I used Remington 6 1/2 small rifle primers in .223 rounds not knowing you shouldn't do that (Thanks to AeroE for telling me).  However, I loaded about 300-400 rounds w/ them already, shot about half and everything was fine.  I'm using 55 grain FMJ bullets and 24 grains of IMR 4895, so I'm about 2 grains below the max.  Will it be OK to shoot what I have left?

Also, why can't you use Rem 6 1/2 in .223 or the other 2 or 3 calibers it lists in print so small an ant would need a microscope?  What could happen?  Seems to me the primer goes off and then it wouldn't matter what happens, as far as the primer is concerned.  However, they must put that on there for a reason, so what is it?

IIRC the 6 1/2 has a thin cup that may burst or be pierced by the firing pin under higher pressures like what .223 rounds generate.

I made the same mistake and shot quite a few before I learned of the error.

I deprimed some and shot the rest.

I would advise depriming, but nothing happened to mine - middle of the road loads though.  YMMV Greatly!

They are just like the CCI-400, they will work on light to mod loads but will pierce on hot loads, some people only use CCI400 primers but they don't shoot hot loads but they are rated for no more than the 6 1/2 is. Like Aero said shoot them but if even one pierce stop and pull down the rest because it isn't worth messing your rifle up for some $.03 primers.

I have never heard that about CCI 400 primers, and I have used quite a lot of them.
 

I've found them to pierce fairly easily, the CCI 400 I mean.  

I'll have to keep an eye on them, thanks.