I understand that the 450 have a thicker cup so in my mind that means that they're more suited to semi-auto with free floating firing pins but I notice the actual diameter is different between the two.

I'm going to be using remmington .223 brass for my first round of reloading .223 so my question is which of these 2 primers is more suited to commerical brass?
Or is that not part of the equation here?

I have used both in my .223 loads.  I haven't had any blown primers with either, but I don't load my rounds really hot either.  I would load 450's unless you just can't find them.

Sarg

Sir, I've also used both 400 & 450 primers.  I do use some fairly hot loads with 77gr SMKs and I like the harder cup of the magnum primer.  I've never noticed any difference in diameter but I don't recall I've actually measured any.  I'll do that later today just for curiosity sake.  I've used the same loads with LC brass that I use with Winchester or BHA brass.  I don't have any indication that there is any difference between the commercial brass compared to LC except LC generally has crimped primers.  7zero1 out.

Thanks for the info fellows.

- Cases that utilize small rifle primers and operate at moderate pressures(40,000 psi) should use CCI 400, Federal 200, Rem 6 1/2, or Win SR. Such cases include 22 CCM, 22 Hornet and the 218 Bee. These primers are also used in heavy handguns such as the 9mm., 357, etc. Other cases that use the small rifle primer can use the above primers only if moderate loads are used. Keep to the lower end of reloading recommendations.

- Cases that utilize Small Rifle primers and operate at higher pressures (.223 Rem, 55,000 psi) should use CCI 450, CCI BR4, Fed 205 and Rem 7 1/2.

- With large rifle primers all being the same thickness, choose a primer that makes the most accurate group, is the shiniest, cheapest or whatever, as they all have similar pressure capabilities.

Hope this clears up some primer confusion.

I would honestly spend the few extra bucks and get some federal gold medal match primers over the CCI small rifle and magnum's.

My CCI's started flattening out significantly at fairly light loads (23.4 grs varget vs 24 grs on the Federal's), and the federals still aren't showing any pressure signs.

My local outfit has only CCI and winchesters.

Was hoping to buy local to avoid shipping and hazmat.

Last summer when it seemed impossible to find primers, especially Remington 7 1/2, I used several hundred CCI 400 with no issues.  However, as someone else mentioned, if you plan on loading up some max loads then I'd use the magnum primers in order to get a good burn.  For plinking they'll work fine.

I prefer Rem 7 1/2's for all .223 loads, they seem more accurate than the CCI #41's in .223 but I get better results with the #41's in 6.8SPC and the 6.8 loads are usually pretty hot and the 41's hold pressure the best out of all of them.

I use CCI 400's for Stick powder loads and the 450's for Ball powder loads. Or Remington 7-1/2's for either if to be used as a match loading.

How do the winchester  WSR primers stack up to CCI's for those who have tried both?

This might help....straight from CCI...http://www.cci-ammunition.com/products/primers/primer_chart.htm

It shows their recommendations.

My .223 loads are new (for me) and light, but for what I have done, the 400s are working fine.

I hope the 400s are ok. My local primer source charges a bit more for the 450 than the 400. and I have 2k of 400s.