• If you are being asked to change your password, and unsure how to do it, follow these instructions. Click here

Primer Question

Where did you find the info? I've always wondered, but will keep for future use.
The site is on the top of the pic I posted up from the screen shot I did. Brian Enos Forums.

That's great info about the cup thickness and what is recommended/not for AR's and nice to have all in one place.
 
It's also caused by the primer moving under it's own weight, which is why it's called a slam fire. Military rounds also have a tar like substance to stop primer movement, as well as a crimp. Many think the tar is a sealant, which it is, but it's also a glue.
I discovered this working at ADI, where they were making 20mm cannon shells.
Wish I still had access to that powder!

Cheers.


Cheers.
Thanks, I learned something today. Never to old to learn.
 
@Veteran.
No, 41's aren't different in how they seat, they are less sensitive with a harder cup.
All primers are designed to be seated below flush with the case head and have the anvil and cup crushed until they are flush with each other. This crush also pre-compresses the priming pellet slightly, which is a design feature. It needs this so that the pellet gets all of the firing pin energy.
Different primer brands require different crush. Some only require .003" crush once the primer hits the bottom of the pocket, others .004" and military can be as much as .008".
Federal primers are sensitive to crush amount, Winchester not so much.

Cheers.
Magnum,
How much crush do you recommend for Federal primers?
 
Primer hight doesn't cause Slam fires ( they could only if seated improperly) Slam fires are caused by the firing pin rebounding.
I was surprised to learn that some (many?) rifles do not have a spring to hold back the firing pin until it is struck by the hammer (like in a 1911).
I learned this when I had my SKS trigger upgraded. The upgrade included a spring for the firing pin, absent from the factory. Then I started building ARs -- no spring. Seems like asking for a discharge when dropped. Can someone expand on the pros & cons of springs here?
 
I was surprised to learn that some (many?) rifles do not have a spring to hold back the firing pin until it is struck by the hammer (like in a 1911).
I learned this when I had my SKS trigger upgraded. The upgrade included a spring for the firing pin, absent from the factory. Then I started building ARs -- no spring. Seems like asking for a discharge when dropped. Can someone expand on the pros & cons of springs here?
Tagging in to hear some feedback on this.
 
I was surprised to learn that some (many?) rifles do not have a spring to hold back the firing pin until it is struck by the hammer (like in a 1911).
I learned this when I had my SKS trigger upgraded. The upgrade included a spring for the firing pin, absent from the factory. Then I started building ARs -- no spring. Seems like asking for a discharge when dropped. Can someone expand on the pros & cons of springs here?
The pin itself doesn't weigh hardly anything (original spec is titanium I believe?), it can't ignite a primer with only it's own momentum. At least a correctly spec'd and seated one. It will dimple a primer, but that's proof that it can't light one off because it for sure hits them.

I'm sure there are exactly 1,397 "what-if's" that could all result in slam fires, but a correctly maintained pin in a correctly maintained carrier in a correctly maintained rifle with correctly specified ammunition... see the trend there?
 
Last edited:
Correct. Do not EVER place a round in the chamber and release the bolt. You will have a slam fire. Always from the magazine. ALWAYS.
Ok, apparently I underestimated the power of human.... intelligence 🤣 I guess that's a fair what if.

Are you saying in an SKS or an AR? It would be a trick to single load a round in an AR.
 
The AR. It's not that difficult, just tilt the muzzle down and flop one in. Now admittedly few folks would ever do that but it will cause problems due to an increased carrier velocity. Try it with a dummy round.

It was just a public info advert. 😁🤯
 
Here are some primer & target photos.

IMG_1549.JPG

IMG_1551.JPG


The first image is a shot of a CCI 450 (left) and a CCI 41 right. The CCI450 is nickel plate and the CCI 41 brass. There appears to be tiny bit less anvil protrusion on the CCI 41 (brass) than the CCI 450. I have not actually measured the anvil protrusion but plan to do so with a small bunch of primers. I would be surprised to see any variations more than .002 with most less than .001.

The CCI 41 is my goto small rifle primer and I use them in : .20 Practical, .204R, .223, & 6.5X47 Lapua & have plans to use them with a 6mm CM & 6.5 CM that are in the process of being built.

The target shown is a 300 yard group shot with my 11 twist .20P rodent rifle with 40 VMax's, LC 5.56 brass & IMR 8208. I have no plans to discontinue using 41's and hearing other shooters reject them does not cause concern - been using them for years. Big piles of dead rodents of all species - up to 400 plus yards. Some target competitor shooters use 41's in 6.5X47's. Went .1 mrad left after 2 shots on right side & paid attention to detail.

On the slam fire stuff - I never drop a loaded round into a chamber & let the bolt slam home. I have never fired the NRA HI Power course with a .223/5.56 but understand that fast twist AR .223's are used with 77 grain bullets at 600 having rounds that are too long to fit inside a magazine. Is there some type of a "sled"(old past Garand shooter) that will allow single loaded 77 grain bullet round to be safely chambered?

edit: found a sled (Bobsled!) for my AR so I won't waste lots of bullets & can shoot 75 ELDM's way out there. Cost about $50, looks like an AR magazine.
 
Last edited:
In the mil spec primers-- the anvil is slightly deeper in the primer cup ( as shown in post #14) -- the combo of the deeper anvil and slightly thicker cup are what help prevent the slam fires-- that said, I've never used the milspec primers and also never had a slam fire-- I've even put a round directly in the chamber and sent the bolt home and never seen a slam fire to date
 
In the mil spec primers-- the anvil is slightly deeper in the primer cup ( as shown in post #14) -- the combo of the deeper anvil and slightly thicker cup are what help prevent the slam fires-- that said, I've never used the milspec primers and also never had a slam fire-- I've even put a round directly in the chamber and sent the bolt home and never seen a slam fire to date
Times 2, exactly with CCI non milspec
 
Warning! This thread is more than 4 years ago old.
It's likely that no further discussion is required, in which case we recommend starting a new thread. If however you feel your response is required you can still do so.

Recent Posts

Top