There is a lot of evidence out there that says differently.
Sunray actually knows better about mil spec primers, for at least a decade he and a trio of other CCI haters have been disparaging CCI, CCI primers at another forum. Initially CCI was the only US manufacturer offering its mil spec primer line to the market and these guys denied slamfires happened, denied there was anything different about mil spec primers, and generally spread hate towards CCI. There is basically nothing I have said about primers that I have not posted in threads where he claims mil spec primers are a marketing gimmick.
This mechanism relies primarily on primer insensitivity to prevent an in battery or out of battery slamfire. Notice in the following photographs that the Garand type mechanism, which the M1 carbine uses, does not have a positive mechanical means of holding the firing pin back, instead the firing pin is entirely free floating through out most of its travel. There is contact with the firing pin retraction cam, but this is not positive nor does it completely retract the firing pin. This cam is there to break the firing pin out of the primer indent, if this did not happen the firing pin would likely break as the bolt rotates out of battery.
Bolt fully retracted
Firing pin just at retraction cam.
Firing Pin fully forward.
Bolt movement is not perfectly smooth. Slow motion pictures on the M14 mechanism reveal a lot of hesitations, vibrations, going on during bolt closure. Bolt bounce exists on other mechanisms, probably exists with this mechanism. Since there is virtually nothing preventing the firing pin from touching the primer during feed, and during the period when the lugs are not in engagement, it is prudent to use the least sensitive primers you can in these mechanisms.
Whenever a firing pin rebounds off a primer there exists the chance of ignition. This is due to the fact that the energy to ignite a primer varies considerable within a lot. Primers can be made to be more or less sensitive, and if you think about it, what can be done is rather obvious. Firstly, the primer mix can be adjusted to make primer cake more or less sensitive. Primer cups can be made thicker, or harder. Anvil angle can be adjusted to be stiff or somewhat “cushion” the blow.
I don’t know if the #41 primer is the proper primer for a M1 Carbine. In the old primer spec Mil-P-46610E “
Primers, Percussion for Small Arms Ammunition” the M1 carbine primer is the least sensitive primer out of all military primers, including the later #41 primer. This was because the M1 Carbine was the first of its kind and the primers could be made very insensitive as there were no other mechanisms using the same cartridge.
A history lesson of a sort, the early M1 Garand had a round firing pin exactly like the M1 carbine firing pin. These are pictures of the rare early round firing pins, when Orion 7 had them, they sold out their inventory at $100.00 apiece!
Obviously the Army experienced slamfires in early Garands because the later firing pin was scalloped to reduce weight. On top is the Garand firing pin, the middle the M14, and the bottom a M1 Carbine firing pin.
Making the primer insensitive for the Garand would have likely caused misfires in other mechanisms which used the 30-06 cartridge. The simplest solution was to reduce the kinetic impact energy of the Garand firing pin by reducing its weight. This was not necessary for the M1 carbine, so they kept the relatively simple to make but heavy, round firing pin. To accommodate this heavy firing pin, the M1 carbine primer spec is the least sensitive of all military primers.
The history of the #41 primer is different and came about due to slamfires in the early M16’s.
http://www.dtic.mil/dtic/
Report of the M16 Rifle Review Panel. Volume 5, Appendix 4. Ammunition Development Program
Primer Sensitivity
Initial Specifications. Ammunition specifications established by the Air Force on 24 January 1963 provided for quality control against cocked, inverted, loose, and nicked primers. The specifications further provided for inspection and test of waterproofing and the crimp of primers. However, the specifications did not provide for specific limitations on primer sensitivity for 5.56mm ammunition.-
Development. At the first meeting of the Technical Coordinating Committee on 26 March 1963,16 / the Air Force representatives submitted a list of reported ammunition deficiencies, which included "high primers" and "primers too sensitive". It was agreed that Frankford Arsenal would investigate the matter and recommend corrective action.
One of the malfunctions reported by the Air Force was the premature firing of cartridges that occurred upon initial charging of the M16 rifle with a cartridge from the magazine, or upon singleloading of a cartridge directly into the chamber, or when two rounds were fired at one trigger pull during semiautomatic fire.
This malfunction was attributed to "high" or protruding primers, although the tests did not confirm this theory..
However, analysis indicates that if high primers caused the premature firing, the firing should have occurred upon impact of the bolt face with the protruding primer. At this point in the weapon cycle, the bolt head would not. have been rotated to the locked position by action of the cam pin and carrier. Had firing occurred with the bolt in the unlocked position, it would have resulted in a blow back and would not have been undetected. No such disruptions were reported-. Since premature firing occurred after bolt-locking, it must have coincided in time with the impact of the bolt carrier against the bolt head. At the instant of impact, the "free floating" firing pin is moving at the velocity of the bolt carrier. The kinetic energy of the pin must be dissipated by such frictional forces as it encounters in the forward movement, and, finally, in impact of the firing pin tip with the primer of the chambered cartridge. This premise was confirmed by the visible indentation appearing on cartridges which were chambered by the mechanism and extracted unfired.
Frankford Arsenal identified test procedures for measuring firing pin energy and recommended limits for primer sensitivity.
Remington Arms Company, on the basis of the information contained in the Frankford Arsenal First Memo Report, undertook the design of a new primer that would be less sensitive and less susceptible to the inadvertent energy delivered to the primer by the free-floating firing pin of the AR15 rifle. Since it is difficult to adjust primer sensitivity by chemical changes, Remington elected to accomplish the desensitization" by increasing the mechanical strength of the brass primer cup, which must be indented by the firing pin to cause ignition.
As a result of the decision of the Commanding General, USAIIC, to modify the rifle, Colt's Inc. developed two designs, a linear spring device and a cam pin friction device, to reduce firing pin energy on bolt closure. These two designs were tested by the Air Force conclusions of this test were that both devices effectively reduced firing pin energy; however, the Air Force recommended against their adoption because they increased the probability of a misfire (although no failures to fire were identified in the test results), added to the cost of the weapon, and adversely affected its reliability. Army tests of these devices indicated that the linear - ~spring friction device was a satisfactory solution; however, at the Technical Coordinating Committee meeting of 10 December 1963, at which a comparison of all tests done by the Army, Air Force, and Colt's Inc. was made, the committee agreed to adopt a modified lighter firing pin, which was used in the cam friction device and was recommended by Colt's as a solution to the problem..
So, to reduce slamfire rates in the M16 the Army did two things: 1) it reduced firing pin weight, and 2) required the use of less sensitive primer, the #41 primer.
The heavy original M16 firing pin on top.
All ammunition makers in the US make “mil spec” primers for US military contracts. To date, only Federal and CCI offer their military product line to the public. All primer manufacturers should be encouraged to do so. Wideners’ sold Wolf primers, part # KVB223M, as an military small rifle primer.
https://www.wideners.com/itemdetail.cfm?item_id=8975 Good luck on finding any of them.
http://bulletin.accurateshooter.com/2011/09/new-federal-gold-medal-match-primers-for-ars/
CCi
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.
Slamfire risks are real, this is a picture of the after effects of an out of battery slamfire in an M1a.
As an idea of slamfire rate, I only have this data, which is on the M14. I have a paper copy of this report. The Army was testing production models of H&R’s and using SA M14’s as control specimens. Six rifles were under test, three by HRA and three by SA. All rifles were gaged for dimensional part compliance, and part interchangeability. Such things as the thickness of the chrome coatings were measured, etc. After gauging the rifles were reassembled and underwent endurance testing which was each rifle was to fire 6000 rounds. The total amount of 7.62 Nato to be fired would have been 36,000 rounds.
USATECOM Project No 8F-3002-04, Comparison Test of rifles, 7.62 MM, M14 Manufactured by Springfield Armory and Harrington and Richardson Arms Company. Author G. E. Hendricks, July 1963.
At round 5271 a Springfield Armory M14 went off out of battery. The report states:
“One rifle fired when the bolt was in the unlocked position causing breakage for the firing pin, extractor, bolt roller, ejector, and stock. The magazine split, causing the magazine floor-plate spring and 12 rounds of ammunition to be ejected against the bench rest from which the rifle was being fired. The case ruptured and several pieces of brass were found in the area. A broken part of piece of brass perforated a cardboard box with was position between the gunner and the proof director. The cardboard box was used as a brass catcher. Not all the broken pieces were found. Although no one was physically injured this is a seriously unsafe condition.”
So, six rifles were tested, five completed the test firing 6000 rounds each, one slamfired out of battery at round 5271, for a total round count of 35, 271. Therefore a crude estimate for the probability of an out of battery slamfire, with mil spec primers, is 1:35,000. You can expect that with less sensitive commercial primers, the out of battery slamfire risk would be higher, by what, who knows?
Springfield Armory warns about the increased chance of a slamfire with commercial primers in every manual sent out with a M1a:
Springfield Armory M1A Manual, page 4
www.springfield-armory.com/download.php?asset=M1AManual.pdf
Ammunition
The M1A is designed and built to specifications to shoot standard factory military 7.62 NATO ammunition. The specifications for standard military ammunition include harder primers to withstand the slight indentation from the firing pin when the bolt chambers a cartridge. This slight indentation is normal. The use of civilian ammunition with more sensitive primers or hand loads with commercial primers and/or improperly seated primers increase the risk of primer detonation when the bolt slams forward. This unexpected "slam fire" can occur even if the trigger is not being pulled and if the safety is on. Use of military specification ammunition will help avoid this.
Every shooter should use extreme caution when loading this or any other firearm. See page 17 for instructions on proper loading to help avoid a "slam fire". Also see enclosed article on “Slam Fire” written by Wayne Faatz
I recommend using the least sensitive primers in this mechanism, and regardless of the primer you use, never assume the gun won’t slamfire in battery, or out of battery. Don’t chamber a round with the muzzle every pointing at something you don’t want to put a hole in!
You can find a number of out of battery slamfire reports on the M1 carbine, you just have to search.
Out of battery Slamfire in M1 Carbine with Federal American Eagle Ammunition.
http://www.thegunzone.com/ij-m1carbine_kb.html#nb2
I first found The Gun Zone while researching my new Glock 21. Yes, I am a Glock Fanatic, but I have to say that I do appreciate this site and I like to see that all points are covered. Nothing is perfect. End of story. To say otherwise is at best hyperbole. I'm still a Glock fanatic because I've had nothing but outstanding results with them. I'm also a 1911 Fanatic, and a S&W revolver fanatic1. I'm also a guy who like to have every scrap of information I can. Thank you for providing the other point of view.
Above are some photos of an Iver-Johnson M1 Carbine that self-destructed while my wife was shooting it. As kB!s go it was pretty mild. However I think there should be some kind of warning out there about these old carbines. Every one of them I've picked up will fire with a partially open bolt. This is not a problem until they get dirty or use bad ammo. On this day we were using brand new Federal American Eagle FMJ rounds. The bolt failed to close all the way and, well, kB!.
We had been having a nice family outing at the range. A friend, the actual owner of the carbine, brought along a few guns for my wife to try out to find something with which she could plink.
We had fired about 75 rounds from the carbine prior to my wife trying it. On her third round the gun emitted a small blast from the breech and blew a chunk of the stock off the right side. My wife and I got our faces full of assorted crap flying out of the gun, and received a few minor burns. Luckily no one was seriously hurt.
The bolt was blown apart and the stock split along the operating rod. I recovered as many parts as I could locate and packed up for the day.
I do not know the DOB of the Iver-Johnson other than it's a "50th Anniversary (1941-1991)" reproduction, so I'm going to guess it's probably very late '80s, early '90s.
The ammunition was American Eagle. No surprise there I'm sure. The rifle, remaining ammunition, and spent casings were sent to Federal for testing. Federal came to the conclusion that the failure was due to a malfunction of the Iver-Johnson2. The rifle did not close properly prior to the ignition of the cartridge. The casing showed no signs of an overpressure load.
After receiving the carbine back I was able to repair part of the damage with a new bolt, but I had trouble finding a replacement stock.
Even with the new bolt the carbine would still fire prior to full lockup. I've seen more than one M1 Carbine lately that will do that.
Iver-Johnson's demise prior to this incident left me with no ability to obtain comment from them.
The pictures are from two days after the event and show the damage to the gun from various angles. The owner took them prior to sending the carbine to Federal as a "CYA" measure.
The other photo shows the case that failed, a fired case from the same box, and an unfired cartridge, also from the same box.
http://thefiringline.com/forums/showthread.php?t=455111
Witnessed 'powder burn' at the range today
Yikes. Gentleman was renting an M1 carbine from the range store and the 15th round of PMC blew off the base sending unburned powder into his face. He came into the store a bloody mess.
Fortunately he was wearing safety glasses and the 'freckles' were just superficial. Scary to witness though.
They figured the gun fired out of battery somehow. We saw the case head and it had broken off about 3/8".
Sunray knows all of this, and this is the most distasteful part of reading his posts: what sort of mind could knowingly give advice which will hurt or cause injury to another person?