CCI 400 primers are insufficient thickness for 5.56 pressures.

CCI BR4 or 450 are what you should be using for pressure 55,000 psi+

load up a bunch of 55gr plinker loads

load up a bunch of 55gr plinker loads

You can use them if you want. The BR4 cost more, so you are wasting a penny or so on each shot if you use them for "plinker loads".

It just takes one pierced primer to significantly damage your firing pin and bolt. Two or three, and they are toast.

http://www.cci-ammunition.com/products/primers/primer_chart.htm

400
For most standard loads in cases requiring small rifle primers.

450 Mag†
Magnum primer for ball propellants.

No.41/5.56MM
Military small rifle primer with NATO sensitivity. (resists slam fires)

BR4
Benchrest small rifle primer for critical accuracy needs.

Why would a "plinker load" get a "5.56 pierced primer"?

CCI 400

Use mainly 400's with some 41's and br's never had a issue with the 400's shooting anything from 55-77 grain. Br's are supposed to be more of a precise spark I think and cost a little more

I use 450 for ALL 5.56 ammo

ALL of it.

I doubt you would ever notice a difference in a non match type rifle between "BR" primers and standard primers.

You're just as likely to see as much difference between primers general.

I personally don't load plinking ammo anywhere near 5.56 pressure. In fact I found a sweet spot about 2grs less than most guys use. I have never pierced a CCI-400

Piercing primers isn't always a primer issue either. I've seen certain rifles pierce primers when none other do.

Match primers ars supposed to be made to tighter tolerances. That includes the amount of compound in the cup. So the amount of whatever a fired primer produces the match primers should be more consistent.

So unless you plan on using them in a match rifle I'd say go ahead and use the BR4's.

Just as a side note. I did a side by side load work up using CCI-400 and CCI-450s. From start to maximum you could examine the fired primers under magnification and couldn't tell one from another.

This was from a 20" A3 PSA upper.

Motor

Amen...

I have tested BR4's vs 400s.  Absolutely no difference in my rifles.  Ive tested very hot loads compressed loads with 68-77gr bullets with 8208 XBR with no primer issues with 400s, but in the end, best accuracy came with a lower powder charge so its a moot point.

The only time 450s, BR4s, 41s should need to be used is if you are pushing excessive pressures trying to chase some mil spec pie in the sky number for velocity.  And to be honest, most mil spec loads are garbage for accuracy, so why people try is beyond me.

A lot of published military velocities were fired from 24" test barrels and have no real value when developing loads in shorter tubes. Chronograph your store bought M193 or M855 from "your" barrel and consider that a maximum working velocity knowing you may not safely reach it.

450's BR4's and #41 are all tough primers with the 450's being a great value. It may not become self-evident when loading .223, but these primers do hold more pressure in 6.5x47mm Lapua and 6mm Creedmoor loads than virtually any other small rifle primers.

Remington 7.5's are tough and so are the Russian magnum small rifle primers. The Russian product codes end with an "m" designating their magnum status. kvb-5,56m and kvb-223m.

Don't take my word for it.

I've only been doing this for a quarter century.

Talk to the guys shooting service rifle at Camp Perry. Excluding me I suppose, most of them know a little something about handloading for top accuracy, and they will tell you they are using pretty much any primer other than CCI 400 for National Match ammo. The thicker primers are - by far - the go-to choice for 5.56.

FWIW

In buying all the components from a guy getting out of reloading, there were a few hundred BR4 primers in the package.  With my RARR in 300 Blackout, H110, and Barnes 110gr blacktip hand loads, at 100yd the BR4 primed reloads hit 1" lower and 1 1/2" to the left from the normal impact point when using CCI400 primers (my normal primer used with that load and rifle).  This was unsatisfactory for My Hunting use of that bullet.  I am now using the rest of the BR4's for plinking/closer range practice.  The group size was the same.  Of course, for deer size animals if shooting for the lungs, it probably would have been OK, but not for me.

I'm with borderpatrol on the 450's.  For the very small additional cost, the real or perceived peace of mind they provide is worth it to me.  I use them in everything 5.56/.223/300BO/etc., so it's just one less variable to mess with in the reloading process and one less item to keep stocked.

Some people use cci 400's without any problems, for me I have problems with the 400's with pierced primers, never had a slam fire with one but blown primers was common with higher pressure loads that were no problem with other primers, 205's, 450's, 7 1/2's, CCI BR, for me work like a charm, I won't use them unless I load down a bit, I have several firing pins with holes in the middle of the tip because of 400's and fairly stout loads.

In the 1990's when my rifle team switched from M14's to AR15's, we went through all this drama with primer piercing.

Multiple guns.

Different loads.

All "full-power" loads - that is, not over-SAAMI, but definitely not light loads or plinking loads.

Multiple shooters and multiple guns were piercing non-magnum primers by CCI, Winchester, and Remington.
There was some agonizing over whether changing to magnum primers would have some significant effect on accuracy.
We decided that a chronograph was a good place to start.

Shooting our various loads over the chronograph, and changing nothing about the loads other than switching to a magnum primer, we got no discernible change whatsoever in average velocity.

Decades later, I got a copy of Quickload on my PC.
I find this commentary from the Quickload users manual to be consistent with my experience:

At the time I discoved the problems with CCI 400 primers, I had several hundred cases alread primed with 400's.

I reduced my powder charge by two grains - that's 2.0 grains - not 0.2 grains - and managed to still use those primed cases.

The powder was Vihta Vuouri N540. The reduced-charge ammo seemed to shoot well enough at 100 yards and 200 yards. At least as good as I could hold anyway. And I had no pierced primers with the reduced load.

I still had two bricks of 400's. By then, I had made up my mind to abolish the chaotic practice of having a can-of-this, and a can-of-that, for all sorts of different recipies for all sorts of different calibers. By the time you have over 100 cans, and every can is different from the other can, it just becomes unmanagable. I gave-away those bricks of 400's and never regretted that decision for an instant.

As it pertains to 5.56 I load only three loads now:
75 grain - 24.2 Varget - CCI 450 - 2.250" OAL
77 grain - 24.2 Varget - CCI 450 - 2.250" OAL
80 grain - 24.4 Varget - CCI 450 - 2.400" OAL (exceeds magazine length)

I have data for TAC (for when the Varget factory blows up), but no ammo currently loaded with TAC.

Using only Varget, that easily accounts for a dozen cans in any given competition season.
That's more than enough cans for me to keep up with for one rifle at this point.

And that doesn't even  begin to address the number of cans of spent brass, and brass in various stages of preparation.

So, we'll say the AR is responsible for a good 20 cans.
At some point, decisions have to be made.

When you find the answer to that, and can present your data in such a manner that it can be replicated, you should write a dissertation.

It is very curious that there seems to be no such paper for us to study after all these years.

400s started showing pressure signs prematurely in a lot of my work-ups. Stopped using them years ago in all except low recoil bolt gun loads until they were gone...and never bought them again.

I am guessing you do not shoot highpower and you do not use Varget.

I agree, CCI-400 primers are great for 22 Hornet and 30 Carbine but I would never use them in 223/556 that I load.  Pierced primers and replacing the FP = PITA.

The 400s handle 23.8gr H4895 behind moly'd 77s okay. The indention just starts to move back and a couple newer rifles start to dig into the headstamp anyway.

Perfectly adequate for a moderate charge behind ~50gr bullets for short range use.