The #41 primer refers to a military specification. There are those who deny that there is such a thing as a mil spec primer, but clearly there is. This is the top drawing for the military #41 primer:
This is the top drawing for the #34 military primer, which is a large rifle primer.
The military used to make weapons and ammunition and knew enough to tailor the ammunition to the weapon. Military weapons tend to have heavy firing pins and robust ignition systems. Heavy, free floating firing pins required less sensitive primers, or the slamfire rate would be unacceptable. I am of the opinion the original military primer specifications required the use of a specific priming compound and primer materials, such as cup thickness, cup hardness, anvil angle, and anvil material. The bridge distance was probably specified. Of course there would be a sensitivity requirement for the primer.
Incidentally, there are a lot of military primers and military priming compositions, this table shows primer mixes:
I am of the opinion that the product specifications that required specific materials and compositions have been relaxed to performance specifications. That is, the primer has to meet sensitivity specifications, temperature requirements, ignition requirements, and interface requirements. That would allow Federal, for example, to make a "mil spec" primer using their own primer compound. As long as the Federal primer worked with all the powders, rifles, machine guns, in all environmental conditions, their primer would be acceptable.
Any contractor who makes ammunition for the US Army makes "mil spec" ammunition. In 1999 (or so) CCI decided to make its military primer product line available to the public. Till then, all that was available were the more sensitive commercial primers. Civilian firearms are horribly maintained, hardly anyone changes mainsprings, or any springs, Civilians maintain their firearms about the same they maintain their vehicles.
Given the weak, marginal ignitions systems found on most Civilian firearms,
IT DON’T GO BANG: FIRES, HANGFIRES, MISFIRES AND SHORT ORDER COOKS IN JERSEY http://gunhub.com/ammunition/42928-don-t-go-bang-fires-hangfires-misfires-short-order.html the deterioration of mainsprings only cause ammunition companies headaches as civilians with antique blunder busses blame the ammunition for not going bang, not their ill maintained antique ignition systems. This causes a race to the bottom as ammunition companies have an financial incentive to make the most sensitive primers possible, to eliminate customer complaints about their ammunition. This was all fine as long as civilians only had revolvers and bolt guns, but when military automatic rifles appeared in vast numbers, the frequency of slamfire incidents and reports increased to become a noticeable problem. Before the internet the only allowed causes of slamfires were
"your high primer and your worn out gun",* but shooters were having slamfires with factory ammunition in new guns, so enough started realizing that there was something more was behind their malfunction. It turns out overly sensitive primers are the main cause of slamfires, not shooter negligence. Besides CCI, Federal was the other company to sell "mil spec" small rifle primers, but I have never one a box anywhere, so I don't know what happened to them. But this is the ad roll out and some commentary on Federal mil spec primers:
http://bulletin.accurateshooter.com/2011/09/new-federal-gold-medal-match-primers-for-ars/
September 11th, 2011
New Federal Gold Medal Match Primers for ARs
Federal Ammunition has released a new type of small rifle match primer optimized for AR15s and similar semi-automatic rifles. The new Gold Medal® AR Match Primers, designated GM205MAR, have harder primer cups than the popular Federal 205M match primers. The harder cup is designed to perform better in semi-automatic actions that use free-floating firing pins. A Federal spokesman said that Federal’s “normal” 205M primers were not ideal for use in firearms, such as ARs, with free floating firing pins. Hence Federal designed the new GM205MAR primers. These are available now from major vendors such as Midsouth Shooters Supply, which offers the new GM205MAR primers for $35.22 per thousand.
Here's the skinny on the Federal GM205MAR primer.
http://68forums.com/forums/showthread.php?32572-Here-s-the-skinny-on-the-Federal-GM205MAR-primer
My friend at RCBS contacted the expert at Federal, and this is what he was told:
Mix is the same as in the standard small rifle primer. The primer cup is thicker, as is the anvil. The thicker cup and anvil “should” desensitize the primer a bit, and “lessen” the chance of a slam-fire. Federal primers are in general, more sensitive than CCI and less tolerant of firing pin blows during loading into the chambers of the M1 Garand, M1-A, and AR platforms.
I hope this helps shed some light.
* This was a lie by the US Army and its supporters in the National Rifle Association. Post WW2 the only semi auto rifle in Civilian hands in any sort of quantity was the M1 Rifle, and that basically in the hands of Highpower Competitors. In the early 60's you could get a Garand from the US Army if you physically went to the National Matches and bought a NM Garand. Sufficient numbers got into the hands of Civilians who followed their bolt gun reloading practices of neck sizing, partial neck sizing, and the use of sensitive commercial primers. Since competitive shooters fire thousands to tens of thousands of rounds, it was only a matter of time that out of battery slamfire reports started to surface in the shooting community. The Army and it mouthpiece, the NRA , would not admit that the issue US Service rifle and its derivatives had a design fault. This mechanism not only can slamfire in battery, it can slamfire out of battery! Both created and disseminated the story that slamfires and particularly out of battery slamfires, were only caused by worn out guns and bad reloads. This shifted all problems onto shooter negligence which of course, suited the Army as it did not have to acknowledge this problem, and it suited the NRA because Garands, M14's, and M1a's, were the only service rifles allowed in NRA competition.
