Testing CCI 400 primers for slam fire in an AR15

[tangolima]

Unclenick. 30 ounce-inch from 6" drop. Shouldn't the ball weight 5 ounces? Sorry I am more familiar with SI units. Thanks.

-TL

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[hdwhit]

Nick C S wrote:
In conversation with a buddy of mine (via text) a few months back, I mentioned the CCI 400's and he immediately responded with the alleged slam-fire phenomenon and recommended #41's.

Starting 1980 and extending until I went to graduate school (where I couldn't take my loading equipment), I loaded several thousand 223 rounds using CCI primers (400, 450 and BR4) since they were all I could get at the time.

The rounds do not show any noticeable difference in performance based on whether the primer was standard, magnum or bench rest. And I should mention that it wasn't just that I was a poor marksman who couldn't tell the difference, I was on the college rifle team.

I was a new reloader at the time and wasn't near as well-trained nor attentive to what I was doing as I am now. I have gone back and looked at the remnants of those rounds. I see loaded cases that I would today reject on sight.

Speaking of the primers:

• In general, the primer is flush with the case head (not 1-2 one-thousandth below like they should be), but
• Some are actually slightly above the plane of the case head.

That should be the makings of "slam-fire central" yet with 1,600 of those rounds expended, there has never been a:

• Slam-fire,
• Hang-fire,
• Failure to fire,
• Failure to feed,
• Failure to cycle the action, or
• Failure to extract.

The bottom line, is even with poor technique, a penny-pinching college student was still able to load ammunition that has proven been safe and effective for nearly 40 years.

[IMtheNRA]

For what it's worth, I'll toss in my own observations of slamfires and CCI-SR primers in my stock Colt 6920. When shooting my practice / plinking rounds, I get about one slamfire per 2,000 rounds. The offending round is easy to spot on the ground, as the firing pin indentation is tiny and very shallow. These slamfires happen during a string of fire, and I've not yet had one when chambering a round.

For match rounds, I just use the harder CCI Bench Rest primers to keep from getting DQd for a slamfire.

[Metal god]

IMtheNRA , A slam fire once every 2k rounds seems extreme to me . Only because It does seem hard to find anyone that's had an AR slam fire or even seen it happen and yet you are having them every couple thousand rounds . That sounds more like a trigger control issues or dirty bolt issue . I remember when I used my Geissele Hi-Speed National Match trigger for the first time . I was getting doubles often and thought the firearm was slam firing because I only pulled the trigger once . Turns out there's a little sweet spot in there where if you release the trigger slow at just the right timing the hammer will drop again . I don't believe it's actually when the trigger was moving forward that released the trigger , Rather the 1# second stage was being pulled from recoil as my finger SLOOOOWLY passed that stage on reset causing the gun to fire a what felt like when I was releasing the trigger . After learning this could be the problem and a little more concentration on how I work the trigger , It's never done it again .

[HiBC]

I'm speculating.No data or references.

Agreed,there are shades of gray in primer sensitivity. I use #41's when I have them.I don't stop shooting because I don't have them.

As many configurations of AR's as are out there,I wonder how much the velocity of the BCG coming into battery varies? The forward fps of the firing pin?

Rifle vs carbine,various buffers,various springs,parkerized vs hardchrome BCG,
JP lightweight bolt carriers,etc. Hydraulic buffers..

I'd just about bet you will find as much there as in primer differences.
It might be some rifle configurations are more prone to slamfire.

It may be that one slamfire per 2000 rounds has other varibles involved

[Unclenick]

One per 2000 is way out of line with what I've seen, even from the Garand and M1A. For sure, there is a "trigger bounce-fire" phenomenon with those guns in which the shooters shoulder, rebounding from recoil, pushes the whole gun forward and against the trigger finger which fires the second shot. But that produces a full firing pin indentation and not the tiny indent you are finding. There is something wrong here. I think you want the gun completely gauged. I'd at least gauge the firing pin protrusion and the depth of the bolt face recess and the protrusion of the extractor beyond flush with the bolt profile to make sure it doesn't engage too soon in the bolt closing timing. A different bolt might solve it.

[hdwhit]

444 wrote:
The firing pin goes through the cam pin.
The cam pin is in a raceway.
Before the bolt rotates (caused by the cam pin traveling through the raceway), the firing pin is not long enough to reach the primer. When the bolt is locked, the firing pin can then reach the primer. But, because there is no longer forward movement of the bolt at that point in the firing cycle, the firing pin shouldn't move forward at that point ??

Or at least that is what I think he is saying.

By George, I think he's got it!

[JeepHammer]

M16 firing pin has a wider shoulder, the bolt CARRIER holds the firing pin back off the bolt tail/firing pin stop until the bolt is fully locked into place.

The idea came to Stoner from firing pins jamming due to carbon buildup, a common issue with other rotating bolt designs.

The bolt carrier opening for the bolt tail is *Supposed* to pull the firing pin backwards as the bolt unlocks, the firing pin shoulder being larger than the hole for the bolt tail.
This also stops forward movement of the firing pin into firing position until the bolt starts to lock, at which point the forward movement *Should* have stopped, and the only movement should be rotation of the bolt.

The cam pin CAN hang the firing pin a little, and that's usually what dimples the primer when the correct firing pin is used AND correctly fitted, although most don't have the correct pin AND fitting, so you get a serious dimple.

A little champfering of the cam pin hole (and I mean very little) usually stops the dragging issue,
While not worrying about the weight of the pin so much (usually sold for faster lock times), keeping the wider shoulder pin helps a bunch, and making sure you have a bolt/carrier that conforms to reasonable specification stops a lot of the issues.

The issue I see the most of (as a gunsmith) is off specification parts.
Everyone & their idiot friend has an 'Idea' about how to lighten this or 'Improve' that, if you are lucky the changes are neutral...
Cutting weight out of the bolt carrier is popular, reducing firing pin weight is popular, along with shaving down hammers, etc...
Everything has it's costs.

[Metal god]

Jeep , Are you talking about the original M-16 firing pin ? The one that is larger then the firing pins they use now ?

I did a little more research and found that the original fix was to add a spring to the firing pin but ultimately they went with a all around smaller and lighter firing pin

http://www.fulton-armory.com/faqs/AR-FAQs/SlamFire3.htm

As you can see the final design is quite different in shape . I don't believe the final design can do as you say if the original bolt design was kept because the diameter of the firing pin is smaller as well as that first shoulder step is now set back further not allowing it to catch as you describe .

Does this make sense or am I still not understanding what you are saying ?

[edfardos]

two of the last 1000 cci 400s slam fired for me. ar15 cannot fire out of battery, so its just a double tap. the slam fired primer looks different than the rest, with more extrusuion into the firing pin hole. cci 450s work perfectly.

[Marco Califo]

I pierced primers in hottish 223 loads using 400s in a bolt gun and immediately switched to 41s, which I like. Now I use russian 556 which seem equal.
I do not think flirting with disaster is a safe and sound logical test, unless you are tieing your gun to a tree, use a long string to pull the trigger, and can readily afford to replace or repair your gun.

[T. O'Heir]

The brand of primer has nothing to do with slam fires. Slam fires are caused by improperly loaded ammo(usually improperly seated primers), not the primer or the rifle.

[Metal god]

I pierced primers in hottish 223 loads using 400s in a bolt gun and immediately switched to 41s, which I like.

I'm not sure that's the best way to fix an over max pressure load . CCI #400 should be plenty hard enough for bolt guns . If you are piercing primers , It's not the primers that are the problem . The firing pin may protrude further then normal . It could be thinner with a finer point cutting into the primer cup . You could be way over pressure . None of those things are the fault of the primers .

[Marco Califo]

Changing the primers solved the problem I had. Other primers are thicker, and handle higher pressure. I prefer the stronger primers, with heavy bullets and loads near max. That gun shoots fine, and there is nothing wrong with the firing pin. I chose not to use the 400's except for tame 55 gr FMJ loads, and not to buy any more.
Another reason I use #41's, or equivalent, is because I like to use mil-surplus powders like WC844 (aka H335). Magnum primers are recommended for setting off ball powders consistently. #41 are considered to be magnum primers. Current USGI 5.56 M855 is loaded with#41 equivalent (color is different only) primers and WC844.