…the remains of the bucket were, completely opened out into an almost flat sheet of steel, and peppered by primer cups.

After that incident, it became mandatoruy in the USA for all primers to be transferred in trays. made of Wood or papermache’…Later on (Frost, the Making of Ammunition, NRA Publ.)mentions that two Winchester Western employees in the early 20s, patented a 500 primer tray made of Cardboard, with paper baffles, and sockets, to transfer safely and deposit 500 primers at a time “In House” from primer manufacture store to Loading Room, and deposit them into the primer Loading tray with the minimum of motion…primers shed Primer “dust” which is highly explosive, so cleaning up the machinery is also done on a regular time frame (Several times a day.)

When I visited S&B in 1993, their Primer transfer trays held up to 200 primers or so , as did their feed trays.

The design of Commercial (100 or 250 primer tray packs ( Europeans tend to the 250 pack (ie, RWS) in Plastic, with either Pockets (US) or rails(European) are designed to prevent the compression of the anvils into the cups by an impact, to separate the primers sufficiently to prevent contact sympathethic detonation;
Berdan primers used to be packed in tinlets (UK) or Flat cardboard trays (RWS) without separation, but as there was no anvil, the “crush factor” is less of a problem…of course, enough impact will set off Berdan Primers as well and, if the primers are all oriented one way (some makers, not all) to aid in filling your priming tray or feeding your primer tubes, with-out further primer shaking.

Primer Chemistry and Mechanics is a precise and interesting are of Knowledge.

Doc AV
AV Ballistics.